1990 to Current

1990 – Audio Research releases the SP-14 preamplifier. This hybrid design is similar to the SP9 Mk.II with one 6DJ8 dual-triode vacuum tube in the second gain stage of the phono section. The line section is all-FET, using a circuit similar to that in the SP15, the then-current top-of-the-line model. The SP-15 includes absolute phase, phono high-pass filter, and front-panel impedance selection for cartridges, which the SP-14 omits.

1990 - Michael Elliott and his company Counterpoint release their SA-5000 hybrid preamplifier which was sold until 1993. Counterpoint declared bankruptcy in 1997 (Stereophile writeup from July 1998: https://www.stereophile.com/news/10202/), and Mike’s follow-on company, Alta-Vista Audio which serviced, supported and upgraded many of the Counterpoint products is also long gone since his retirement and departure from the industry in 2012.

While it showed incredible innovation and thinking, it—like many of their other products—reportedly exhibited poor reliability. The SA-5000 is a complicated design with a myriad of low-wattage, low-voltage elements, being floated 360V and/or 240V above ground, on a rubberized-physically-floating chassis as well (in which at least the first production run reportedly featured too-short of physical cabling across the gap). It is fairly unique in the use of BUF-03 video buffers on a +/-24VDC power supply riding in the midst of high-voltage vacuum-tube circuitry with a rather ingenious floating bias supply for manual DC-offset correction.

Properly shipping an SA-5000 back to the factory for needed repairs appears to have required the user to scrupulously follow the directions regarding which length screw went where (in order to secure the mechanically-floating subchassis for transit). Deviating from these directions could enhance any existing damage.

Speculation has rested on dealers turning their backs on Counterpoint over the mid-1990s based on reliability concerns, as well as the cratering of the Far East audio market after the October 1997 Asian currency crisis, as being either principal, or contributory, drivers to Counterpoint’s ultimate failure. We can only imagine what a disappointing endeavor it must have been to have participated in, no matter the proximate cause(s).

The SA-5000 service manual appears to have notes showing that it was laid out in early 1989 directly into a production PCB from a near-clean sheet of paper. Minor tweaks were laid in based on the prototype, and it would appear to have been released to the market. It is pure speculation to assume this was related in any way to “infant mortality” failures. However, in general, we try to be aware of straying too close to designs that could be considered “too clever”. Just because you “can” do something does not mean that you “should” do something. Tradeoffs are part and parcel of the experienced designer’s repertoire and second-guessing is inevitable. To balance this out, we do hear occasionally from clients who have the follow-on SA 5.1 model and state that it has been running for years with no issues, but do comment on its tremendous power consumption. Consensus from this handful of clients converges on our MP-7 outperforming the SA-5000 and SA 5.1 in their MM modes, at much lower power consumption, heat generation and space.

We don’t know to what extent, if any, the SA-5000 and similar products from this manufacturer relied upon computerized modeling in the design phase. However, the line between complexity and reliability is one reason that we tend not to reply upon electronic SPICE modeling for our designs. We prefer intuition, Ohm’s law, breadboarding, real-world objective measurement, and testing, followed by iterative live auditioning.

While this is unrelated particularly to Counterpoint, the analysis and discussion of the SA-5000 reminds us that on surprisingly-too-frequent of occasions, a designer will think they’ve invented something absolutely, positively amazing, and have never seen anything like it before. Then they are chagrined to uncover some very-obscure minor reference to it in a circa-1959 schematic that clearly shows the same concept being applied, but, to the best of the designer’s knowledge, they’d had absolutely no previous exposure to it. We have been able to find other examples (going back decades) of this happening elsewhere, sometimes not seen or discussed until decades after "finding the prior art”, which is, depending on your perspective, rather modest comfort.

1991 - Digidesign offers Pro Tools, a 4-channel, 16 bit non-linear audio editor for $6000.

1991 - Orban introduces the Optimod 8200, their first digital FM broadcast audio processor. The Orban 8200 offers a mode emulating the 8100 two-band processor with phase rotation, or a Purist 8100 mode. It also offers a 5-band processing structure which will become standard in American broadcasting via future Orban models 8400, 8600, and 8700.

Utilizing 32kHz internal sampling on Motorola 56001 DSPs, the 8200 kicks off the processor war of the early to mid-1990s between Orban and their principal competitor Omnia who offer the Unity 2000 processor, which despite digital control, is actually an analog processor internally. Aphex Systems offers their 4-chassis Aphex Audiophile Air Chain combining the 320 Compellor, 700 Dominator, a stereo LF/HF Exciter and Stereo Generator. These will be later combined into the Aphex Model 2200 FM broadcast processor, a 2-RU high dedicated unit. It’s “Photocell-based HF limiter” will later be replaced with a faster-responding unit as an optional update.

Digitally-compressed STL (studio to transmitter links) will be introduced by Moseley, using APT-X Lossy encoding. A 1991 Stereophile article mentions this, although not by name, in an interview with Richard Cabot, Vice President of Oregon-based audio analysis test equipment maker Audio Precision. https://www.stereophile.com/interviews/850/index.html. Stereophile Technical Editor Robert Harley and Dr. Cabot talk about the Phillips TDA1541/SAA7220 Digital Filter combo, and how one of his clients is using the Philips chipset in a broadcast application and had figured out how to correct the typical 6dB or greater of low-level non-linearity by simply re-squaring-up the digital pulse waveforms going-into and coming-out-of the chips. Some stations will deploy these and keep them on-air for a few months, later pulling them off and returning to a traditional analog composite STL for more natural sound quality.

1991 - Hovland introduces the MusiCap, a polypropylene-and-aluminum-foil high-end capacitor which will go on to be utilized by more than 200 audio companies.

1992 - Vacuum Tube Valley (VTV) magazine is introduced which publishes through the year 2000.

1992 - Sound Practices magazine is introduced by Joe Roberts which will publish 16 issues and articles for an incomplete 17th issue slated for 2000.  Back issues are available in PDF format on CD via eBay.

1992 – J. C. Morrison publishes his DIY Siren Song RIAA phono preamp.

1992 - The Russian 6H30 tube is introduced by Balanced Audio Technologies

Soviet tube technology is becoming available in the secondary marketplace, which will be further enhanced by the development of on-line auction sites in a few years as availability and interest in the Internet spread worldwide.

1992 - Burr Brown releases the OPA604 series of op amps, including the dual OPA 2604. They will run on rails up to +/-24VDC. The datasheet contains multiple references to sound quality of J-FETs and a box labeled “distortion cancellation” which was patented. Sound quality impressions appear to be sharply divided into supporters and detractors, as with many other of the 1990’s Burr Brown op-amps.

1992 - The POOGE-4 series of articles is published in TAA The authors significantly improve the performance of the Phillips DAC-960 DAC converter, which is a standard Philips 4X Oversampling design executed with the selected Crown TDA-1541-S1 DAC chip and SAA7220 digital filter. 

1993 – Analog Devices develops their XFCB (Complementary Bipolar) 24V process which will create op-amps such as the AD8610.

1993 – Melos SHA-1 Headphone Amp and Line Amp employs 1 x 6DJ8 with an IRF-730 single-ended output stage. It gains traction at Stereophile where JA uses it as part of his reference system for a year or two. Years later, independent analysis (available online) reveals quite substantial technical flaws in the basic circuitry. Unstable power supply regulation with high noise and ripple, when corrected, elevate the performance. Like Counterpoint (above) Melos’ reported questionable-reliability and repeated failures may have contributed to the downfall of the company by the late-1990s. We have observed hand-drawn schematics and layouts of the SHA-1 series that appear to be factory-created; very ’back-of-the-envelope’ in style. It is unknown to us whether-or-not these were leaked or redrawn by a consumer, but their supposed official nature does give us pause, when CAD design was well established by the mid to late 1980s.

1993 – Rotel’s High End Series is introduced. The RHQ-10 Fully Discrete phono equalizer will be sold through 1997. It features an emitter-follower power supply, double regulated, but as no power supply feedback is used, the regulator output is of moderate impedance.  The signal path consists of two cross-coupled stages with combined passive/active EQ.

1994 – On the new, larger January Cover of Stereophile – “If One Is Right, the Other Must Be Wrong” – the Single Ended Triode phenomenon from Asia is examined. It is a harbinger of the commercial arrival of newly produced SETs - the phenomenon is no longer limited to old Western Electric theater amplifiers from the 1930s and 1940s and the Do-It-Yourself hobby.

Stereophile moves back from the small-format magazines to the larger 8 ½ x 11” format, returning to its old roots and old size which were introduced in 1962 by J. Gordon Holt and ran until the original downsizing to digest-format in 1968.

1994 – The Zen Amplifier is published by Nelson Pass in TAA 2/94.  Together with the matching Bride of Zen preamp in the next issue (3/94) show the continued interest in, and fine audible performance of, simple and unique solid-state (in this case, MOSFET) circuitry. They are offered for “non-commercial use only”.

1994 - Rotel introduces a stand-alone mid-price phono preamp, the RQ-970BX Phono Stage.  It is a hybrid discrete and IC op-amp based design, using an input low-noise differential BJT pair feeding an Analog Devices AD744 to an NE5534 per channel with multi-stage equalization.  It has an unusually long life in their product line, remaining in production through 2012.

1994 - Digidesign is acquired by Avid Technolgies of Burlington, MA. The Digidesign brand (Pro Tools being their flagship product) will eventually be phased out by 2010 in favor of branding as Avid.

1994 - Leonard Feldman passes away, and an industry-focused memorial is published in the JAES by then-still-editor of AUDIO magazine, Gene Pitts. The same year Ralph Hodges also passed away; Ralph had a long-time column in Popular Electronics called “The High End”. JGH also had a column in Popular Electronics in the early 1970s.

1995 - The original Lehmann Black Cube Phono Preamp is introduced, using a SSM2017 input op-amp and 1 x OPA2604 output op-amp, with passive RIAA in between.  It will be replaced in 2006 with a new unit at a similar price point, using 2 x THAT1510P input amplifiers and 2 x OPA134 output op-amps. A notably-similar DIY design will be published in an Italian website in 2002.

1995 – Gene Pitts forms The Audiophile Voice after editing AUDIO magazine for more than twenty years.  AUDIO will go through additional editors, ending with Corey Greenberg (formerly a reviewer for Stereophile in the early 1990s) and will end publication in February 2000 after continuous publication since 1947 (in a previous incarnation).

1995 – A famous Single-Ended Tube amplifier manufacturer located in North Carolina copies the Zen amp and Bride of Zen preamp from last year’s TAA articles and sells them as commercial products.  The manufacturer’s name, as well as town, bear striking resemblance to an upbeat song on Joni' Mitchell’s 1971 Blue LP. This action is called out by Nelson Pass and the models are promptly discontinued.

1995 - Creek introduces the OBH-8 and OBH-9 phono preamplifiers. Music Hall requested the design of a small add-on RIAA stages (from Musical Fidelity) to support turntables, as built-in phono stages were declining, and separate mid-level phono stages were rare.

1995 - Rolls/Bellari of Salt Lake City, Utah introduces the dual microphone preamp model RP-220. It is based on the Dynaco PAS preamp circuit with a small microphone input transformer. It includes a +250V B rail to a unity-gain balanced op-amp output buffer based on a single Rohm BA-4560 op amp per channel, running on one single 12V power supply rail, which also supplied the tube filament directly from a noisy 7812 regulator. The same basic circuit is used in the smaller MP-105 and MP-110 single channel preamps.

They also introduce hybrid Moving Magnet Phono Preamps, beginning with the VP-529, later VP-530 and current VP-530 MkII. The VP-529s that we have examined have a rather non-flat frequency response, up 3 to 4dB in the bass and down 2 to 3dB in the treble (the specs were tighter). Switching in the optional VP-529 rumble filter (18dB/octave) caused a peak in bass response at 50Hz. The VP-529 schematic shows a textbook 1:3 RIAA network, but it is fed by a complex impedance from the tube plate which was not taken into account. Such iteration and trimming in the design stage would be necessary to achieve a relatively flat RIAA response.

1995 - Conrad Johnson Reference Series is introduced, using the unusual approach of zero feedback with 10 paralleled 6H30s to deliver a low output impedance from a conventional amplifier stage, while not using an output cathode follower.

1995 - The Woodside SC26 preamplifier is positively reviewed by Larry Greenhill in Stereophile. Woodside was a continuation of the British manufacturer Radford, whose principal Arthur Radford retired in 1986. Former staff formed the Woodside entity, but the STA-25 Mk III amplifier received a poor review from Dick Olsher in Vol. 10, No. 6 (1987). They went back to the drawing board with assistance from American Arnold Weisenberg who helped design the SC26. It used nine 12AX7s and one 12AT7, each tube being operating on a separate (solid-state-regulated) power supply. The RIAA gain stage was feedback-based with a return-to-zero capacitor between V1 and V2.

Double-regulation was employed, each of these secondary regulators being sourced from a primary 310V supply. Filaments were separately regulated. The SC-26 used SEPP-connected 12AX7s in gain blocks which were followed by 12AT7 cathode followers. Low noise Moving Coil operation was via Sowter input step-up transformers into the first 12AX7 phono gain stage.

The SC-26 was intended as a companion to the Woodwide MA-50 amplifier, which itself was a substantially reworked and modernized STA-25. The MA-50 was positively received by LG in a 1994 Stereophile.

1996 - Professional Audio Company dbx introduces hybrid mic preamps. Some reviewers find them to be rather bright and transistory-sounding.

1996 – Robert Harley leaves Stereophile and becomes editor of The Absolute Sound

1997 - TLE2072, the second generation of the TL072 series of op-amps. Texas Instruments ‘Excaliber’ series is based on a modern architecture that produces PNP transistors of high gain and high transition frequency.

1997 - Burr Brown releases the OPA134 series, to be used widely in Proceed and Mark Levinson gear as well as others. Some characterize it’s sound as “smooth” and “laid-back”.

1997 – Late October brings the height of the Asian Financial Crisis. Sonic Frontiers subsequently declares bankruptcy and is purchased by Paradigm Electronics (related to the speaker company) in Canada. 250 people and 4 plants are affected. The DIY branch reforms with a slightly different name.

1997 – Lynn Olsen provides excellent analysis of feedback-free and Single-Ended-Triode amps.

1998 - Ron Sutherland’s Acoustech PH-1 phono preamp, built at the request of Chad Kassam of Acoustic Sounds, was reviewed by Wes Phillips in the June 1998 Stereophile. Ron will eventually go on to found Sutherland Engineering to produce a broad line of similar phono preamplifiers.

1999 - Brian Damkroger of Stereophile comments on the state of the mid-price phono preamp market. He states that, in his view, the Audio Research PH3 ($1495), the Linn Linto ($1500), and the Acoustech PH-1 ($1200) are all ‘great choices’ in the $1000–$2000 price range.

1999 - Sonic Frontiers Phono One ($1999) hybrid design uses a single JFET per channel as an input, followed by a 6922-based triple-series amplifier as a second stage. The output stage uses another 6922 as a cathode follower to lower the unit's output impedance. The circuit is noninverting and uses frequency-dependent feedback for equalization, with a single compensation network being "fed from a fairly low impedance, thereby avoiding slew-limiting at high frequencies." 54dB of gain is standard, but 44dB and 62dB are also available as special orders from the factory. Stereophile provides a lukewarm reception.

2000 – In February, AUDIO magazine ceases publication after 51 years.

2000 - Hovland introduces the HP-100, a one-box, all-tube line stage ($4995) with optional built-in MM ($5995) or MC ($6495) phono stage.

2000 – Spectral releases their DMC-30 Reference Preamplifier. Upgraded modules are released through next few years, and the basic platform remained current two decades later.

2000 - Jim Fosgate of Fosgate Research (specializing in surround sound processors) publishes two of his reference preamp designs, one very similar to the Harmon Kardon Citation IV, and one of his own designs, in what would have been Sound Practices Issue 17 when it ceases physically publishing. (Issue 17 material is included in PDF reprints). Both use feedback around tube stages with the Citation IV using passive RIAA in the middle, or in two stages with active feedback.

His introductory quote is worth reading:

“Like most people, I went “Solid State” when it came along. I remember wondering why my collection of records didn’t sound as good as I thought they once did. I thought it was because my listening abilities had improved or my taste in music had somehow changed.

In the late Seventies, I invited a friend over to audition my system, a setup that I was quite proud of. This guy was a classical musician and tube listener. After listening for a while, his only comment was: “If you have a chance, you should listen to some tube equipment again.” This stuck in my mind and one day at a garage sale, I found a Dyna Stereo 70, PAS Preamp, and FM-3 Tuner for nine bucks, similar to the ones I had once owned. The amp needed a 5AR4, and a fuse, but the tuner and preamp were working, so I decided to give them a listen.

I was really surprised! This old stuff was blowing my solid state stuff away! My mind was boggled. My old records even sounded the way I remembered them. There was only one thing to do: sell all my solid state equipment, go back to tubes, and never look back again.”

2001 - Daniel Cheever publishes his Master’s Thesis which is a fascinating and in-depth analysis of solid state vs. tube audio amplifier technology, focusing especially on the relative proportion of high-order harmonic distortion and how it compares to the human ear’s own distortion and audibility profile. It examines in detail a Hafler DH-500 MOSFET amplifier, rated at over 200W/ch, with a single-ended Type 45 tube amp with only a few watts and concludes that the tube amplifier has a sonic signature that is more closely aligned with the ear’s masking profile.

2002 - A passive EQ FET preamp design with BF245s and 24VDC supply is published on a hobbyist Spanish internet site. It has low headroom and significant design constraints including high measured distortion but does not require any component matching.

2002 - An inverting FET/BJT Line Amp design is published on TNT Audio. It uses a 40V rail.

2003 - Joseph Norwood Still Passive EQ RIAA FET preamp is published in Audio eXpress’s April 2003 issue. It is later modified in private correspondence (2006).

2005 – Price inflation in high-end audio appears to take hold. 

See comments at: https://cdn.stereophile.com/content/superphon-revelation-preamplifier (April 2019)

2006 - A new Version of the Lehmann Little Black Cube is introduced, at a similar price point. This version uses 2 x THAT1510P input amplifiers and 2 x OPA134 output op-amps. The original input amplifiers (SSM2017s) were discontinued by the manufacturer, and the expensive OPA2604 will eventually be discontinued as well. The new model adds additional custom cartridge loading options.

2008 – Audio Research is sold to a private equity firm.

2009 – Jim Thiel passes away; Thiel Loudspeakers is sold in 2012 by Kathy Gornick to a group of non-audio investors, goes through a series of CEOs and designers, moves from KY to OH in 2014, and is bankrupt in March 2018.  Longtime employee and engineer Rob Gillum https://www.coherentsourceservice.com/ provides quality service to the Jim-Thiel-era models.

2009 - Hovland Corporation closes its doors in early 2009. Originally known for custom tonearm, interconnect, and speaker cables, dating back to 1979 , and then introducing the Hovland MusiCap capacitor in 1991, they had more recently introduced a small line of striking-looking electronics, beginning with the HP-100 tube preamp in 2000. One of their employees was Robert Morin, who will later go on to found Lounge Audio in 2011.

2009 – In February, The Absolute Sound Interviews Spectral's Richard Fryer and Keith Johnson.

2010 – Jan Didden starts Linear Audio magazine which continues through 2015.

2010 – SimAudio MOON 110LP introduced and sold through 2018.  It is an op-Amp based design augmented with 4 discrete transistors, and utilized an 18V external DC supply.  It is replaced in 2018 by the 110LPv2 which uses a 24V external DC supply.

2011 - Edward T. Dell sells Audio Xpress to Elektor Publishing and reluctantly agrees to retire.

2011 - Lounge Audio introduces the LCR phono preamp for $200. Housed in a striking wooden box with brass nameplates front and rear, and gold hardware, it is positively reviewed by Tone Audio.

2011 - Ron Sutherland’s Sutherland 2020 Phono Preamplifier is reviewed in Stereophile. It features two +48V switching wall warts and substantial passive R/C filtering. The gain circuitry relies on conventional op amps which are preceded by a mic preamp chip.

It uses a Texas Instruments INA163, followed by a Burr-Brown OPA134 FET-input op-amp, and a Burr-Brown OPA627 op-amp as a DC servo. This is conceptually similar to the Lehmann designs.

Frequency response rises sharply above 20kHz in an attempt to conform to what hobbyists call the Neumann “5th RIAA Time Constant” at 50K. Allen Wright, since deceased, claimed in 1995 that it was present in Neumann cutting lathes and “was designed to prevent the cutterhead from burning itself out”.

Neumann cutting lathes feature a second-order Bessel high frequency filter set far above 50kHz which primarily tackles Radio Frequency Interference (which in Europe’s Long Wave service begins at 150kHz). The filter is designed to have minimal impact to the RIAA curve. In any case, a second-order filter could not be accurately replicated by a single order “F5" pole”, even if it is placed low in frequency close to the audio band.

A design of this type may be prone to high frequency transient overload and slew-rate limiting from LP ticks and pops. It also provides significant phase lead from 5kHz to 50kHz which some listeners may find sounds pleasantly “zippy” on certain program material, but others may perceive as over bright.

2011 – Coincident Statement Phono Preamp. A high gain, all tube unit employing MC step up transformers. 2 tube gain stages are used per channel. RIAA curve is implemented passively with zero feedback. The price is US $6499.

2012 – ‘Sam Tellig’ discontinues writing for Stereophile in late 2012 after becoming irate over late payments made to writers. Editor John Atkinson attributed these issues to the change in accounting system at the new corporate parent. John remained typically gracious in on-line exchanges with ‘Sam’ as they parted ways.

Many former Stereophile reviewers are still active and sought after in other publications, including Robert Harley, longtime editor of The Absolute Sound (since the mid 1990s); Dick Olsher of EnjoyTheMusic.com, George Graves and Anthony Cordesman with The Audiophile Voice (published by former longtime AUDIO editor Eugene Pitts), and others. JGH passed away in 2009 after parting ways with Stereophile in 1997. Larry Greenhill appears to be one of the longest term Stereophile reviewers, with more than 30 years of reviews in print. HIs audio reviews were first published nearly forty years ago in Ed Dell’s Audio Amateur (which later became Audio eXpress).

2012 – U-Turn Pluto Preamp is released to support the new U-Turn Audio turntables, produced in Lexington, MA. It is a single NE5532 design, operating on a single regulated voltage rail of 11V, and appears based on a 1983 design note. At least 7500 units appear to have been shipped.

2013 - Edward T. Dell, longtime publisher of The Audio Amateur, Audio eXpress, Glass Audio, Voice Coil, and Speaker Builder, passed away at the age of 90 in Peterborough, NH. He sold the aX magazine empire in 2011. ETD first published a DIY article in JGH’s Stereophile in 1966, a substantial rebuild of a Dynaco amplifier. Stereophile reader feedback was vicious and DIY wasn’t well accepted by the readers. ETD would start TAA in 1970 which became one of the premier magazines for advancing the state of the audio art, especially from the mid 1970s through the mid 1990s. It has now (as of this writing) been refocused on Pro Audio and Consumer Audio Integration and is doing well. Darlington Labs owns a nearly complete set of TAA from 1970 to current date, as well as Stereophile 1966 to present as part of our extensive reference library.

2013 - Shannon Parks of Parks Audio in Washington state releases his tube-type MM-style phono preamp, the Budgie. It is a 6DJ8-based design running on 75VDC power rails sourced from an internal switching power supply. Active feedback EQ was utilized around both tubes. Metalized film capacitors bypass the power supply rails and couple the signal between stages and to the output. Due to the lack of output buffering or an output cathode follower, output impedance was specified at 6 kilohms.

We measured ripple at 2.4mV AC on the main power supply rails in a 2015-production sample, similar to the range of a typical cartridge input signal. It is a testament to the active current loading at the tube plates, employed via TO-92 transistors which are biased with large red LEDs, that some of this noise is rejected. The tubes receive operating bias from an unbypassed small-signal silicon diode in the cathode circuit. Note that this fixed bias arrangement results in unusual sensitivity to tube changes or “rolling”, with the bias point varying between 32V and 46V on a random sample of 6DJ8s we had close at hand. Measured gain is 38dB at 1kHz with quite accurate RIAA equalization. External power is provided by a 12VDC switching power supply.

Midway through the production run, in an attempt to reduce interference from RFI (due likely to the unshielded and RFI-prone frame-grid high frequency vacuum tubes operating completely outside of the die-cast aluminum chassis) a 15pF ceramic capacitor was placed from the grid to the plate of each input stage of the 6DJ8. This resulted in a marked increase in effective input capacitance to more than 400pF. Audible upper-midrange-peaking and subsequent dulling of the frequency response with most traditional highly-inductive moving-magnet phono cartridges would be the expected result, and was reported by users, some of whom enjoyed this type of sound.

Note that such frequency response disturbance would not be found in most bench testing because the signal generator presents a low impedance to the tube grid. This is unlike the phono cartridge - some of which are 40 kilohms or more in the top octave due to resonant-tank-circuit effects.

This model was discontinued by the manufacturer in May 2018, who moved exclusively over to an NJM2114 op-amp-based input stage, opeating flat - with no EQ - directly into an active A/D, DSP, and active D/A output, using the same Hammond die-cast enclosure. Readers can find an analysis of the headroom challenges of this topology (“RIAA entirely via DSP EQ”) and other measured performance of the unit in a review on the ASR (Audio Science Review) website.

2015 – Dick Olsher reviews the Jadis entry level phono stage in The Absolute Sound.  http://www.theabsolutesound.com/articles/jadis-dpmc-phono-preamplifier/ $6900. It has a tube regulated B+ rail using a tube-based series pass regulator consisting of an EL84 beam power tube and an EF86 pentode, and 4 x 12AX7 tubes in a feedback configuration. He concludes that “as the DPMC amply demonstrates, there is plenty of magic left in the classical approach, especially when coupled with a modern, well-regulated power supply.”

2015 – Doug Sax of The Mastering Lab passes away. Chad Kassem is reported to have purchased most of the gear (primarily tube-type, designed by Doug’s brother Sherwood) and moved it to his Kansas headquarters of Acoustic Sounds.

2015 - Blaupunkt GmbH, the car audio manufacturer, files for liquidation and bankrupcy. Owned by Robert Bosch GmnH from from 1933 until March 2009, it was sold to Aurelius AG.

2016 – McIntosh introduces two new stand-alone modern phono preamplifiers, for the first time ever (since their short-lived moving coil step-up sold from 1983 to 1987)

The MP-100 sells for $2,000. The MP-1100 sells for $8,000 with 2 x 12AX7 per channel for total of 4 x 12AX7.

2016 - Schiit Audio releases their Mani phono preamp. The unit undergoes 3 revisions, internally denoted as 1.0, 1.1., and 1.2, one of them appearing to attempt to fix a larger-than-expected susceptibility to RFI (radio frequency interference) and another addressing an “end of life” issue for one of the critical op-amps.

2017 – Mark Levinson’s No. 526 is reviewed by Larry Greenhill of Stereophile. The current Mark Levinson line uses a combination of Folded Cascode circuit topology—built with junction field-effect transistors (JFETs) and bipolar junction transistors (BJTs)—with a fully balanced, dual-mono, and ultimately direct-coupled signal path, which is “intended to achieve high gain, low noise, wide bandwidth, and excellent linearity”. This model is compatible with moving magnet and moving coil cartridges.

2017 – PS Audio BHK Signature in the May Issue of Stereophile.  https://www.stereophile.com/content/ps-audio-bhk-signature-preamplifier.  The PS Audio ($5999) is 37% cheaper than the Pass—but I've found that the BHK Signature performs above its price class. That made for a good comparison.

Compared to Pass XP-22 $8600 and the PS audio outperformed it.  Pass also offers a $38,000 preamp.  Unknown result to compare that model against BHK.

Read more at https://www.stereophile.com/content/pass-laboratories-xp-22-line-preamplifier-page-2#04xhCTzsxzLSFq8j.99

The BHK Signature preamplifier ($5999 in black or silver) marks a surprising turn for PS Audio: It has tubes. That's surprising because CEO Paul McGowan has long been anti-tube. "It's not that I do not like the sound of tubes, I always have," he recently wrote on the company's website. "I just never felt their frailties were worth their sonic virtues, and I was convinced we could do as well without them."

He recently changed his mind, thanks to amplifier guru Bascom H. King—the BHK in the name of the company's BHK Signature line—who was recently lured from semi-retirement to create two new power amplifiers and this preamp.

Why the change of heart? The story, as told in videos on the PS Audio website, is that McGowan asked King to design a preamp, and King accepted, on one condition: tubes. There's just something magical about a tube, King says—something intangible. McGowan listened, agreed, signed off, and the BHK Signature preamp was born.

Read more at https://www.stereophile.com/content/ps-audio-bhk-signature-preamplifier#gw5Fx1xwFTMAp16y.99

Bascom King was a long-time reviewer and columnist for AUDIO magazine in addition to his other pursuits.

2018 – In March, Thiel Loudspeakers declares bankruptcy. According to reporting by https://www.strata-gee.com/ $10 to $12 million had been sunk into the company, and it had suffered through 5 separate CEOs since the new owners purchased it in 2012 (after Jim’s death in 2009). Kathy Gornick, Jim’s longtime business partner, had exited rapidly after getting to know said new owners. The Kentucky factory was sold along with much of the tooling and parts in 2014 and most staff was let go. Existing stock was sold down through 2016.

We had the misfortune of encountering a chief marketing representative of the “new” Thiel April 2017 in their AXPONA exhibit room. We overheard him actively belittling the entire Jim Thiel philosophy of phase linearity and the “Coherent Source” topology to a potential client. More than one other audience member was visibly uncomfortable. Meanwhile, egregiously overpriced, blandly-finished, textbook “designed-in-Canada with high-crossover-slope” speakers were on static display. Thiel was curiously absent at AXPONA April 2018, and we discovered that they had declared bankruptcy the month before.

A major magazine had auditioned the smallest pair of the new line and tried very hard to give it a good review, based on 35 years of goodwill towards Jim and his staff. Memories of Julian Hirsch (longtime reviewer for Stereo Review) flashed in our mind: “of all the speakers I have reviewed, this is certainly one of them.”

The “new Thiel line” was refusing to hit their reserve price of less than 10% of retail on eBay a few months later. Perhaps thankfully, its chief designer had already left the now-failing company.

Longtime Thiel employee and engineer Rob Gillum https://www.coherentsourceservice.com/ services the Jim Thiel era units (we can personally recommend him) and classic-era Thiel’s not only remain the cornerstone of some extraordinarily fine systems, they are true “sleepers” in the used market. Models to particularly look out for include the CS 2.2 and CS 3.6, both of which have amazingly linear impedance curves and mate well with vacuum tube amplifiers. Those models contain tweeters which are custom versions of Vifa metal domes with an extra low primary resonance, and a 4 ohms coil winding. They have, unfortunately, proven to be prone to delamination after many decades. Rob can rebuild the driver with new butterfly assemblies, and this would appear to be a solid investment.

2018 – John Atkinson retires from editing Stereophile at age 71, and Jim Austin assumes the duties, younger by about 15 years.

2018 – David Wilson of Wilson Audio passes away; his son continues the business.

2018 – Conrad Johnson is sold by Lew Conrad and Bill Johnson to the head of their marketing department.

2018 - In May, Parks Audio releases their Puffin, a DSP-based phono preamp utilizing NJM2122 op-amp preamp stages with flat gain structure, and all EQ in DSP courtesy of a TI PCM1808 A/D and TI PCM5102A D/A stage. It features a 20mV input overload at 1 kHz (40dB gain setting as measured by Audio Science Review) which is exceeded by many Moving Magnet cartridges playing heavily modulated records, or during transients caused by ticks and pops. By comparison, the overload of Darlington Labs products at 40dB gain is typically 140mV, or 17dB higher than the Puffin.

DSP functions such as those built into this unit may lessen the audibility of gross-input-overload on surface noise, although probably not wholesale clipping on program material. Decreasing the input gain (instead) will further compromise the signal-to-noise ratio of the input A/D and output D/A converter as well as produce lower-than-desired overall listening levels in many systems. This nearly-insurmountable bottleneck is perhaps why this “all-EQ-in-DSP” approach, as advocated by a few commentators, is relatively rare in the marketplace.

Certain reviewers and some owners have found this Parks unit to be a fun device with many flexible EQ settings and a treasure trove of adjustability, particularly for collectors of very old pre-RIAA LPs or records which are heavily damaged or otherwise deploy this unit as “second” to a primary phono preamp, or at line level for its DSP. Reviews in advertising-supported publications seem to emphasize the “fun” aspect.

It has been reported that Puffins with serial numbers 1020 to 1122 have ESD diodes on the input for extra protection. These are not 1N914 or 1N4148 diodes as typically seen when protection is needed, as they lead to an input capacitance of 300 pF instead of the specified 50 pF (which denotes a power rectifier type). This could certainly explain some of the variable reactions to the unit. Interesting to note that late Parks Budgies (the tube unit) had approximately 400pF input capacitance due to an RFI capacitor that was added long after production had started.

2019 – Jack Renner, co-founder of Cleveland-based Telarc Records, passed away at the age of 84 in June. His label pioneered the wide commercial use of the 50.4kHz, 16-bit Soundstream digital recorder in 1978. He was known for his widely-spaced orchestral recordings using primarily Schoeps omnidirectional mics to produce a big and powerful (and detractors might say vaguely imaged) sound quality.

2020 - In October, Darlington Labs opens to the public and introduces the all-discrete high-voltage J-FET MM-6, MM-5 and MM-3 phono preamplifiers, using their unique intellectual property which was more than four years in active development.

2020 - Six Acoustics, a new Canadian audio manufacturer based in Toronto, Ontario, Canada, debuts their York Acoustics phono preamplifier for ~USD $400. US-based manufacturer Hagerman Technologies alleges that the York Acoustics unit directly copies the Hagerman Bugle (op-amp-based) phono preamplifier, with extremely minor changes, which is available from HagTech for about half the price in a different enclosure.

Jim Hagerman, in a Stereophile forum, stated that the Canadian unit is a “near clone” with “goop on top of the PCB” to disguise the origins. The York phono preamp appears to have started life as a failed Kickstarter campaign.

Six Acoustics claims +/-0.01dB RIAA tolerance but the “original designer” says that this is impossible in normal production, +/-0.1dB being optimistic using 1% tolerance resistors, and +/-0.4dB being typical using 5% tolerance components. Six Acoustics website advertises that “What we value here is honesty and integrity in engineering and performance“.

2021 - McIntosh introduces a newly-reimagined version of their MI-3500 350 watt/channel tube amplifier which originally sold between 1969 through 1971, and was featured as part of the Woodstock August 1969 PA system as well as the 1973/4 Grateful Dead “Wall of Sound”.

2021 - In May, Darlington Labs introduces the MP-7 phono preamplifier.

2022 - Schiit Audio released a new version of their Mani phono preamp in late February. Pricing increased from $129 to $149, and the WIMA polyester capacitors have made way for surface-mount units. It is referred to as the Mani 2 on the underside, although the prior version went through three “internal” revisions (noted as 1.0, 1.1 and 1.2) in attempts to deal with RF susceptibility and end-of-life for one of the originally-specified (12V-max-supply) op-amps.

Gain ranges have been increased by approximately 5dB. It is also reportedly significantly quieter. The power supply rails have been raised from +/-5V to +/-16V, which will improve input overload specifications, a particular limitation of the earlier unit. This completely revised design remains all-op-amp-based, as expected at this price point (for non-Darlington Labs units) and uses a single set of bipolar IC voltage regulators.

2022 - In March, Darlington Labs introduces their line of Moving-Coil Active Step-Ups, beginning with the SU-7, and quickly followed by the SU-6 and SU-5. In April, Darlington attends its first trade show as a corporate entity at AXPONA in Schaumburg, IL (a suburb west of Chicago), exhibiting at a booth in the Expo Hall. Staff attended the 2017 (old location near the airport) and 2018 (current location), skipping 2019 in favor of planning for the company rollout; the trade show was postponed multiple times and canceled during calendar year 2020 and 2021 due to local and global restrictions on travel.

2022 - In December, Parasound owner and founder Richard Schram sells the company to David Sheriff who has a 30-year career in running manufacturing and distribution companies as well as being a systems consultant, but who appears to be new to the mid and high-end audio space. Designer Darren Meyers leaves PS Audio and goes to work for Parasound, potentially assisting John Curl with primary design responsibilities.

2022 - In December, James M. Fosgate passes away at the age of 85. Jim Fosgate invented the aftermarket car stereo power amplifier in 1973 with Rockford-Fosgate, and after his departure from R/F in 1981, remained active in audio, and particularly in surround-sound decoding technology, leading the team that developed Dolby Pro-Logic II.

2023 - MQA declares bankrupcy in April - https://www.creditman.co.uk/company-notices/company/09123512

https://www.whathifi.com/features/mqa-has-gone-into-administration-what-does-this-mean-for-tidal-and-supported-products

Interestingly, a former design consultant for Darlington Labs was insistent in 2016 that we must absolutely, positively get on the MQA bandwagon. We looked at licensing costs and acquired proprietary information to be considered as a manufacturer. In the end, we parted ways with this consultant in early 2020 as we launched the company. We consider the bankruptcy of the MQA IP shell a welcome sight, as we found that it was not at all transparent to the high resolution source.

Our former consultant’s ideas of what was necessary in the marketplace ended up being diametrically opposed to what the majority of our other interested partners believed. In the end, for us, the marketplace has spoken.

We note, with some amusement, that the proprietor of the ASR website, who owns a turntable that was given to him (which he has never installed) yet loves open-reel tape on an Otari 5050-B-II, was a huge proponent of the MQA technology in 2017, declaring it “the only proper thing going”. This ASR owner, in his prior capacity as a senior Microsoft director, enabled that company to pay a huge sum of money to Pacific Microsonics for their HDCD algorithm in 2000. Microsoft then promptly deep-sixed the technology and dropped Windows playback support for the format in short order.

Tidal, who had made their name on ‘high resolution’ MQA Audio, indicated that on July 24, 2024, they were replacing all of the music in TIDAL’s MQA catalog with FLAC versions.

2023 - In August, Avid Technolgies is taken private in a USD $1.4B deal. The Burlington, MA company known for it Media Composer broadcast production editor and Pro Tools audio software will now be owned by STG Capital, a private equity firm based in California.

2023 - PS Audio debuts a new version of their high-end speaker at the AXPONA audio show in April, near Chicago, IL. It receives quite the industry comment.

2023 - In September, Parks Audio decommissions the Puffin in favor of the Waxwing, which has similar architecture inside but moved to a wireless-app-based controller.

2023 - Mastering engineer Bob Ludwig stops taking orders for new work on June 30, 2023, and will wind down his existing projects through the end of the year. Formerly of A&R, Sterling Sound, and Masterdisk NYC, he founded Gateway Mastering Studios in Portland, ME in 1992, which he operated for 30 years.

One of his most famous early cuttings by Ludwig was the Led Zepplin II album in 1969, which the band desired to be “the loudest record in the world.” His new Neumann SX-68 cutting head, the first to be helium-cooled, helped him meet the band’s wishes.

Bob is in the rarified league of mastering engineers that include Bernie Grundman; Ted Jensen, and Greg Calbi of Sterling Sound; the late Doug Sax of The Mastering Lab; the late George Piros of Fine Sound, Fine Recording, and Atlantic Records; the late George Marino of Record Plant and Sterling Sound; and numerous others.

2023 - Audio Research, the original company founded in the greater Minneapolis area by William Z. Johnson in 1970, is dissolved and refounded as a new entity, similar in concept to the GM bankrupcy and creation of the “New GM” in 2009. https://trackingangle.com/features/valerio-cora-of-acora-acoustics-corporation-to-lead-new-corporation-for-audio-research-brand. https://www.ecoustics.com/news/audio-research-acquired-2023/. TAA editor ETD conducted an extensive interview including photos with WZJ in a 1975 TAA issue.

2024 - On January 15, Darlington Labs introduces a refreshed MP and MM lineup on their website, including the new top-of-the-line MP8B, fully loaded, for $999, a revised MP7B, and MM6B, featuring higher rail voltages, enhanced power supply technology, and more. The MM5 also updated but moved to eBay only as an MM5A, derived from the MM6B but with no user adjustments. It is intended to meet the company’s committment to new or entry-level audiophiles with a USD $199 offering.

2024 - Anthony ‘Tony’ Cordesman passed away on January 29th, at age 84. Longtime AUDIO magazine reviewer, Stereophile reviewer from the mid-1980s to 1992, with TAV (The Audiophile Voice, fromer AUDIO editor (1973-1995) Gene Pitts’s follow-on magazine founded in 1995, and with The Absolute sound from 1992 through 2023. He was better known to the non-audio community as a distinguished military and political analyst first receiving widespread video coverage in the 1991 Gulf War.

2024 - On May 23rd, the Boston-area electronics retailer You-Do-It Electronics, in business for 75 years, announced its intention to close its doors and sell through their remaining inventory. In business since 1949 (as a radio and TV repair shop in Boston’s South End, and, since 1965, at the current location). A staple of the independent small parts and accessories-focused electronics, it outlasted Radio Shack and decades of internet competition, and its original founder passed away in 2022, with generations of family still working actively in the business.

In the past few years, they had reintroduced a very wide selection of NOS and used vacuum tubes for sale along with classic audio and test gear. Presumably the property value of their land parcel, well-situated off I-95 in Needham and right underneath what used to be called the FM-128 radio and TV antenna towers, contributed to the decision.

In 1965, when that location was selected, Route 128 (co-signed with I-95 for a significant portion from near Braintree to the North Shore split) was only a two-lane-per-side regional highway. This was well before the ‘Massachusetts Miracle’ of the late 1970s and 1980s resting on a foundation of electronics and computers in that area.

2024 - In mid-June, the music streaming service Tidal advised that next month (on July 24), they would be replacing the music all of the MQA-encoded music in their catalog with FLAC versions.

2024 - In mid-June, Rondi D’Agostino, president of Krell, passed away unexpectedly. She had recently hired a new CEO (although this had not yet been announced) as she was taking care of her ailing husband (both Dan and Rondi had remarried) and needed time away from the role. In September 2009, Dan and his family were removed from the original Krell in a shake-up by the Private Equity investors. A few years later, one of Krell’s automotive partners bought out the PE folks and reinstalled Rondi as CEO, as she was originally a co-founder of the company in 1980. Dan started his own company, Dan D’Agostino Audio Designs with its steampunk-looking architectural flavor.

2024 - Revox reintroduces the third revision of their B77 open-reel deck, the B77 MkIII.

1970 to 1989

1970 - JBL introduces the consumer L-100, the “Century”, with it’s reticulated (open-pore) foam available in painted orange, blue or black, at the Spring 1970 CES in Chicago. It appears that the L100 was the first use of shaped foam as a loudspeaker grille material. It will continue in the lineup until 1978. The very similar pro-version JBL 4310, which was in fact the direct technical predecessor (as JBL shamelessly headed into a consumer direction, under the guidance of Irving Stern their new head of marketing), will eclipse it for some discerning consumers who realized that the pro 4310 was largely the same speaker, but priced more inexpensively.

1970 - JBL introduces their JBL 4320, a two-way studio monitor. Arguably it is a direct competitor to the Altec 604 but some felt that it was a more accurate and “powerful” speaker. It was designed with Capitol Studios. Later it would be adopted as the standard studio monitor for Britain’s EMI. The 4320 gained significant market traction against the 604. JBL also introduced the smaller JBL 4310, a direct-radiator three-way studio monitor. This monitor introduced the idea of "nearfield" or “close” monitoring to the recording studio. This minimized the effects of studio acoustics and were also more suited to the coming independent or project-type studio.

1970 – D.S. Gibbs and I.M. Shaw publish a transistor RIAA phono preamp in the British magazine Practical Electronics (Nov. 1970 through March 1971) as part of the “Gemini” power amp and preamp.

It improves the bias stability of the typical 2-NPN RIAA phono preamp and reduces potential subsonic peaking. On a single 37V power supply rail, it uses a NPN ZTX107 input and a PNP ZTX531 output. The unit contains interesting and effective DC level shifting with loop EQ feedback to the emitter of Q1 and a secondary high-impedance input bias supply divider from V+ to the base of Q1. The matching power amp has complementary output transistors using the existing silicon 2N3055 NPN and newer 2N2955 PNP.

I.M. Shaw had (in July 1969 in competitor magazine Wireless World) recommended an improvement to the typical Quasi-Complementary output stage by the addition of a diode in series with the lower half. In the December 1969 ‘WW’, P.J. Baxandall (of 1952 feedback tone control fame) suggested an ingenious improvement by moving the correction diode to the small signal driver stage preceding the output transistors, and implemented it as a parallel combination of a diode, resistor and capacitor. Doing so markedly improved the crossover distortion otherwise inherent in Quasi-Complementary. This topology of “Enhanced Quasi” was used by NAIM from 1973 onward, Musical Fidelity, Bendini, and others into the 1980s (rather than a true NPN/PNP pair) due to a combination of cost factors (PNPs were originally more expensive) and/or or claimed issues with inherently imperfect matching between NPN and PNP transistors.

A Quasi-complementary output stage, whether ‘corrected’ or not, was extremely rare in new designs from 1990 forward. In 1995, Darlington Labs converted a 1971 Marantz 1060 integrated amplifier in one of our “real-world reference systems” from its stock Quasi (non-diode-corrected) to a true NPN/PNP topology, using the June 1988 AUDIO topology collection from Dan Sweeney as a guide, as well as bypassing the tone control network and moving to dual-mono power supply rectifiers and filter capacitors (and recapping). After significantly increasing the bias in order to accomodate the 1 x VBE greater diode drop, the result was a remarkable improvement with a lessening of grain and markedly more liquid and open sound. We see internet discussions praising this classic model these days and question how much better the results would be with a simple Baxandall diode correction (available as of the original release of the unit but perhaps not the pencil-down design phase) and reworking of the bias generator. A two-resistor/one TO-92 NPN combo with the NPN thermally mounted on the heatsink would effectively replace the existing tracking diodes and provide appropriate range from the existing trimmer.

The December 1970 issue of Practical Wireless has a very nice period-original Nixie-Tube digital clock design using final 7441 TTL Nixie tube drivers.

We encounter some of these daily in early 1970s Heathkit DVMs and Frequency Counters that form part of the ‘conversational pieces’ section of the Darlington Labs test suite.

1970 - Bose Corporation of Framingham, MA sues the publisher of Consumer Reports, for a 1970 speaker review article about the new (introduced in 1968) Bose 901 Series I speakers. The case takes 14 years to proceed through the Massachusetts courts, and is finally decided by the United States Supreme Court in 1984 (Bose Corp. v. Consumers Union of United States, Inc., 466 U.S. 485 (1984). Consumer Union wins the case 6 to 3 against Bose. The 901 is already into the 5th Generation (series V) by this time. Consumer Reports changes their review methodology based on this experience, some would say to provide less forthright analysis.

1970 - Loudspeaker manufacturer Infinity’s large Servo-Statik I is reviewed in Stereophile’s Vol. 2 No. 11 (Dec. 1970) issue by JGH. The Servo-Statik will be revised in 1975 and continued in the model lineup through 1978.

1971 - Modern Operational Circuit Design by John I. Smith is published in April through John Wiley & Sons on their Interscience imprint. This book will be two of the first widely known publications on op-amps, helping to usher in their entrance into audio gear.

1971 - Burr-Brown engineering staff Jerald G. Graeme and Gene Tobey collaborate with consulting editor Dr. Lawrence P. Huelsman to create “Operational Amplifiers, Design and Applications”, from McGraw-Hill. Jerald Graeme would go on to make a number of significant contributions to knowledge with some of his later papers remaining classics in the literature - concise, thoughtful, targeted, and still highly relevant.

1971 – Robert (Bob) Dobkin at National Semiconductor designs and releases the high-speed LM318 op-amp.  Because of the limitations of typical planar processes, so-called ‘Lateral PNP’ transistors had extremely low gain and low bandwidth.  The LM318 employed internal pF-sized capacitors which bypassed the slow PNP level shifters at high frequencies, and it could therefore slew at 70V/uS and remain stable. However, it did fail to settle with a first order response, featuring a bit of overshoot due to small ripples in the phase response.

This is at a time when conventional op-amps like the LM301 and LM741 had 0.5V/uS slew rate - their terrible in-signal-path low-bandwidth, low-gain lateral PNPs meant the whole chip had to be markedly slowed down so as to not oscillate. The lateral PNP, originated in 1965’s uA709, was originally veto’d by Fairchild Semiconductor’s R&D department, but those concerns were dismissed by their own design guru Bob Wildar who felt that they possessed otherwise-unique-abilities in the overall design context. Bob was proven right when Lateral PNP’s were quickly and widely adopted as an industry standard using the “six-mask planar process” in standard IC op-amp fabrication.

(Consider, however, that even WITH the planar PNPs, in the signal path i.e. ‘not bypassed’ like in the 318, the 709’s unique-but hard-to-use frequency compensation scheme meant that the 709 could operate at high gains with a remarkably high slew rate. More on this in our History section which discusses the first PS Audio “PS-I” preamp of 1975.)

The Ampex 102 open-reel mixdown tape deck featured the 318 and reportedly sounded “cleaner” than many of its competitors. The Analog Devices improved version (the AD518) would be used as the final composite output amp of the 1975 Orban 8000A Optimod broadcast processor. Composite FM, i.e., the actual stereo multiplexed signal broadcast before it is unfolded back to two independent channels, requires flat frequency response to 53kHz, an otherwise tough feat for the slow general-purpose op-amps of the day. Harris would use 3 x LM318 in their MX-15 FM broadcast exciter of the 1980s. Certain very-rare uses of the LM318 would bypass the internal input transistors, and feed an external discrete NPN pair into the chip. The Audiometrics PA-1 phono preamplifier sold by Radio Systems circa 1990 would feature this type of design, as would a mid-1980s Musical Fidelity preamplifier, and the MCI JH-110 open-reel deck.

Note that the TDA1034 of 1975, and largely similar NE5534 (a single NE5532) also feature capacitive bypassing of the slow PNPs to improve their internal frequency response, but they remain notably slower than the unique LM318. There is some evidence that the TDA1034 and later NE5534 is essentially an “improved” LM318 with design input from Rupert Neve, in the form of lower-noise front-end transistors, and slightly lower bandwidth still acceptable for audio. The 5534 shows improvement in one other less-well-known regard, and that is, a large percentage of LM318 production output has a slightly measurable “whistle” due to positive feedback and oscillation around the capacitive-bypass node of the DC lateral-PNP level shifter, which goes unnoticed in most applications. The 5534 is the only other known chip extant that offers the ability to bypass its own NPN input stage, and feed in an external pair (as in the LM318, above).

Bob Donkin would go on to design the LM317 voltage regulator in 1976, and was one of the co-founders of semiconductor company Linear Technology in 1981. LT did, and still does, specialize in second-source upgraded versions of industry-standard semiconductors. Not surprisingly, his design notes for the LT-manufactured “LT318A” are some of the most instructive.

1971 - The Harmon Kardon Citation 11 Preamp incorporates a phono amp “designed with computer assistance”. It is a 2-transistor feedback-pair, with no separate emitter follower, and features a 1 megohm resistive collector load on the first stage and greater than normal dynamic range in Q1. The matching Harmon Kardon Citation 12 Power Amp is patterned on an RCA design note. Nelson Pass will later publish a MOSFET conversion of the Citation 12 in TAA in 1981.

The Citation 11 preamp will be sold through 1976, alongside the newer Citation 17 for a year, and will receive some mid-cycle updates including the addition of an additional and unbypassed 100 ohm degeneration resistor in the feedback network, intended to reduce congestion and distortion in high-level passages. J. Gordon Holt reported that H/K had a policy of continual improvement, and he felt these updates caused it to be the best sounding preamp for the discerning audio enthusiast, short of the all-tube Audio Research SP-3, in the mid-1970s.

1972 - Russell O. Hamm publishes “Tubes Vs. Transistors”, his famous Audio Engineering Society paper. It explores in detail the sound of records from the late 1960s to the early 1970s as studios are converting their old tube gear to newer solid state and IC equipment. He concludes that the older tube gear has a more consonant overload characteristic that is more pleasing to the ear. An example is discussed of an engineer bringing in Ampex vacuum tube preamps into a “modern” studio with a transistor console, and markedly improving the sound quality.

He concludes that microphone preamps and LP cutting amplifiers, two functions where mechanical transducers are directly interfaced with electronics, are the biggest beneficiaries of the older technology. Tape decks and studio line amps are less affected by the solid state degradation. Slightly less well known, he later expands and revises his remarks.  See https://forums.stevehoffman.tv/threads/been-looking-at-tube-amps-preamps-question.122127/

1972 - Audio Research introduces their SP-3 tube preamp (a modified Marantz 7 design) which includes tone controls. It becomes the first new mass-production vacuum-tube preamp after the demise of the McIntosh C-22 which was phased out the same year. A prior model (called the SP-2) appears to have one version which is entirely J-FET-based. Reader input is solicited.

When the tube-type SP-3 was phased out in 1976 in favor of their new solid-state the SP-4, the Twin-Cities area manufacturer, perhaps unintentionally, left a market opening which was soon-to-be-filled by a new competitor, Conrad Johnson, of Fairfax, VA. Two young Federal Reserve economists introduced their near-Marantz-7 clone called the PV-1 in 1977. Audio Research will relaunch with tubes in 1978 via their SP-6, which is an upgraded SP-3 with tone controls deleted, and fresh new cosmetics which set the Audio Research “look” for decades. Some commentators have called the SP-4 and SP-5 and associated solid-state power amps a ‘near-death experience’ for the company.

1972 - Mark Levinson began to produce a line of ‘ultimate home electronics’. He leveraged two young engineers: George Mayhew designed the ML-2 and ML-3 power amplifiers; and John Curl designed the JC-1 MC head-amp and JC-2 preamplifier. The products were very well received and burnished the credentials of solid-state designs.

1972 - The BBC begins using a small number of in-house engineered and produced small-format nearfield monitor called the LS 3/5A. It will be released commercially three years later.

1972 - Daniel Meyer: ‘A Super Op-Amp Preamp’ is published in The Audio Amateur, one of the first published line amplifiers using a discrete op-amp topology. It features a relatively weak class-A output stage but introduces many to the concept of differential input and VAS gain stage of the op-amp. The concept has been published since 1970 in electronics magazines, and discrete versions of the uA702 and uA709 could have been built based on the exact Fairchild published schematics. However, this TAA article raised awareness in an audio context with simple discrete functional op-amp designs.

1973 – The Shure V15-III cartridge is introduced, and ups the requirement for proper capacitive loading spec. It claims to have required as much as 400 to 500pF for flattest HF response (but see paragraph below). Later Shures, including the IV and V, specified 47K and 275pF. It is interesting to note than some, perhaps a vocal minority, of audio consumers believe the V15-III to be the sonically best Shure cartridge, using Jico replacement stylii (better than the IV and various V variants).

Note: reading the Stereophile from JGH indicates that the V15-III does NOT appear to need such a high capacitance as claimed; indeed, with 400pF, the response at 20K is down a notable amount and flatter response is shown at about 150pF. It would appear that the V15-III and the small number of 1973-era Shure carts that also specify 400 to 500pF may not actually need it. Perhaps this was related to CD-4 standards; one standard specified 100K loading as standard for a CD-4 compatible cartridge. We designed the variable capacitive loading on our MM6B, MP7B and MP8B to go up to 350pF, which, when combined with turntable and tonearm capacitance, should put you beyond 400pF, due to the relatively large number of inquires in regards to this issue.

Our current advice is: DO NOT ASSUME that the Shure specifications are correct for these models. Our units ship with 100pF and we would recommend that you start there; and increase to 150pF to start (which will put a typical installation around 220pF to 275pF). Note that 47K and 275pF is the Shure recommendation for the V15-IV and V15-V as well as Stanton’s recommendation for the 881; in the latter case we recommend 150pF in our preamps, which does not include tonearm wiring and interconnect capacitance).

1973  - Monolithic Op-Amps come on strong in consumer audio. Three notable applications include the Dynaco PAT-5 with a single LM301 per channel in a line amp (including feedback tone control networks), the Crown IC-150 preamp, which (like the PAT-5) relegate the op-amp to the line stage, and maintains a discrete RIAA phono preamp. Paul McGowan at PS audio designs a 2 x uA709 per channel passive RIAA phono preamp which will be developed and sold by mail order as PS Audio’s first product.

Mr. McGowan’s recent book “99% True” mentions an “IC Op-Amp Cookbook” from 1973 that he checked out at the local library and used to build a small cigar-box-sized phono preamp for his FM station in under two weeks. He says that he didn’t have access to the specified op-amp, and so he used the older 709C which was in stock in the radio station engineer’s desk. In his blog, Paul stated that the switch was a very fortuitous “accident” because the 709 performed so much better than the specified op-amp.

However, a key issue is that a passive RIAA implementation, as was used in PS Audio’s commercial 1975 product, was unheard-of in published IC Cookbook designs up to that time. Conceptually they existed for decades in vacuum tube form, but not as a copy and paste exercise.

The resulting Paul McGowan phono preamp sounded good on the air with adequately low background noise and allowed the station to pass the FM FCC Proof-of-Performance that was required at the time. Although the Proof technically only tested the announcer microphone channel, this recently purchased small station had so many problems with their audio chain that they’d received a visit from the FCC and were forced to tidy up the primary sources.

Paul and Stan modified it over the next few months to become a passive EQ design using 4 x 709C op-amps. In April 1975, AUDIO magazine featured the first classified ad from their new firm. Large-scale production began in the spring of 1975, after money started rolling in from orders based on the AUDIO ad. Newly edited by Gene Pitts, it was the only magazine willing to publish the ad first, then invoice the fledgling company. Stereo Review and High Fidelity required upfront payment.

The 709, released in 1965, was still unique in the mid 1970s because—after the appropriate ‘damping’ networks were connected and after the output stage was forced into Class-A, often by a 10K pulldown resistor to the negative supply rail — it featured an usually fast-slewing response and linear high frequency performance - even at very high closed loop gains…far better than general purpose op-amps. This made the 709 especially well-suited to a passive RIAA design.

Later op-amps, starting with 1967’s LM301 series, were designed primarily to be “easy to use” by engineers not familiar with the intricacies of frequency compensation. It was easy for a casual engineer to unintentionally turn the op-amp into an unhelpful, uncontrollable high-powered oscillator by mistake. However, the conventional configuration slows down their frequency response severely and decreases the resulting audio quality. Paul went so far as to say that PS Audio would not have started as a company if he had used conventional unity-gain-compensated op-amps of the day (like the LM741) because the sound would have been so uninspiring.

Bob Orban would also use the 709, in 1975, for similar reasons as the make-up amplifier for the Optimod 8000A and Orban 416A Limiter VCAs, making up gain from the single-ended FET VCA stage. He relied on the 301 in most other locations, and, like many other audio users, was forced to resistively bias the 709’s raw Class-B output stage, which had gross crossover distortion and little current limiting, into something resembling a linear amplifier. Output stage design is something that was significantly enhanced in 1967’s LM301 and later op-amps.

When Paul and Stan demo’d the original PS-I for Harry Pearson of The Absolute Sound magazine, its weaknesses became apparent. The SP-3 was still in a different league. PS Audio continued development; and in 1978 replaced it with the all-discrete, PS Audio PS-II phono preamp (reviewed by Leonard Feldman in AUDIO magazine in February 1979).

Active RIAA EQ, in the most basic form, reduces the number of IC op-amps needed in half, as compared to passive EQ. This single-IC-section-per-channel with Active RIAA would become commercially commonplace once the low-noise Signetics NE5534 was introduced in 1978.

1973 - The British NAIM Preamp uses 2 stages of nested local feedback on a 24V rail for their phono amplification. A separate moving coil step-up stage later joins the MM design.

1973 - Matti Otala publishes his 4-stage low-feedback low-TIM (“Transient Intermodulation Distortion”) design.

1973 – Harry Pearson launches the first issue of The Absolute Sound, said to be based on an editorial stance of judging audio components by listening to them against the “Absolute Sound” of live instruments.  He also became tired of waiting for JGH’s irregular Stereophile publishing schedule, where issues were sometimes nearly a year late until Larry Archibald purchased the magazine from JGH in the Spring of 1982 (with Vol. 5 No. 1).

1973 – The Harris HA-2500 op-amp series is the only true monolithic high-speed op-amp available, because Harris owned the only semiconductor process that could produce equivalent speed NPN and PNP transistors.  120V/µs slew rate and 200ns (0.2%) settling time is remarkable in a conventional voltage-feedback op-amp even today. The HA-2525 is an example, and is still in production by Intersil.  While these were rarely deployed in consumer audio applications, they did find application in modern distortion analyzers.  The Hewlett-Packard HP339A series uses these in custom-screened versions to deliver a 0.0018% THD reading when introduced in 1978, a significant step up from their earlier HP331A thru HP334A series introduced in the mid-1960s, which couldn’t do much better than 0.02 or 0.03% in practice.

Interestingly, the supposed ‘matching’ (HP 651 and similar) frequency generators of this era features extremely high THD, owing to their amplitude stabilization networks featuring series of biased diodes (!). Designed around 1964, J-FETs were not yet ready, nor semiconductor VCAs, and apparently the tried and true incandescent lamp was considered outmoded or exhibited too much “bounce” at low frequencies.

The block diagram of mating a 651 to a 334 analyzer shows a sharp-cutoff passive filter, from another manufacturer, placed in between the two HP components. The 651 and similar generators may have actually had worse THD than the previous tube-type HP200CD type oscillators which still relied on a nearly-unpowered incandescent light bulb, pioneered by HP in 1939 with their famous HP200A oscillator that started their company (and, consequently, Silicon Valley). Probing the latter HP200A deeply reveals some claims that the H/P Masters Thesis featuring said oscillator, may have, itself, been based on some prior and uncredited art.

1974 – James Solomon paper on Monolithic IC Op-Amp design is published (which itself was a requested submission from the IEEE). It is a seminal paper and remains often quoted, having laid down the basics of operation amplifiers, including a look at slewing characteristics. It simplifies the technology to a technical audience which is still learning to appreciate the intricacies of this new device. Mr. Solomon was with National Semiconductor at the time.

1974 – Threshold is founded in 1974 by Nelson Pass and René Besne, and was acquired by a large, publicly traded corporation in 1988. Besne left the company in 1991, while Pass resigned in 1992 to pursue other interests. (These blossomed into the Pass Aleph 0 amplifier and future products). Dick Olsher reviewed the Aleph 0 in Stereophile March '95, Vol. 18 No.3. Nelson Pass is interviewed in Stereophile in 1991 just prior to leaving Threshold..

1974 – The Radford HD250 and ZD22 are introduced, and use the same RIAA preamp stage in both models. It is comprised of an input PNP, output NPN which was constant current loaded, and offered push-pull NPN/PNP output, and featured bootstrapping from the output stage to the top of Q2. 50 volt rail, and a final output R/C to correct the return to zero response of F5.

1974 - Dynaco PAT-5 preamp is introduced. It uses a discrete RIAA section with a 42V rail and a 2-transistor feedback configuration, with an LM301 in the Line stage. In 1977, the PAT-5 BiFET model is introduced and moved to a single BiFET op amp per channel.

1974 - The LF355 (low power), LF356 (unity gain stable) and LF357 (externally compensated) series of FET-input op-amps is released by National Semiconductor. They use ion-implanted P-channel FETs with a second stage similar to the LM301 series. Its output stage drives unusually high capacitive loads with ease, and is ingeniously designed considering the then-conventional 6-mask planar process (which produced extremely low performance internal PNP transistors). Neumann uses this device in their SAL-74 cutting chain amplifier for disc mastering; and it continued through the VMS-82, the DMM lathe. One suspects that every DMM disc cut has passed through at least one LF356, where it is employed in the pre-distortion necessary for the Direct Metal Mastering process (see the patent).

For audio use, it slews somewhat asymmetrically but will be used to great effect by McIntosh who will deploy the LF356 extensively in the McIntosh C-32 preamp in 1977. In this application, it is run on +/-18V rails from a large power transformer and 7818/7918 regulators with small 2.2 ohm/1000uF post regulation R/C filters.

The LF356 is still in production in 2024 with applications in military and industrial use, featuring a robust input stage that will tolerate overloads and features a still-unusually low 1/f corner noise floor and low absolute noise level without using input cascoding or relying on ‘fancy’ technology. It also runs rather hot due to both the large low-noise J-FETs and the effectively Class-A output stage. Its unique output has one NPN emitter follower “on top” and multiple NPNs on bottom, driven out of phase by a J-FET phase splitter and used as active current sinks.

While the consumer-grade 356 chip is not specified to the military-grade higher-supply-rails of the LF156, most current samples of LF356 will successfully tolerate supply voltages of +/-22V or more whereas the typical TL071 will fail. We believe that the 156, 256 and 356 are produced on the same die structure with the lower end units not individually screened. Note: the voltage offset adjustment is very unique, null/balance inputs being the sources of internal constant current J-FETs sitting against the output drains from the input stage. Obscure second-source datasheets indicate that the fixed internal resistors are 7K and are effectively paralleled by two halves of the optional enternal nulling potentimeter (25K in National Semi notes, 20K to 200K in a Linear Tech second source) to V+.

1974 - Bozak introduces the 919 preamp at $950, which will be sold through 1981. It features DJ-like slider controls and two independent stacks of three-band tone control (LF, Mid and High). The excellent plug-in phono preamplifiers will come to be utilized in Bozak’s professional DJ mixer, the CMS-10-2-L shortly. It will remain an industry standard for on-location DJ mixing (and is the ‘Bozak’ referred to in 1992’s House of Pain’s rap song “Jump Around”, i.e., “grab your Bozak”). In 1983, after the CMS-10-2 is discontinued, UREI will copy the form factor and introduce a popular IC-based (TL072) DJ mixer, their Model 1620.

1975 - The BBC small-format LS 3/5A is introduced to commercial production for the public, via licenses to a small number of loudspeaker companies. It is a small-format outside-broadcast monitor which was designed primarily by BBC engineer Dudley Harwood. He would later found Harbeth Loudspeakers and begin producing this same model in the mid 1980s. It was designed in 1972 and produced in-house by the BBC at a reported development cost of one-hundred-thousand British pounds. Companies producing them during their initial run (through 2000) or later recreations include Rogers, Spendor, Harbeth, KEF, and Stirling Broadcast.

1975 – Signetics TDA1034 op-amp is introduced, the forerunner of the NE5534.. Signetics, an American IC company founded in 1961 and famous for the NE555 timer and NE565 Phase-Lock Loop, among many others, is purchased by Philips in 1975.  This technology will be used in the NE5532 (dual, unity-gain compensated), NE5534 (Single, with external compensation connections) and NE5535 (dual FET-input) op amp series which will be second-sourced to become standard op-amps in the audio world for many years. The NE5535 will slowly fade away by 1990.

1975 - In April, JGH of Stereophile reviews pre-production samples of the Infinity Servo-Static 1A redesign. Stereophile’s review samples are plagued with numerous and repeating faults, which are eventually corrected by October. He feels that it remains a top contender for best speaker.

1975 - The Harmon Kardon Citation 17 preamp features a differential discrete op-amp design, while still using the famous 5 slider EQ that was pioneered in the Citation 11. Somewhat strangely, the HF center frequency is shifted sharply downward from the 11; one wonders if it’s primary purpose was to “dip” some of the expected HF ‘glare’ from the new design. In our opinion, the McIntosh C-32 and C-33 preamps will feature the most musically-useful 5 band EQ center points, designed by Roger Russell (then of McIntosh) and discussed on his website. We will note the slight similarity of 1992’s Cello Pallette equalizer center points, a mostly NE5532 EQ, which was designed by Dick Burwen.

1976 - Audio Research SP-4 Transistor unit is released, replacing the tubed SP-3. It uses discrete op-amp modules operating on regulated +/-20V power supply rails. The proprietary “Analog Modules” are also used in the new Audio Research solid state power amplifiers. To the best of our knowledge, the exact internal circuitry has never been released. Old models are seen on eBay parted out for their modules to keep other legacy units running. The marketplace ultimately gave the solid state units a lukewarm reception, and magazine reviewers like JGH as well. Bill Johnson would then be reluctant to provide units for magazine review up until the mid-1980s. An interesting rebuild on an SP-4A can be found here: http://conradhoffman.com/SP4A_caps.htm

1976 – Dynaco releases the professional Mark VI Amp, a 100W/ch all-tube unit using 8417 tubes in a modified Dyna Ultralinear circuit, unusual for a mass market amplifier in 1976. It was marketed to pros and installers as a high-reliability unit, although the 8417 tubes ultimately proved to be somewhat temperamental.

1976 - Jim Leach publishes his Complementary Symmetry high power low-feedback amplifier in AUDIO magazine. It still has a following in the DIY community today, including a variant referred to as the Double-Barreled Amplifier.

1976 - Peter Snell introduces the Snell ‘Type A’ loudspeaker.

1976 - JBL introduces the JBL 4311, a replacement for the 4310. JBL had discovered that the special flat baffle of the 4310 did not contribute as much to the performance improvement as had been thought a few years earlier. The 4310 tweeter was replaced with a smaller diameter unit to increase high frequency dispersion and the crossover frequencies were modified to yield a smoother response. It will be sold until 1980.

1976 – The Audio Amateur magazine moves from the Philadelphia area up to Peterborough, NH where it will continue through its sale in 2011.  Stereophile magazine, presently located up the street from Ed Dell’s former place, will move to Santa Fe two years later.

1976 – Spectral Audio is formed.  Their first unit is the Spectral MS-ONE, introduced in 1976, and was “a radical departure from earlier premium preamplifier design and construction. Its true dual monaural topology featuring extremely fast and wideband all-FET circuitry represented an extraordinary rethinking of conventional ideas”. Innovations like its direct-coupled circuits, moving-coil-ready phono stage and independent power supplies with AC line conditioning were made possible by the use of then-esoteric devices and techniques pioneered by advanced high technology disciplines such as instrumentation and microwave. The MS-ONE launched Spectral and claimed to be “the audio maverick from Silicon Valley."

1977 - The Audio Research SP-5 Transistor unit is released, and it is a simplified version of the SP-4 but deleting the tone controls and simplifying the switching.

1977 – The Receiver Wars are in hot swing, including models such as the Technics SA-1000 330W/ch ($1800 in 1978), Pioneer SX-1980, and Realistic STA-2100 all competing for the baby-boomers burgeoning wallet and desire for high power and clean sound, but who were not ready to go to “fully audiophile separates”. Of course, some would graduate to full separates later. These receivers are still coveted 45 years on, and many still perform well (especially with an electrolytic capacitor replacement and sometimes small signal transistor replacement as certain 2SC numbers like the 2SC458 and 2SC1000 would tend to get popcorn noise and/or fail from internal corrosion).

1977 – Telarc Records is founded by Jack Renner and Robert Woods, in Cleveland, OH. Their first two releases are done Direct-To-Disc, and the next ones are using Thomas Stockholm’s Soundstream digital recording system.  In 1996, Telarc merged with another independent label, Heads Up, now a Telarc subsidiary. In late 2005 both Telarc and Heads Up were bought by Concord Records. Today both labels operate as semi-autonomous units in the Concord Music Group.  Jack Renner passed away in August 2019 at the age of 84.

1977 - Thiel is founded by Jim Thiel and Kathy Gornick in Lexington, KY.  Their linear-phase speakers represent a breakthrough in transparency, phase coherence, and accuracy of sound for some listeners.  Competitors with a similar approach to phase linearity are rare but include Vandersteen, and of course planar and electrostatic speaker manufacturers (in general…some use conventional woofers or subwoofers as part of their design).

1977 – Dynaco PAT-5 BiFET (with LF357 op-amps, an uncompensated version of the LF356) is introduced and supersedes the earlier 1974 LM301-based unit.

1977 - Bozak introduces a domestic version of their CMA-150 power amplfiier, called the 929. It sells for $1250 and will remain in the line until 1988. The home uit received backlit meters and RCA inputs on the rear.

1977 - David Berning releases the Berning P-1 preamplifier. It goes through two primary revisions, the first being a modified Marantz-7 feedback RIAA topology with an added emitter follower, all running on 210V, with an inverting low-gain line stage similar to the 1962 Heathkit AA-141-A preamp, a 100K plate loaded mu=100 tube of 6AV6-origin (1/2 of a 6EU7 in the Heathkit, and 1/2 of a 12AX7 in the Berning) capacitively coupled to a ‘AX7 cathode follower running on 290V. The ‘revised’ version of the P-1 moved to a zero-feedback 3 x 1/2 12AX7 topology with split RIAA (see the later Parasound JC-3 phono discussion). The line stage became a version of the P-channel J-FET on the bottom, running on -20V, coupled to a tube stage on the top, for ‘complementary distortion cancellation” that would be used extensively in 1979’s Berning TF-10.

1977 – Technics SA-700 and SA-800 receivers use a discrete Phono preamp with PNP input, direct coupled to NPN amp, direct coupled to PNP Emitter Follower with a 2.2K resistive load. Upper-mid-level receivers and integrated amps would deploy three-transistor per channel phono preamps during the 1970s, typically combining a 2-transistor feedback pair with a resistively-loaded emitter follower at the output to drive the RIAA feedback network, with its tremendously difficult and low-impedance HF demands. Three transistors would be considered a step-up in performance from the usual two. The 1971 Marantz 1060 integrated amp was one of the first widely available three-transistor RIAA phono preamps.

The first “modern” three transistor circuit we have found is in the General Electric 1958 Transistor Manual (Third Edition, p. 30). It is designed for the GE VR-II Variable Reluctance cartridge, and also features an integral adjustable treble control. Supply voltage is 18V with a current draw of 3.5mA, usable with 2 x 9V batteries or via supply decoupling. Two 2N508s form a conventional direct coupled feedback pair, with switching for RIAA (LP) and NARTB (Tape), together with a 2N332 as an emitter follower, located outside the feedback loop, and a 5K volume pot is directly coupled to the emitter follower forming it’s load. The wiper of the pot is the output terminal. (The 1956 mono Fisher TR-1 uses three 2N109s but uses a combination of passive and active equalization, like the GE 1955 units we discuss in our “1946 to 1969” block of text).

The text states the purpose of the emitter follower output, chosen to be outside the feedback loop, is to prevent frequency response variation due to output loading (as well as providing low output impedance). This unique output arrangement would continue through the 1964 GE phono preamp circuit of the final Seventh Edition Transistor Manual. Cartridges of the era varied much more in output level than those of the late 1960s and beyond. A level control was commonly found on solid state gear of the early to mid 1960’s, helping to negate the generally-poor overload margin of solid state design.

1977 - Conrad-Johnson is formed in the absence of any current production tube preamps after Audio Research discontinues their SP-3 in favor of the solid-state SP-4. The CJ design is a lightly modified Marantz 7 circuit for RIAA and line use but eschews any tone control circuitry.

1977 - McIntosh C32 Preamp with Single-ended PNP/NPN RIAA stage and push-pull output with global feedback. It is the last classic fully discrete phono preamp that McIntosh will sell (excepting the specialty MC step-up from 1983 to 1987), until the tube-type reissue of the C22 in 1995, and from there until the modern vinyl-resurgence era lineup. It makes liberal use of the National Semiconductor LF356 op amp in a specially-selected house-numbered version.

1977 – Technics SA-1000 receiver with 330W/ch. The SA-1000's phono equalizer quoted a super-high S/N ratio of 97 dB, and a phono input overload of 300 mV signal at 1 kHz. It “won” the power output race by spec, even though the Sansui dual-chassis G-33000 was superior in build quality and arguably drove lower impedances more adequately. Our information indicates that less than 90 were actually produced, or at least sold into the US. It uses Toshiba BJT SIP ICs that run on +/-30V, similar to those used in Yamaha M508, M512 and M916 mixers. Orders of magnitude more SX-1980s were sold in this era, although, technially, Technics appears to have “won” the single-unit receiver power war.

1977 – Counterpoint is launched with its first product: the SA-1 tube preamp, designed by Ed Semanko. Michael Elliott joined Counterpoint in 1979 to design a vacuum-tube moving-coil head amp which became the SA-2.

1977 - Theta Phono Preamp – 6DJ8 cascode design with zero feedback and passive RIAA.  Mike Moffat’s first company, prior to his starting Theta Digital in the late 1980s. 6922-based phono preamp. Tube complement is two 12AT7 and four 6922's. The design team included John Beatty. Mike Moffat is interviewed in the October 1992 Stereophile.

“The power amp was a 75W monoblock thing that sold for $700 or $800 apiece, the preamp was $700, and the head-amp was $500—in 1977. The head-amp had two Western Electric 417As in it, which was the quietest tube ever made.”

1977 – John Atkinson, future editor of Stereophile, participates in a blind listening test comparing a Quad 405 ‘current dumping’ amplifier against others.  Under test conditions, the perception of differences is reduced.  John therefore sells his Lecson amplifier, but music begins to play a lesser role in his life, for reasons unclear at first. He moves away from the Quad two years later.

1977 - Pioneer’s SX-1980 Super Receiver, a 270 W/channel unit, is Pioneer’s top entry into the large receiver category and is one of the most well-known to members of the wider public as being representative of this era.

1977 - Realistic STA-2100 receiver (a re-badged Pioneer 120W/ch unit) with Realistic Mach-1 horn speakers using a 15” woofer, horn midrange and horn tweeter represent Radio Shack’s foray into the receiver wars. Radio Shack sold substantial volumes of audio gear in this era and much of it was relatively high quality, often custom manufactured by various Far East factories including Foster Electronics.

1978 - Lampton and Zacaruias publish a DIY preamp in TAA using the new NE5534 chips (of which the TDA1034A was a Phiips/Signetics predecessor). Tantalum capacitors are in the signal path, and the regulated power supply is decoupled with 47 ohm R/C network at the output, a rather standard practice in the day.

1978 - Sansui G-33000 Super Receiver. It is actually physically two separate units, and this fact generates debate as to whether it should truly be called a “receiver”, but it did compete in the receiver marketplace. True dual-mono, it was arguably the finest “receiver” of that era.

1978 - The Yamaha NS-10 loudspeaker, designed by Akira Nakamura, is introduced. While it did not fair well commercially as a traditional audiophile speaker, it become a widely-used near-field monitor for use by recording engineers and founds it way atop many a mixing bridge or console, before it’s discontinuation in 2001.

1978 – J. Gordon Holt moves Stereophile from Pennsylvania to Santa Fe, NM with his wife Polly (aka Margaret Graham, music review editor).

1978 - Texas Instruments releases their answer to the National Semiconductor LF155 series, the TI BiFET TL062, TL072, and TL082 series of op-amps using ion-implanted P-channel J-FETs on a conventional NPN planar IC process. The quad TL084 was introduced the prior year in 1977. This series will become industry standard and is still widely used to the present day.  An enhanced technology will be developed in 1997 which will produce the TLE2071/2072 series with markedly improved specifications including full-performance internal PNP transistors, but true backward compatibility with its older sibling. The lower-cost TL051/TL052, introduced the same year, leverage some improvements from the 2071/2072, improve slightly upon the speed of the older devices, but remain on a conventional process technology with consequently lower cost.

Texas Instruments in late 2021, introduced new “High-Performance” versions of the TL071 family, with an “H” suffix (for “High Performance”). They have a specified combined maximum supply rail of 40V (+/-20V) which is higher than the 38V (+/-19V) of the TLE2071/72 family. The “H” versions also have more robust on-chip EMI and RFI ingress protection, but are only available in surface-mount (SOIC) form factors.

1978 - Audio Research gets back into the tube game after a couple of less-than-spectacularly-received solid state designs (the SP-4 and SP-5 preamps). Their new SP-6 is an SP-3 reintroduced with no tone controls and slightly modified power supplies.  Modifications continue through the SP-6F and into the beginning of what is called the SP-8.  Later models will move away from the Marantz 7-style feedback circuit into more original designs; notably their next state of the art product, the all-tube SP-10 which will be introduced in 1982. 

Audio Research will follow with the FET/Tube hybrid SP-11 in 1985, and the SP-9 in 1986, the latter claimed to be a scaled down version of the SP-11, but which is, in reality, rather different and substantially simplified, using FETs and Tubes in cascade fashion, rather than the SP-11’s Cascode design.  The SP-9 causes substantial controversy between reviewers and consumers as to its perceived quality and value; and is updated to become the SP-9 MkII in due course.

1978 – Hafler DH-101 preamp is introduced (and current through 1983). It uses two complementary BJTs in the input stage (operating common emitter), to two complementary BJTs in the output stage (operating common collector) with feedback RIAA and feedback tone controls in the line section, conceptually very similar to prior Dynaco products like the PAS and PAT series.

1979 - Kenwood introduced their DC Integrated Amplifier model KA-907. It is the scaled down version of a previous, limited-production Reference series component. The phono preamp stage utilizes a differential configuration of Large Geometry Toshiba J-FETs cascoded into BJTs, with the RIAA equalization implemented in a global feedback loop. The line amplifier featured a similar topology. Internal manual DC preset trimmers minimized DC offset and maximized headroom in each stage. Note that the amp is only truly DC-Coupled if the tone controls are bypassed.

Additionally, “DC-coupled” doesn’t actually mean response that is truly flat to DC. The response near DC still declines markedly when approaching zero Hertz, meaning that there is still phase shift associated with the feedback loops (effectively DC servos) at VLF but arguably less than would occur with true AC coupling, as well as a more stable overload recovery characteristic.

1979 - The US-based department-store retailer JC Penney (a primary competitor to Sears at that time) gets their entry into the “Super Receiver” category with their private-label, made-by-NEC MCS 3125. Rated at 125 watts per channel, it measures closer to 200WPC. The styling is diverging from the classic “all-analog” seen in the prior couple of years. It resembles a cross between a boombox and a disco floor, with over 150 LEDs on the front panel. Dual power supplies - separate for each channel - and other interesting features make it representative of a unique time in American consumer electronics.

1979 - Berning TF-10 (2N5461 P-ch FET and 12AX7) preamp. We discuss this unit in our FAQ entry. This topology will be later discontinued and the replacement TF-12 in 1988 will resume a more conventional, all-tube phono preamp stage.

1979 - In February, Leonard Feldman reviews the PS Audio PS-II phono preamp in AUDIO magazine. One of PS Audio’s first products, it replaced the original cigar-box-sized PS-I which was introduced in the back of April 1975’s AUDIO magazine and used LM709C op-amps. The PSII is very similar to the later PS IVa and PS IVb, although the newer IV versions move to active BJT current sources in the differential tail, and to LM317/LM337 based active IC regulation. Both use two high-feedback all-BJT differential discrete-op-amp gain blocks with passive RIAA EQ sandwiched in between, which will continue through the Model 4.5, 4.6 and 5.0 of the late 1980s. The later 6.0 is an op-amp model introduced after Paul McGowan has left the company (and before he later re-acquired it).

The PS-II itself had completely passive R/C filtering in the power supply. Passive power supply filtering was quoted as being “preferable for sound quality”. This was likely an artifact of the high noise level of the conventional fixed-output 7824/7924 regulators of the time directly intruding into the gain circuitry via a resistive tail load. Such a simple load offers little isolation from power supply disturbance. The existing 1976 LM317 positive (from Bob Donkin) and—at that time—forthcoming 1978’s LM337 negative (from Bob Pease) adjustable regulators, if implemented correctly, feature lower noise than the fixed 78xx/79xx series, but are still insufficient to use “bare” with a resistive tail load in a high gain circuit.

An independent reviewer comparing the PS-II to the PS-IV in 2021 noted that the II sounds more forward and more mid-centric, whereas the IV had superior dynamics and overall presentation but was rather noisy in MM mode compared to a FET-input preamp (not surprising given the large current through the BJT input pair via 2 x 22K collector loads).

1979 - An "Audio RIAA Preamplifier with No TID” is published in August by Yuri Miloslavskiji in the British Wireless World magazine. It used three transistors and was passively equalized on a 12VDC power rail.  This produced quite limited headroom. The setup instructions appear to focus on low noise biasing rather than providing maximum linearity.

1980 - Krell Industries is founded by Dan D’Agistino in 1980. They will design and manufacture a wide range of high end audio components. Eventually Dan will leave Krell and form his own company.

1980 - Roland Research is founded by Jeff Roland; Focusing on power amps to begin with, their first preamp to be offered will be the Coherence One in January 1986, an open-loop FET design that is well received.

1980 - The Sherwood S-6020CP preamp is introduced and features Large Geometry Toshiba J-FETs cascoded with BJTs. It advertised frequency response down to DC but featured coupling capacitors in the output stages of the phono preamp and the line amplifier stages.

Sherwood was reported to have outsourced design and manufacture to a far-east company named Inkel. The matching power amplifier (sold as Sherwood S-6040CP, Inkel MD2200, and LXI AM4222) was based on a circuit from the Hitachi MOSFET technical note. Note that the power amp is similar to the Hafler DH-200 and 220, but with heavier construction, a larger power supply and dual mono construction.

A matching cassette tape deck was also offered, the S-6010, which featured Dolby B and Dolby C but not yet HX-Pro. CP meant a selected “Certified Performance” unit. A visually-matching small-format receiver was also part of the lineup.

1980 – Spectral releases the DMC-10 Preamplifier which remains in production through 1990. They took the basic design concepts of the 1976 MS-ONE and rationalized them for a decade of production. This was the first known preamplifier to utilize power MOSFETs.

1980 - “Picking Capacitors” in the February and March issues of AUDIO magazine draws wider attention to the audible and measurable shortcomings of conventional capacitor implementation. Poor measured performance of tantalum and ceramic capacitors in the audio signal path is a primary finding. Capacitor distortion had been known and recognized by certain individuals and companies well back to the early to mid-1970s; Sheffield Labs having used military-grade parts in their signal chain, for sonic reasons, and Bob Orban’s 1975 Optimod 8000A purposely has zero electrolytic or film coupling caps in the signal path (although it does have two audio transformers). Certain high-end manufacturers were aware of the important of passive components — not just capacitors — but weren’t broadcasting this knowledge too widely. Edward T. Dell’s rebuild of the Dynaco Stereo 70 in Stereophile in 1966 could be considered a direct predecessor of the concept.

Some claim this article as ground-breaking. It was a dissemination of knowledge to a broader audience, being published in AUDIO rather than a technical journal (the founding history of the magazine notwithstanding, by this time it was solidly a consumer electronics magazine). The same was not universally agreed for the copious, sometimes related, separate articles on “TIM” and ‘TID’ and ‘SID’ and ‘improvements’ designed to reduce these, which were dismissed out of hand by experts like Robert Orban and Peter Baxandall. They stated that such ideas were intuitively obvious to anyone discerning and familiar with the basic operation of electronic gain stages. One critic exasperatingly regretted that ‘so much ink had been wasted’ by authors. Magazine editors had favorites, and needed content that appeared original at first glance.

Rupert Neve made widespread use of tantalum caps in most of his famous Neve transistor consoles, where, to our understanding, they were chosen more for the long-term reliability rather than for their specific sound quality. Tantalums have a relative lack of dryout compared to electrolytics, but they do have other failure modes including going noisy, and when they do fail, they often explode with gunshot-like explosive force and a terrible odor.

Engineers and musicians used to the older tube consoles were not generally impressed with solid state, although it offered significantly greater flexibility in tonal shaping and helped to augment the increasing track count of 8-track and 12-track tape machines. This extended even to non-technical folks as in this first-person story related to us in 1993 from a longtime broadcast engineer. In 1971, a local news reporter at a broadcast station complained that he didn’t like the sound of his voice on a new transistor radio console that had just replaced the old Gates Yard tube-type mixer in the news department. “Well, there isn’t really much we can do about that. It’s essentially inherent in the technology.” the engineer told the disappointed reporter.

For many years, in the 1980s and early 1990s, classified ads in broadcast magazines went looking for old tube consoles and monitor amplifiers which were often sent to the far east to be resold and/or parted out. Pre-internet, some stations were happy just to clear out space and have someone take the old, ‘outmoded’ gear off their hands.

One contributing reason to some user’s perception of a decline in overall sonic quality of the transistorized gear was likely due to the decreased quality of coupling capacitors usually electrolytic or tantalum replacing the older paper, mylar and oil-based coupling caps which were used in the higher internal impedances used in tube gear.

For example, compare the Beatles earlier releases, particularly Rubber Soul onward (all are tube) using the Studer J-37 four-track to the transistorized console and tape-machine Abbey Road LP. To our ear, and others, Abbey Road features new, deeper, tighter but less tuneful bass, a cloudier and more-reticent upper midrange, and closed-in, somewhat harsh upper frequencies and a piercing, congested sound on dynamic peaks, particularly midway through Side Two.

Geoff Emerick, the engineer for many of these sessions, had a clear fondness for tubes and noted in his book that the sound quality degradation actually changed the type of music that the band was writing. True, the older tube gear had problems including relatively high (but low-order) distortion, and soft, ill-defined bass due to extensive high-impedance R/C-decoupled power supplies, together with limited user flexibility.

But many listeners find the tube records have more “life”, “naturalness”, “musical ease”, and, counter-intuitively, open-sounding high frequencies. (Let It Be, although released after Abbey Road, was recorded in January 1969 on all Telefunken-module-based tube remote gear on the top of the EMI studio). Also compare Simon and Garfunkel releases from 1963 through 1968 Bookends, all tube, to the ‘Solid-State’ console and tape machine of the 1970 Bridge Over Troubled Waters.

Musicians and listeners fondness for early, discrete solid state recording gear is, in our opinion, a reflection more upon the late 1970s and 1980s standard of SSL (and similar) IC-based consoles using hundreds of 5534 and 5532 ICs inside, coupled with the 1980s bright (cocaine-fueled?) mixdowns and early Sony PCM multitrack technology - rather than about the early Discrete Solid State’s sound quality relative to tube-type gear. Nashville in the 1980s and early 1990s gravitated to the API line of consoles using mostly discrete op-amp design, with transformer-coupled inputs and outputs, together with the Mitsubishi X-32 Digital Multitrack machines which ran at 50.4kHz and had quite audiophile-level electronics inside. One of our long-time QC LPs was recorded on a setup of this nature, on consoles that had been (re)”wired with Monster Cable”, and cut to DMM LP on a Neumann VMS-82 cutterhead (see the October 1988 MIX Magazine) with high-end mic preamps plugged directly into the back of the X-32 tape machine and bypassing the console. We’ve found that if our designs can “sort through” this audio and make it enjoyable, they are well-suited to a tremendous variety of program material.

An even more stringent test would be the audiophile standard of “straight wire with gain”. In a case where a single unbypassed tantalum capacitor in a 75uS pre-emphasized dual-mono STL path - (Marti STL-10/R-10) - can cause audible-in-a-direct A/B test-havoc, “A” being the studio source, and “B” being a mid-level consumer-grade off-air FM stereo tuner used for talent monitoring. This otherwise very-long signal chain, encompassing dozens of op-amps and numerous electrolytic capacitors, in an actual all-analog FM broadcast station, was, after 7 years of work, finally made markedly more transparent after one single remaining tantalum capacitor per channel was excised in 1996. It was found inside and unexpectedly hidden underneath a metal RF shield in the STL-10, directly feeding the modulation-tank varactor diode, where it’s low leakage was critical to maintaining freqency stability of the non-PLL-controlled transmitter. We consider the extensive use of tantalum capacitors, particularly in Neve clone gear like 1073’s and 1084’s, as distinctly controversial, and feel that — leaving potential longevity aside — sonically they are only appropriate as compensation for otherwise-inferior solid-state circuitry, with limited headroom, on low (24V) power rails.

1980 - In April, the United States Federal Communications Commission picked the Magnavox AM stereo system as the U.S. standard, among five competing systems (from Belar, Kahn, Motorola and Harris). This decision was based on a complicated matrix of performance attributes to which the agency assigned scores, according to an individual who claimed to be an observer to the process. Leonard Kahn would sue the FCC and they would rescind the ruling, ultimately preferring to “let the marketplace decide”. The FCC later picked the Motorola C-QUAM system in 1993, which was already gaining traction in other markets including Australia and Japan, together with a transmission standard of ‘modified 75uS’ emphasis (with an additional pole at 8.7K) and a band-stop of 10K, promoted by the National Association of Broadcasters (NAB), and referred to as the AMAX standard, which is still in place today.

Broadcasters in regular AM monaural are not required to employ pre-emphasis nor band limiting, but are permitted to do so, and the vast majority do. Likewise, while very few receivers display the NAB “AMAX” certification, adoption of slightly wider IF bandwidth compared to previous designs, together with 75uS de-emphasis, became standard in many AM tuners, portables and car stereos. Modern digital signal processing (DSP) adds downward expansion, impulse noise reduction, and other processing which has become standard in automobile radios. Wideband analog tuners from the 1958 to 1961 era of combined FM-AM stereo broadcasting, other wider-band (typically) tube tuners, and high quality table radios manufactured prior to the mid 1990s, require modification to add the deemphasis or they will sound unnaturally present in the upper midrange.

1980 - Robert Orban of Orban Associates introduces the Optimod 8100 FM Limiter/Compressor/Stereo Generator, which features two-band processing with a 12dB/octave crossover at 200Hz and a distortion-cancelled clipper. It will rapidly become standard of FM stations across the nation. It’s relative lack of dynamic artifacts (spectral gain intermodulation, whereby bass transients would cause the midrange and treble to ‘duck out’ briefly) reduced listener fatigue and allowed higher average modulation levels than ever before.

At the same time, it’s built-in four-pole “phase scrambler” (phase rotator or all-pass filter) caused male voices to lose some presence, and the bass to sound rather “boxy” and “cardboard-y” on full range systems. Phase rotation effectively ‘spreads out’ transients in time, allowing a 2 to 4+dB increase in loudness for the same dynamic processing artifacts. It is very commonly employed in “popular” FM broadcasting in the USA, whether in boxes by Orban or Omnia, and almost never in “serious’ broadcasting like Classical music. The technique appears to be less widely employed in other countries including Canada and Europe, particularly Germany. Both Orban and Omnia digital boxes allow the user to engage or bypass phase rotation. Orban’s 8100XT structure, which itself was an add-on box for the basic 8100, and moved from two bands to five bands of total processing, has alternate bands in opposite polarity, for a degree of scrambling even without an overall scrambler. In the current Orban 8700 digital processor, the user can select a “purist” mode which has a linear phase crossover more akin to 1991’s Orban 4000 Transmission Limiter.

We find in commercial practice that Omnia processors on “popular music” stations appear to be running with a 400Hz phase rotator engaged, but a 5-band limiter of phase-linear design, and importantly, a treble region which is linear-phase after deemphasis. The competitor Orban products would also have a 400Hz phase rotator, but a non-linear phase crossover, and then a large phase lag in the treble after deemphasis.

Phase rotation didn’t originate with Orban; its use dates back at least to the Leonard Kahn “Symetra-Peak” processors for AM broadcast of the 1960’s, which used passive L/C lattice filters to accomplish the same goal, which was ultimately a louder broadcast within the constraints of the FCC modulation limits (note that AM has a +125% positive, -100% negative limit, whereas FM is symmetrical at +/-100% of 75kHz deviation from the assigned center frequency).

It can even be used in Public Address work to reduce feedback, but rarely is; Bill Hanley used it effectively in a troublesome venue in the Boston area in the early 1960s which had a domed roof, and before precision parametric equalization was available. Absent a highly problematic venue, many practictioners consider that it is not a ‘serious’ technique, likening the use to “destroying” the quality of the audio. We have heard it employed a couple of times in large venues and can corroborate that it tends to cause disturbance to the audience present, even a feeling of strange unease, as the result is so instantly recognizable and unnatural to the ear especially with live, relatively uncompressed speech.

Very interestingly, the original 8100A appears to have phase which “varies” the opposite way with frequency (displaying a lead from below 360Hz to above 360Hz), the exact opposite of most other modern implementations, including those of Orban digital boxes, which tend to ‘lag’ with increasing frequency. Comments welcome until we can confirm experiementally. his artifact may have been a more accurate implementation of the Kahn technique and was later changed.

Some reviewers and commentators question whether the ear is sensitive “at all” to phase., relying on, in our opinion, poorly conducted rapid blind A/B testing with inexperienced listeners. We think this is one of the most specious artguments in all of audio, and believe that the untrained public “perceives” phase in an indirect way, but functionally correlates it as being consonant with ‘clarity’ and ‘realness’. Our opinion is based on many years of real-world broadcast processing experience with feedback from announcers and the public using reproduction systems of widely varying provenance, effectively conducting real-world Blind A/B testing with thousands of listeners. Our distaste for phase abnormalities is also why we tend to design and audition using phase-coherent speaker and reproduction systems and why we normally reject subsonic filtering in phono preamp designs.

The Optimod 8100 high end had integral HF phase correction which caused the overall system pre-emphasis and de-emphasis to exhibit of large phase lag with increased frequency. This reduced the amount of high frequency clipping and limiting but caused Its high end, while clean, not to “open up” fully, always sounding a bit burnished compared to the earlier, linear-phase Model 8000A from 1975.

Shipped stock, the widely-used 8100 also included a 18dB/octave high pass filter at 30Hz, in order to protect the PLL circuits of the FM exciters from destabilizing from turntable bumps and microphone plosives. Users would have to cut PCB traces to bypass it, unlike the 8000A which had a user-solderable jumper. It may have added to the claim by Omnia, a primary competitor, that the 8100 plus add-on pre-processing boxes sounded “more like radio” and “less like real live music”.

Orban’s full-page nuclear closing salvo in a 1993 Radio World ad war said that buying their competitor’s Unity 2000 based on promised performance was like “getting down on one knee with a ring to propose to your long-time girlfriend…and she told you, sorry, she couldn’t…because marrying you would violate her parole…

The Question: How Would You Feel?

The penultimate answer, after obvious shock, confusion, and disappointment, was….

D, “Like you bought the [competitors top of the line] Unity 2000”.

In reality, the older 1975 8000A was a very purist processor, without even a single electrolytic capacitor in the signal path, so Bob had his audiophile credentials. The later dual-band 8100A was responding to radio Program Directors and their preference for a louder, more processed sound. A bit later, Mr. Orban would return to his analog purist roots with 1991’s Orban 4000 Transmission Limiter; a box intended to protect STLs and digital Satellite links.

Interestingly, the Orban company was acquired by Daysequerra in 2016, associated with high-end FM tuners. https://www.prosoundnetwork.com/business/orban-acquired-by-daysequerra

1981 - Audio Research returns to solid state with their SP-7 Solid State Preamp which is again a discrete op-amp based design.

1981 - JBL introduces the 4430 and 4435 Bi-Radial studio monitors. The 4430 will continue in the line until 1996, and the 4435 will be sold through 1999.

1981 - McIntosh introduced the C33 preamp with selected NE5534 op-amps in the phono stage, replacing the C32 with its faulty ribbon cables after only 4 years in the lineup.

An unexpected problematic design decision by McIntosh became apparent a few months after the 1977 intro of the complex C32, which relied upon a then-new plastic-laminated push-in flat ribbon cable to connect internal PCBs. These cables would prove to delaminate when exposed to prolonged heat. This failure was exacerbated by heat generated from stacking the C32 control preamp over a matching power amplifier, especially a heat-producing tube amp, a common occurrence given Mac’s success with the MC275 in 1961.

The C-33 moves from a single discrete transistor phono preamp with a CMOS-switched front end (for Phono 1 and Phono 2 switching) to two separate, now NE5534 IC-based phono preamps, which pre-amplify each directly and switch at line level. Doing so improved the specifications by eliminating the original low-level CMOS input switching network. ICs were likely used because very little additional PC board space was available; the PCBs had to fit into the C-32 form factor.

The C-33 also had revisions to the power amp which increased the power output to 20W/ch from 12W/ch. Note that the main line output and headphone outs are actually driven from the power amplifier. They also replace most of the LM301 op-amps with then-quite-new dual 4558 for less critical applications.

1982 - John Roberts’ Pheonix Systems produces the P-10 and later P-100 phono preamps. Popular Electronics published the P-10 in a DIY article; it used a truly balanced input stage and some unique circuitry. TAA will review the P-10 in 1983, with lukewarm results. John Roberts will later work for Peavey Electronics across a series of uniquely designed mid-price consoles.

1982  - The Klyne preamp is introduced, designed by Stan Klyne. The Klyne SK-5 (1988), SK-6 (1991) will follow, all based on discrete op-amp topologies. One unique twist is variable HF response correction for MC cartridges.

1982 – Another approach to a DIY zero-feedback transistor preamp is offered in Wireless World, this time on a 25V supply.  This unit places the RIAA EQ in the collector circuit of Q1.  Our testing confirms that this produces substantial loading and high distortion.

1982 - Audio Research SP-10 Tube preamp moved to 6DJ8s in place of 12AX7s; using cascode, cascade and ultralinear feedback circuitry (the latter especially prevalent in the SP11). John Atkinson (many decades later) reported that he discontinued use of his SP-10 in the early 1990’s after finding that, while the sound quality was excellent with new tubes, the tubes would degrade quickly and regularly go noisy.

1982 – The Compact Disc is released in Japan on November 1, 1982 (https://www.philips.com/a-w/research/technologies/cd/introduction.html) and will be released in March 1983 in the U.S.  The Sony model CDP-101 is the first Japanese CD player released. It is reviewed by Stereophile in January 1983 by J. Gordon Holt (JGH). https://www.stereophile.com/cdplayers/193/index.html

1983 -  The Sugden A48 MkII Solid State Amp is introduced. It was noted for its 'heavy-duty' retro approach paralleling meaty TOP3 devices (100V, 25A, 90W) and reverting to AC output coupling, the output capacitor at 10,000uF being double the value of the main 5,000uF reservoir capacitor.

It is notably similar in topology to the 1970 Kenwood KR-6160 receiver, and 1971’s Marantz 1060 integrated amplifier. These themselves bear resemblance to the various HC Lin designs from the GE Transistor manuals of the late 1950s (updated with silicon complementary output transistors). For Sugden, this arrangement, with a relatively low quiescent current, was intended to cope with the demands of low impedance loads. http://www.angelfire.com/sd/paulkemble/sound5i.html

1983 – The Hafler discrete DH-110 preamp is introduced, and is sold until 1988. It uses a slightly more complicated version of the discrete DH-101 circuitry. There will later be a simplified, all-IC version called the DH-100.

1983 - After Bozak discontinues their popular all-discrete CMS-10-2 disco/DJ mixer, UREI appears to copy the form factor and introduces their own (now-IC TL072-based) DJ mixer, the Model 1620.

After its own long model run, it will be “reborn” in a modern incarnation in the 2010s. Likewise, the Bozak will return in the 2010s via a Europe-based successor company who bought the rights to the design. This reincarnated Bozak continues to offer largely-hand-assembled models which are largely based on the all-discrete mid-1970s design, a design which runs on a tightly-regulated +40V single rail, with circuitry showing a very unique and innovative thought process that has stood the test of time.

1983 - Acoustat's Jim Strickland designs the Acoustat Trans-Nova Preamplifier, which utilizes J-FETs, and is reviewed by J. Gordon Holt in Stereophile Vol. 6 No. 3. A similar circuit will be used in the Hafler Iris in 1988 and the Hafler SE-100 in 1990.

1984 - The Acoustat 2+2 is reviewed in Stereophile’s April issue, having been in the marketplace for about a year.

1984 – Jadis is founded in France, a maker of high end vacuum tube audio gear. See: http://www.theabsolutesound.com/articles/jadis-dpmc-phono-preamplifier/ (Dick Olsher, March 2015).

1984 - In September, the founder of loudspeaker manufacturer Peter Snell passed away at the age of 38. Snell loudspeakers remain a favorite of Larry Greenhill, reviewer for Stereophile, TAA and other publications. LG reviews the Snell A/III speaker in the October Stereophile.

1984 – Steven W. Watkinson reviews the Counterpoint SA-7 preamplifier in the October Stereophile, as well as (in his judgment) the better performing Audible Illusions Modulus preamplifier.

1985 – In the July issue of Electronics and Wireless World, Richard Brice offers a Cascode Tube Phono Preamp design.

1985 - Joe Curcio offers a 6DJ8 cascode design, the Curcio Preamp, in The Audio Amateur.

1985 - Threshold introduces their FET-nine and FET-ten units.

1985 - Convergent Audio Technologies CAT SL-1 Preamp (1985) is a modified Marantz 7 and receives significant press. A thread about this design details the following attributes.

Gain is high, significant levels of global feedback are used; and complexity is high for its functionality. Some commentators said that this was very current thinking in its time frame. See https://www.diyaudio.com/forums/tubes-valves/218367-diy-cat-sl1-preamp-2.html.

“During the original time frame this was designed companies like VTL, ARC (SP-3/6), and MFA were making "improved" versions of what was essentially the Marantz 7 topology. This represented a significant improvement in performance IMO over those designs.” Note that the ARC SP-10 and SP-11 were in the CAT SL-1 mold of ‘technically complex’.

1985 - The Audio Research SP-11 Preamp is introduced, featuring innovative FET/Tube using 6DJ8s and selected 2SK117 FETs.

1985 - Superphon Revelation Basic preamplifier from Stan Warren (previously of PS Audio from 1974). See Paul McGowan interview in Stereophile in the year 2000. https://cdn.stereophile.com/content/superphon-revelation-preamplifier

1985 – Klyne is producing the SK-5, SK-4, SK-2A head-amps.

1985 – Coda Technologies is formed (although they used a different name from 1985 to 1989). Their introductory product is similar to Threshold FET-nine, FET-ten and FET-ten-e, owing in part to some of the staff being ex-Threshold employees.

1986 – National Semiconductor introduces the LM6261 series of op-amps which use a new Vertically-Integrated PNP process to inexpensively produce internal PNP transistors whose frequency response and gain approach those of the NPN devices. The LM6121 unity-gain buffer also joins the family, meant to replace the industry-standard LH0002 in form and function. Previously, an expensive process called Dielectric Isolation was needed for such a feat. Normal op-amps using the standard, less-expensive junction-isolated process had PNPs with an Ft of 10MHz vs. the NPNs of 400MHz. Other semiconductor companies will soon copy the process (Electronic Design 8/21/86, Electronic Design News 11/13/86).

1986 – John Atkinson joins Stereophile as “International Editor” in May 1986. It came out many years later that this nomenclature was actually due to issues with visas and immigration issues of the soon-to-be-former Brit.

Stereophile goes perfect-bound (Vol.9 No.4) i.e., gets a rectangular spine with labeling, and JA’s first issue is August 1986 (Vol.9 No.5) when he reviews the California Audio Labs Tempest CD player.

1986 - The Audio Research SP-9 FET/Tube Hybrid Mk I, and the revised Mk II, generates some controversy in the magazine reviewing community as to their appropriate ranking and absolute level of performance.

1987 – Conrad Johnson launches the Motif MC-7, an all-FET preamp to compete with the likes of Mark Levinson and Krell.  Reviews indicate that it outperforms the current all-tube Conrad Johnson Reference 3 preamp.  Similar circuitry will be used for a few years as the Motif brand name is phased out, and these solid state components are sold under the Sonograph (entry level) and Conrad Johnson main brands, as the CJ PF-1, PF-2, and PF-R.  The PF-1 received a rave review by Martin Colloms in the December 1990 Stereophile as providing exceptional sound and exceptional value.

1987 – Erno Borbeley publishes the Borbeley Preamplifier in Audio Amateur, designed to compete against Levinson and Krell.

1988 - David Manley founds VTL, Vacuum Tube Logic. They manufacture phono preamps, line amplifiers and power amps of all-tube design. In 1988, Stereophile reviews the VTL-300 monoblocks. VTL phono preamps of this era are near clones of the Marantz 7 design and the power amplifiers are closely related to RCA Tube Manual designs in Pentode mode, with more modern parts.

1988 - In 1988, John Curl released the SCP-2 phono preamp.

His new company was called Vendetta Research, so-named because he’d experienced fallings out with major designers who tended to simplify his purist designs - they claimed “we simplified it just enough to be practical for mass production”, but as it so happened, more than once in a legal sense, “just enough so that his actual consulting-work designs weren’t used.” Consequently, some big manufacturers didn’t see the need to pay him. Bad blood ensued. The NPD5566 dual FET, and large geometry Toshiba J-FETs such as selected 2SK146/147 were key active devices. All are long-since discontinued.

The October 1991 Berkeley Hills/Oakland CA wildfire destroyed much of the inventory and important work-in-process prototypes. As of a few years ago, he still worked on existing units and had continued developing and releasing a number of revisions for the unit. Relatively soon after, he became a longtime design consultant for Parasound.

The ‘Vendetta Research-inspired’ current Parasound JC-3 phono pre uses a combination of IC’s often used in microphone preamps (one of the first of a special class of instrumentation chips was arguably the SSM2017) combined with conventional op-amps for later stages. In our analysis, advertising copy notwithstanding, the newer JC-3 is similar to the earlier fully-discrete John Curl-produced SCP-2 only in the most general topological sense of a flat-gain input stage followed by a passive 75uS (2122Hz rolloff), leading to a second stage utilizing active EQ which accomplishes the 50Hz bass lift (‘pole’) and 500Hz shelf (‘zero’), with care and attention paid to implementation. Parasound appears to have used this for many years in other phono products such as the P/PH-100.

Today, this topology of “passive + active” is often credited by some to Erno Borbeley who in 1986 popularized it in his well-known Moving-Coil preamp design for The Audio Amateur. It has notable similarities to the 1962 Sherwood S-5000-II integrated amp phono stage, and in discrete solid state, 1956’s “First Transistor Hi-Fi Component” the Fisher TR-1 Phono preamp which used a combination of both Active and Passive RIAA EQ. The 1953 Radiotron Design Handbook 4th Ed. has an active-feedback second stage on p. 736.

The order of the sections can be reversed, with the Active 50Hz/500Hz stage first, followed by a passive 75uS rolloff and a flat gain output stage. The primary ideas are two-fold: 1) reduce the impact of a high frequency feedback loop which proves very hard to drive in a conventional active design, and 2) reduce the open-loop gain needed above 500Hz. For a 40dB preamp, two stages of 30dB gain are needed (totaling 60dB at 1kHz) when used with all-passive RIAA; using a combination “active plus passive” topology, the designer can accomplish his goal with a total of 20dB less in open-loop gain.

1988 – Krell PAM-7 preamp is introduced. The PAM-7 is the latest evolution of Krell's entry level preamplifier technology. Many of the design concepts are similar to their expensive preamplifiers and they claim are wholly unique to Krell. Two important claimed design features are dual-mono operation and the “complete absence of any capacitors in the signal path”.

1988 - Glass Audio magazine is introduced by the Audio Amateur organization which signals the official beginning of the United States vacuum-tube audio renaissance.  It is spun out of TAA which has carried some vacuum tube designs since 1970. Magazines by other organization will follow, notably in 1992 with both Sound Practices and Vacuum Tube Valley. (Both of the latter are published up through the year 2000 and remain available in PDF form). Glass Audio will be published through 2000 and then will be folded back into the renamed Audio Xpress, along with Speaker Builder which was spun out of TAA in 1980.

TAA took the name ‘Audio Electronics’ in the mid 1990s as the term Amateur, previously and positively related to Radio Amateurs and “those who do work for the love and passion of it, not for primary compensation” has become watered down in the public’s mind and moved towards a neutral or even negative connotation. We will refer to the various incarnations as simply ‘TAA’ often interchangeably throughout this text.

1988 – In May, Stereophile reviews the Mark Levinson No. 20 amplifier, which features a regulated power supply and Class-A performance to 100W into 8 ohms, together with the No. 26 preamplifier. These are new Madrigal designs (after parting ways with Mark Levinson and his engineering staff) and will be Madrigal’s last all-discrete design for a while. Leonard Feldman famously in AUDIO magazine used this amplifier to arc-weld a piece of metal together, after joining both channels together with very-high-current 0.5 ohm resistors and generating around 50 Amps peak. Doing so proved to him its robust protection as well as current delivery.

1988 - June’s AUDIO magazine features an article by Dan Sweeney that reviews twenty years of Solid-State amplifier history, with representative schematics and commentary.

1988 – In the September Stereophile, they review Chris Johnsen of The Listening Room in Boston’s self-published the Wood Effect book, discussing the importance of Absolute Polarity. https://www.stereophile.com/asweseeit/988awsi/index.html

In the actual physical hardcopy issue, there is an excellent editorial preceding it, skewering a recent article in Electronics and Wireless World in July 1988 by an English engineer, who attempts to declare subjective testing invalid. This English engineer has published a widely read series of books and consults for manufacturers including Cambridge Audio, where in our view his design ideas and topologies are clearly evident.

1988 – The Hafler DH100 uses MC33078 and NE5532 in an all-op-amp-based full-function preamplifier as their entry level offering. The Iris, introduced in the same year, will be their full-featured upscale model featuring all-discrete FET circuitry.

1988 – Hafler’s Iris Remote controlled preamp uses all-FET feedback circuitry in the RIAA and Line Amp with 4051 CMOS IC buffers and switchers and control circuitry.

The phono stage was patented as US #4,496,910. Selected J-FETs were used - 2 N-ch and 2 P-ch FETs in complementary-symmetry which fed a second complementary pair. The output is taken from the drain connections of these two, with the RIAA equalization components contained in a negative feedback loop taken from the same point. The circuit gain is increased for MC usage by bypassing one resistor that connects the input feedback point to ground. Power supply was via LM317/337 delivering +/-16V rails.

The line stage is also a complementary-symmetry J-FET. An input long-tailed-pair with a CCS source load is used. The volume control feeds the non-inverting input while negative feedback taken from the output is taken to the inverting input. Interestingly, a small amount of pre-volume-control signal is also shunted into the negative feedback path. The output is AC-coupled via a 2uF film capacitor. A J-FET mutes the audio path to ground upon power-up. Ultimately, John Atkinson found that the Iris had a “reasonably neutral line stage and a very low-noise MC phono stage”. However, despite its sophisticated and useful remote control system, the Iris was sonically bettered by the PS Audio 4.6 which used conventional BJT discrete op-amp circuitry on +/-24V rails, with two flat-gain gain blocks sandwiched around a passive RIAA network in-between.

A look at the schematic diagram makes this circuit look quite elegant, but unfortunately Stereophile reviewed the topology twice (1988 and 1990) and found it underperformed expectations.

As the circuitry of the Iris is relatively similar to that used in the Acoustat Trans-Nova FET preamp, which did impress JGH in a 1983 (Vol. 6 No. 3) review against his reference Berning TF-10 tube/FET preamp (1979), one wonders if the CMOS switching in the later models reduced the overall quality, or if JGH’s resolution or judgement in the earlier analysis was somehow less complete or rigorous as that offered by John Atkinson on the latter models.

1988 – Analog Devices develops their CB (Complementary Bipolar) 36V process which will create op-amps such as the AD825 high performance, high-speed single-SOIC op-amp, which will also be widely applied in high end audio and via upgrades.

1989 - in January, Digidesign debuts their new Sound Tools non-linear digital audio editor at NAMM. Sound Tools will become Pro Tools in 1991.

1989 - Paul McGowan (formerly of PS Audio at the time) and Arnie Nudell (ex-Infinity) form Genesis Technologies in Minturn, Colorado, a speaker company.

1989 – High Fidelity magazine ceases publication after veering substantially into Video for a number of years (and doing a good job at it). 

JA comments at some length in Stereophile about this development from one of the principal competitors. J. Gordon Holt originally wrote for High Fidelity magazine back in the late 1950s, and was frustrated at their co-mingling of editorial and advertising policy, going on to found Stereophile in Great Barrington, MA in 1962, later moving to a suburb of Philadelphia (where Ed Dell of TAA borrowed the Stereophone mailing list in 1970 and created his own magazine), and hence to Santa Fe, NM in 1978 (with TAA moving to Peterborough, NH in late 1975)..

Stereophile was then purchased by Larry Archibald in early 1982, as described in Vol. 5 No. 1, for $5,000. Publication professionalism and frequency increased markedly and went through a staggering growth phase, moving from 3,000 subscribers to more than 60,000. By relative comparison, Stereo Review and High Fidelity were around 400,000 annually and AUDIO Magazine around 100,000. Stereophile would be sold in 1998 by Larry Archibald, with JA having a smaller, non-controlling interest, to Peterson Publishing. It would then go through a series of various corporate owners. Richard Lenhert, copy editor and former music reviewer, gave an interview in July 2019 featuring recollections over the past 34 years, after his retirement.

After all those years of growth, and changes in the audio industry as well as the advent of on-line publishing, Stereophile is back down to around 40,000 subscribers and is markedly thinner than in their heyday of 25 years ago.

https://www.stereophile.com/content/must-we-test-yes-we-must-ihigh-fidelityi-dead

1989 - November’s Wireless World brings the first in a three-part series of detailed articles on 25 years history of Solid-State power amplifier developments by John Linsley Hood.

1946 to 1969

1946 - James B. Lansing’s contract with Altec expires and he goes on to create his own company, Lansing Sound. Later the name was changed to "James B. Lansing Sound". Still later, it was shortened to "JBL Sound".

1946 - Paul W. Klipsch patents a speaker that will soon be called the Klipschorn, a large folded-horn loudspeaker designed for corner placement. The enclosure housed a three-way design: separate drivers— a woofer, squawker, and a tweeter, handling the bass, midrange, and treble portions of the audio signal, respectively. It remains in continuous production to the present day, with company production headquartered in Hope, Arkansas.

1946 - Sylvania is credited with introducing the first commercial germanium diode, the 1N34, in 1946. It is still in production (in different case styles).

1946 - JBL produced the D101 15-inch loudspeaker and the model D175 high-frequency driver. The D175 would be in the JBL catalog through the 1970s. Both of these were near-copies of Altec Lansing products. The first original product was the D130, a 15-inch transducer for which a variant remained in production for the next 55 years. The D130 featured a four-inch flat ribbon wire voice coil and Alnico V magnet. Two other products were the 12-inch D131 and the 8-inch D208 cone drivers.

1947 - The Williamson Amplifier design is published in the UK, which uses a high quality output transformer and 20dB of global feedback to produce a THD rating of 0.1% at 10 watts out.

1947 – In September, RCA releases the 12AX7, a dual triode design (which combined two triodes of the high gain 6AV6 type in one envelope).  Hi-mu tubes, like the pre-octal Type 75, and small 7-pin units like the 6AT6 and 6AV6, had existed previously for the past two decades, primarily as detectors and first audio stages in radio receivers.

1948 - JBL business operations were taken over by William H. Thomas, the treasurer of Marquardt Corporation, who represented Marquardt on Lansing's board of directors, and assisted Marquardt in taking over. The company would again be largely private by the next year, and this would prove tumultuous for the original founder, James Lansing.

1948 - Columbia Microgroove Long-Playing record (using actual vinyl, rather than the earlier shellac compounds) is introduced in June as what has come to be known as the ‘LP’.

1948 - ‘Audio Engineering’ magazine is launched, later to split into AUDIO magazine and the Journal of the Audio Engineering Society.

1949 - RCA introduces the 45 RPM 7-inch record in February, their answer to Columbia’s 33 RPM 10- and 12-inch vinyl LP. RCA’s idea of making a “better” short-playing time 78 RPM disc is eventually relegated to the specialty market of singles, and Columbia’s LP will win out for longer playing albums.

In the beginning of this format war, for example, the famous Benny Goodman 1938 Carnegie Hall re-release in 1950, the first million-selling LP, was actually available in a 6 x 45 RPM stack produced by Columbia, intended for a fast record changer produced by their primary competitor. RCA had released new players which played only 78s and 45s but not 33 rpm discs, which could be considered a foreshadowing of VHS vs. Beta, or HD-DVD vs Blu-Ray or Eureka-147 vs IBOC digital broadcasting.

1949 - General Electric publishes the design of a 6SC7 preamplifier designed to accommodate the new GE VR (Variable-Reluctance) cartridge which had an output of 50mV. It features passive EQ and three turnover points - F2, F3, F4, with no F1 (50 cycle) turnover. The design uses a 68K plate load on the first stage, and a 33K plate load on the second stage, each with a matching (68K or 33K) R/C decoupling from the B+. A 200K resistor is the series feed into a combination (pre-RIAA) equalization network.  Low plate voltages are recommended.  The 6SC7 is a dual triode with an amplification factor (mu) of 70.

Why were both cathodes grounded in this design? Separate pins for the two cathodes were not available - they shared the same connection pin. In the RCA metal 8-pin series of octal tubes (introduced in 1935) pin 1 is already used in grounding the shell. And since the 6SC7 was originally intended for as an old-style phase splitter, where one triode is feeds the other stage via a shared and floating cathode connection, the single pin constraint posed no issue..

Since cathode resistors could not be used to bias either triode (and using only one would cause serious interaction between the stages), the recommendation was made for low plate voltages which assist in self-biasing (also known ‘contact bias’). Very high value grid resistors were also specified for the same reason.

The miniature 9-pin glass 12AX7, with it’s mu of 100, was one year old and not yet widely adopted. In this mono era, demanding that designers use two separate octal tubes (such as 2 6SF5s, mu=100) or two 7-pin miniature tubes (6AT6, mu=70 or 6AV6, mu=100) would have been seen as extravagant—when the intention was to promote easier adoption of the VR cartridge against other competitors who required less amplification.

The smaller 7-pin tubes were uncommon in the larger console phonographs that would have been an ideal match for this high quality VR cartridge. And the glass-envelope 6SN7, introduced in 1941 (glass case meaning that pin 1, formerly the metal shell, was now free to use as the second independent cathode) only offered a mu of 20, wholly insufficient for a phono preamp.

Audio Engineering magazine Jan. 1949 references the original GE technical note, and both are referenced in RDH4 (1953) on p. 736. The circuit also appears in the RCA 1950 tube manual RC-16. p. 276.

A similar circuit appears as the stand-alone, commercially-available GE UPX-003 Phono preamplifier which went through a number of iterations, eventually involving active EQ, and the similar Fisher PR-6 Phono preamp with slight changes, such as a 100K plate load for the second tube stage.

The octal 6SC7 tube was replaced by a 12AX7 as time went on, allowing a broader array of design choices since both cathodes of the 12AX7 were pinned out and could be biased with separate cathode resistors. Japanese manufactuers sold their own near-clones of this design, and arguably it culminated in the stereo Shure M-65 of 1962. See https://www.audioasylum.com/cgi/vt.mpl?f=tubediy&m=240540

In October 2024, Darlington Labs acquired a 1949 GE Model 45 radio-phonograph for our collection from the Albany, NY area. It includes two GE Variable Reluctance cartridges which are user-switchable via two separate interchangeable headshells (one for 78 RPM and one for 33 RPM), an integral 6SC7 magnetic phono preamp with semi-RIAA equalization (differing from the published schematics referred to above) and incorporating a separate, very-heavy monoblock 4 x 6V6GT Push-Pull-Parallel Pentode monoblock output amplifier mounted separately in the bottom of the cabinet, driving two 10-inch permanent magnet speakers. Other units in this series included one or two Jensen speakers, some of which may have had field coils. Two FM bands are included - the original 42 to 49MC and 88 to 108MC.  A sticker on the back states proudly in fancy type: "FM: The Armstrong System". Zenith and General Electric were early licensees of the Edwin Armstrong FM system.

Notes in the service manual indicate modifications developed by another engineer inside GE, on a early electrostatic photocopy, and installed by the owner in April 1957, including a 6-position phono EQ selector, full Baxandall tone control (introduced in 1952) replacing the original stepped bass and treble, and changes to the negative feedback loop adding phase compensation and broadening the HF bandwidth. Other notes indicate that various engineers were testing and competing with their various improvements in what was likely a standard unit for these gentlemen, given their employment and position. (Especially astute readers may know that HC Lin worked at GE up to 1956 when he published his famous direct-coupled transistor preamp and amplifier, taking a position with a different firm north of Boston just before the article was published in “Electronics” magazine in September 1956).

It is somewhat amusing that the 6AK5, a sharp-cutoff pentode introduced in 1940 and used in the above tuner, which was among GE’s earliest in the new ‘high-band FM”, is still today widely used among low-cost, low-quality Chinese headphone amplifiers and line amplifiers, configured as a triode. Even though it is a sharp-cutoff, more linear than a remote cutoff, the triode curves are marginal..

1949 - An Improved Williamson amplifier design is published (in America, the article is called ‘The Musician’s Amplifier’ in Audio Engineering).

1949 - D.E.L. Shorter, of the BBC Research Department, confirms that the human ear’s response to higher-order harmonics is significantly increased. This means that proper and scientifically-valid testing of distortion residuals must be “weighted” according to the ear’s natural response. Shorter propses an N^4 weighting, a second-order function which means that harmonics above the second must be increased in value by 12dB for each doubling of frequency, before summing the result in a weighted average. The prior recommendation from the Radio Manufacturers Association in 1937 proposed an N^2 function, or 6dB increase per octave. Shorter’s evaluation of the initial 1937 proposal found it directionally accurate but incomplete, and his enhancement will be further confirmed and supported by another BBC scientist in 1961 , E. R. Wigan (see our 1961 entry).

1949 - James B. Lansing commits suicide on September 4, 1949, possibly due to deteriorating business conditions, difficulty in paying supplier invoices and significant issues in shipping products. He was noted as a better engineer and inventor than a businessman. The company thereby passed into the hands of Bill Thomas, BL's vice-president.

Lansing had, remarkably and perhaps fortuitously, taken out a $10,000 life insurance policy, naming the company as the beneficiary, a decision that allowed Thomas to continue the company after JBL’s untimely personal death. Shortly thereafter, Thomas purchased the widowed Mrs. Lansing's one-third remaining interest in the company; he thereby became the sole owner. Bill Thomas is credited by many with revitalizing the company and spearheading a period of strong growth up through the late 1960s.

1951 - AES Standardization of vinyl playback EQ. It is quite similar to the future 1954 RIAA standard but without the 50Hz turnover. CCIR also publishes its equalization standard.

1951 - WFMT-FM signs on in December as a commercial FM fine arts broadcast station in Chicago, IL. Bernard and Rita Jacobs took over WOAK-FM and changed the format to 8 hours of classical music per day, with Bernard as chief engineer and Rita as primary host. WFMT, in it’s new incarnation, was one of the hundreds of new entrants to the FM band. In the next few years, most major metropolitan areas of the US would have their own commerical FM Classical or “Good Music” stations which offered a blend of Classical, Jazz, and light popular music. Bernard sold the station to WGN in 1968, who in turn donated it to the WTTW foundation. However, WFMT remained commerical in operation, airing ads which were exclusively read “live” by the on-air announcers.

WFMT outlasted classical competitors WEFM 99.5, WXFM 105.9, WFMQ 107.5, WJJD at 104.3 and WNIB 97.1 who all converted to popular formats by the 1990s. WMFT has had very high standards of technical reproduction, featured minimal audio processing, and its reputation encouraged Sony to partner with it in introducing CDs to air in a 1982 demonstration, DAT in 1987, and MiniDisc in 1992. They were an early pioneer of Dolby SR noise reduction being employed on their wired Studio to Transmitter link, whose location at the time made it impractical to reach via line-of-sight for a high-quality composite or dual-mono aural FM STL until the transmitter moved in 1995 to allow an all-digital path for the STL.

1952 - Magnetic reproducers commonly provide 10mV to 100mV output, tracking at 6 grams to 30 grams

1953 - Over 1,000,000 transistors were manufactured; in 1955, 3,500,000 transistors were manufactured, and by 1957, annual production had increased to 29,000,000 units. (http://semiconductormuseum.com/MuseumStore/TransistorMuseum_Brief_History_of_Early_Semiconductors.pdf)

A February 1953 ad from the Radio and Television News magazine states, “For the first time in history, Germanium Junction Transistors are commercially available...”. The CK722, dropping in price from over $20 in early 1953 to $1 in 1955, is likely the best remembered commercial germanium transistor.

1954 - The advent of the RIAA standard in 1954 simplified the reproduction of brand new records, and simplified the design of reproduction equipment.  It would be mirrored worldwide.

1954 - Stereo reproduction via open-reel tape is introduced to the consumer market with 7 inch reels running at 7.5 inches per second, with the professional 1/2 track format (two channels taking up all space on the tape, meaning it only played in one direction; there was no “side B”). These will later be joined by 1/4 track (side A/side B) and 3.75 ips 1/4 track options, all of which will be superceded by the improving Philips Cassette format.

Today, a handful of labels are again offering pre-recorded tapes, often through specialty tape manufacturers, focusing on 10.5” reels, 15 ips, 1/2 track. Typical prices are $300 for an album or $450 for a ‘2-LP’ set. Restored and modified open reel decks are becoming more popular among high-end consumers.

1954 - Acoustic Research, Inc. (“AR”) was founded in 1954 by Edgar Villchur and his student Henry Kloss. The AR-1 was the first commercially-successful speaker using the acoustic suspension principle which allowed extended low-frequencies from a smaller-than-expected enclosure.

The primary disadvantage was one of low efficiency, which was offset by the higher-powered tube amplifiers coming of age at this time, such as the Dynaco Mark II and other units using the Ultra-Linear output transformer winding, which provided more than double the output power versus the previous standard of a triode or triode-connected push-pull pair.

1954 - RCA publishes its famous Passive Equalization Phono Preamp design using a 7025 (an enhanced 12AX7) in its Receiving Tube Manual. The circuit retains popularity among DIY’ers and hobbyists, and is often referred to simply as the “RCA Tube Manual circuit”.

1955 - Heathkit PAM-1 preamp is introduced using the EF86 pentode input tube, bearing notable similarly to the Quad and other British preamps which also preferred the EF86 input. The PAM-1 is a companion to the W3M and W4M monoblock amplifiers which are ultralinear Williamson designs.

1955 - Saul Marantz introduces the Marantz Consolette Preamp - it is the first (mono) version of what would become the famous Marantz 7 stereo preamp in 1958.

1955 - McIntosh C8 Preamp (refined version of prior C108 preamp). One of the most complex commercial preamps dedicated to catering for the myriad of pre-RIAA equalization standards. Still considered a standard by many record collectors today.

1955 – Public demonstration of the world’s first all-transistor hifi system. http://www.ieeeghn.org/wiki/index.php/First-Hand:The_World's_First_Transistor_Hi-Fi_System. Richard (Dick) Shea of GE demonstrated his team’s 1-watt, 5-transistor (2N43s) ‘integrated amplifier’ containing a preamp, integrated volume control and power amplifier stage, all contained in a compact aluminum prototype box. This box, together with a turntable containing a GE VR-1 Variable Reluctance cartridge, was perched incongruously atop a 12” Altec Model 601 Loudspeaker in ported wooden enclosure at the front stage lip of the auditorium.

After his presentation, Dick advised the audience to be quiet, and cued up the record. The high-sensitivity loudspeaker and clean 1W of audio power filled the Irvine Auditorium in Philadelphia with the opening music of a Bach chorus, and thunderous applause ensued. One presumes that the GE team drove down the 4 hours from their Syracuse facility to the IEEE conference in Philadelphia hand-carrying gear in tow. This system had been specially designed as one integrated unit from cartridge to loudspeaker with RIAA equalization and maximally linear operation of all transistors. well before any commercially-available solutions existed, and, indeed, before most participants at the conference  believed that it could be done.

The relatively poor transistors of the time meant that they were generally relegated to small-signal applications such as hearing aids (R. Shea was hearing-impaired, and his team also created the world’s first transistorized hearing aid).

Regarding high sensitivity of loudspeakers, and what the 1-watt above would do, installers of theater systems in the 1950s and 1960s would reportedly often connect the headphone output of a portable AM radio with about 0.25W (250mW) output to one or more large speakers like the Altec VOTT (Voice of the Theater) and fill a movie theater with very loud and dynamic sound, for their own background music and enjoyment while conducting needed installation procedures and setup.

1955 – A portable-oriented 3 transistor preamp is published by R. Shea in the first (1955) edition of ‘Transistor Audio Amplifiers’. It used 2N43 and 2N44 transistors and was different somewhat from the one publicly demonstrated, and mentioned above. This first edition of the book was supported by grants from the US Air Force Army Signal Corps and the Navy Bureau of Ships, so it’s not surprising the focus is on portable applications.  A preamp design for 10mV input for 1 volt output, 60K input impedance, with F1 and F2 turnovers on RIAA curve and F3 taken care of by cartridge loading is specified, with noise at -50dB at 50 cycles, and 64dB overall gain.

1956 - Dynaco PAM-1 is introduced, the mono predecessor to the more well-known PAS-2 and PAS-3.

1956 - H.C. Lin publishes his design for a direct-coupled Transistor Power Amp using Germanium transistors. It used no interstage or output transformers and appeared simple and elegant. Lin worked for General Electric who promoted it. The design appeared, uncredited, in the GE Transistor Manual starting in 1957 (Third Edition) with enhancements in subsequent editions. Bootstrapping of the VAS was added in 1958 and the bias network gained more stability. Frequency compensation was lessened as the semiconductor complement improved.

RCA promoted a competing design using an interstage transformer-coupled driver for germanium PNP 2N2147 outputs, series stacked for higher power models (what Threshold called “Cascoded” in their 800A of 1975). This design was adopted by Fisher as well as Heathkit in 1963 for their new solid state offerings. While the RCA interstage transformer design arguably offered greater bias stability that the HC Lin, reliability still remained poor, with occasional repeated failures.

Designers converted the original Lin topology (which specified 2 Ge PNP outs, the only type practical in 1956) as soon as more reliable Silicon power transistors appeared in the mid-60s. Sherwood, for example, stuck with vacuum tubes in their S-5000 series until going all-silicon-transistor with their S-9900 and S-9500 in 1965. Dynaco followed, bringing out their famous Stereo 120 silicon solid state amp in 1966, based on a Si NPN HC Lin topology, when its only preamp was still a vacuum tube unit (the new PAS-3X, modified to drive the lower input impedance of a transistor amplifier.) Their all-transistor silicon PAT-4 preamp was introduced in 1967, wowing reviewers including JGH of Stereophile (at least for a few months).

Outfitted with the new, expensive, but relatively reliable silicon NPN output transistors, the H.C. Lin topology would begin to rule supreme into the mid-1970s, easily displacing the RCA Germanium interstage design. The last widely-known interstage transformer design was likely Radio Shack’s 1971 Realistic STA-120C receiver, replaced by the STA-120D in 1972, the D version went “full-HC-Lin” and dispensed with the transformer.

The Lin design, while initially “quasi-complementary” by necessity, was enhanced twice. I.M. Shaw in July 1969 added a power diode in series with the lower half collector (functionally the emitter). Later that year, Peter Baxandall (of feedback Tone Control fame) in December implemented a more elegant arrangement by use of a diode, resistor and capacitor in series with the lower driver. Both were published in the British “Electronics and Wireless World” magazine. Either method substantially improved the crossover characteristics and lessened crossover distortion.

By 1969, RCA was recommending a modified HC Lin topology with a differential BJT input stage, and dispensing with the traditional output coupling capacitor. This topology was used in the Harman Kardon Citation 12 and many other designs throughout the 1970s. RCA incorporated the “Baxandall Diode” improvement by 1971, but manufacturers were slower to adopt. The 1971 30-watt Marantz 1060, Sherwood 7100 series and many others didn’t add the diode until the mid 1970s or sometimes at all. As PNP Silicon power transistors became available, true complemenary outputs were added, negating the need for a Baxandall diode, and were almost always coupled with a differential (un-degenerated) BJT input stage, direct coupled outputs and a bipolar power supply.

Some manufacturers, such as NAIM and Bendini, stuck with Quasi-Complementary into the 1980s and 1990s, believing that NPN and PNP matching was not as good as a Baxandall-diode-assisted all-NPN design. Cost consideration may have also played a part, as PNP Si outputs remained more expensive for many years.

This topology - differential BJT input, single VAS, a complementary driver stage, and complementary outputs - remains the most common discrete solid stage design in production today. Enhancements were added such as active current sourcing replacing the bootstrapped VAS of the 1950s, current mirrors, and others. See Audio Magazine, June 1988, “An Informal History of Solid State Amplifiers” by Dan Sweeney. It contains an interesting overview of development from the mid 1960s to the mid 1980s with representative schematics.

1956 – Fisher introduces the first Hi-Fi transistor product (TR1 preamp). This battery-powered preamp used 2N109s, which was one of the first transistors to be made available commercially by RCA (in 1955) with an apparent focus on high-quality audio. http://web.archive.org/web/20080221051908/http://users.arczip.com/rmcgarra2/fisher.html

JGH himself reviewed the unit in the December 1956 issue of High Fidelity magazine. http://web.archive.org/web/20070208044956/http://users.arczip.com/rmcgarra2/fisher_review_12-56.gif

J. Gordon Holt discussed his first audition of the TR-1 in Stereophile Vol. 7, No,. 3, p. 4 (spring 1984) in 1958.  “I remember being completely bowled over by the sound.  It did some things far better than any tubed component I had heard, and I was so impressed by those things that I did not at first detect the things the TR-1 was doing worse than tubes.  I am confident that I would run screaming from the room were I to listen to it today, though a lot of its shortcomings were doubtless being masked by complementary shortcomings in the loudspeakers of that day.”

Specs were 20Hz to 20kHz +/-1dB, noise -60dB (re: 2mV in via low impedance cartridge).  It also offered microphone settings.  Advertised as “No microphonics and zero hum”.  It employed capacitor coupling between all three stages and used active and passive feedback and a 13.5 to 15V rail, battery powered or from a remote AC supply. JGH continued: “Soon the TR-1 was joined in a proliferation of more sophisticated and better sounding solid-state components, some of which did many things well enough that I, and the audio community at large, was confidently predicting that Lee Deforest’s little glass bottle, the clumsy old vacuum tube with its finite life and its wasteful generation of heat, would be dead and gone within 10 years (e.g. by 1968).  Twenty-five years later, the vacuum tube is not only still with us, it is enjoying a renaissance among audio perfectionists.” said J. Gordon Holt in 1984. The front cover read “Stereophile’s Almost All-Tube Issue”.   

JGH ultimately had a similar experience in reviewing the Dynaco Stereo 120 amp solid state amp in 1966, the Dynaco PAT-4 solid state preamp in 1967, and the Sony CDP-101 CD player in 1983; all received rave reviews at the time which were later toned down, then discredited, as the new and heretofore unknown distortions became known and able to be described by reviewers and listeners.

Darlington Labs after a long search acquired one of these units in January 2024.

1957 - The Tektronix 575 Transistor Curve tracer is released and is current in the Tek catalog until 1971.  Approximately 14,000 units are produced.  This unit itself contains 40 vacuum tubes and two germanium TO-3 transistors. Darlington Labs uses two restored models in our FET and semiconductor matching process, in addition to other methods of quantification, preselection and binning.  The build quality is exemplary, including extensive ceramic turrets and silver plating. It serves as a daily reminder of U.S. historical design ingenuity and build quality.

The top section header of the “Future Products” tab of our website is the interior of one of our Tek 575s. The background of the top section of the “Our Technology” tab of our website shows a panel separator (the two TO-3 Germanium transistors are on the other side, the panel being used as a heat sink) and the turret construction is visible below as you scroll down the page.

1957 – Quad ESL speaker is released by Peter Walker (later referred to as the ESL-57, and later modified as the ESL-63)..

1957 – In late 1957, the Stereo LP is introduced with Westrex 45/45 cutting system.  “The first trickle of stereo discs at the end of 1957 became a flood of them during 1958. By 1962, they were commonplace.” See Stereophile Vol. 8 No. 6, ‘Letters’, p. 16, where J. Gordon Holt gives a personal account of stereo LP release dates and availability.

1958 - The BBC publishes a research paper that defines the following goal for monaural reproduction:

“It is assumed that the ideal to be aimed at in the design of a sound reproducing system is realism, i.e. that the listener should be able to imagine himself to be in the presence of the original source of sound. There is, of course, scope for legitimate experiment in the processing of the reproduced signals in an endeavour to improve on nature, however, realism, or as near an approach to it as may be possible, ought surely to be regarded as the normal condition and avoidable departures from this state, while justified upon occasion, should not be allowed to become a permanent feature of the system.”

1958 - Higher quality magnetic reproducers for the new Stereo LP discs operate with substantially less tracking force than their mono predecessors. Stereo LPs now contained vertical as well as horizontal modulation, and sufficient compliance was needed to handle the vertical motion. The new system chosen was called the ‘Westrex 45-45’, referring to degrees in angle of cut in the groove wall, not the speed of rotation; where each stereo channel was placed on an opposite groove wall.

This system was roughly compatible with mono record players, although excessive use of mono cartridges would tend to wear the difference component more greatly than the sum component, creating “swishy” distortion when later played on a true stereo cartridge and playback system.

1958 - The GE VR-II cartridge is introduced, which was designed to be an improvement to the RPX Variable Reluctance cartridge. This was the "broadcast standard" in the US in the 60's until the Stanton 500's series took over. A detractor of the GE notes, “at which point, vinyl everywhere breathed a sigh of relief...especially the first few seconds which were always cued to death.”

1958 - GE publishes their 3-Transistor magnetic phono preamp (whose basic design continues thru the 1959, 1962, and 1964 Transistor manuals) featuring the new GE PNP low-noise germanium 2N508 transistor in a direct-coupled feedback arrangement with 2N322 acting as an output follower. A 5K potentiometer serves as the emitter load and output level control.

1958 - A hybrid Transistor/Tube Preamp GE design is published by Dwight Jones of General Electric using a 2N508 input with a 12AX7 second stage. One version of the Sherwood S-1000 amplifier used a similar circuit.

1958 - The Marantz Model 7 preamp is introduced. It is still revered today and widely copied in DIY form.  An extremely similar circuit appears in Audio Research’s SP-3 in 1973, and launches Conrad Johnson in 1977 with the PV-1 (sans tone controls). The Valve Amplification Company (VAC) introduced a hand built reissue of Marantz 7 in 1996.

1959 - Altec Lansing replaces their 604D model with the 605A Duplex at about the same price. The 605 features measured specifications which were superior to the latest prior version of the 604, and the 605As were used at EMI Abbey Road to record many of the Beatles' LPs. A senior Motown engineer reports this facility used them as monitors for many years.

However, some studios found the sound of the 605 different from the standard 604s that there was some market backlash; given the dynamics of the marketplace, this increased market acceptance of competitor JBL. Capitol Records replaced their Altec 604s with JBL D50 Monitors. Altec later re-introduced the 604 as the "E" version Super Duplex (the 605A was the first referred to as Duplex). The market for large studio monitors was beginning to diversify at least in the US.

1959 - McIntosh introduces their C-11 preamplifier.

1959 – Harman Kardon Citation I preamp, with 9 tubes, is introduced. Feedback is used around each stage, with passive RIAA in between, designed by noted engineer Stu Hegeman who favored wide bandwidth via video pentodes, output stage pentode operation and significant quantities of feedback. The Citation IV, a downscaled, more inexpensive version of the Citation I, used many of the same concepts.

1959 - Harmon Kardon introduces the Citation II power amplifier, a wide-bandwidth design. The Citation II sold for $159 in kit form or $229 assembled.

1959 - The Lafayette KT-600 stereo tube preamp is introduced, principally designed by Stu Hegeman, finished up by Aaron Newman of Lafayette. The LT-30 (KT-300 as a kit) was a mono version of the same unit. Supposedly Stu was having issues finishing up the details on the KT-600 Preamp and KT-550 pair, and they turned to an internal engineer (Stu was working as a consultant) could finish the job and they could start recouping their investment. Hegeman ended up consultng for H/K and designed the famous Citation I-V, and solid-state Citation A preamp (1962) and Citation B power amp (1964).

1959 - Fisher phono preamp tube designs employ a grounded cathode (i.e. contact bias) in the second stage of their 12AX7 circuit and thereby eliminate one cathode bypass capacitor.

1959 - Dynaco Stereo 70 amplifier, a 35W/channel tube design using EL34 outputs in ultralinear, driven by a 6AN8 combination pentode driver/triode phase splitter, is introduced.

1959 - The Marantz Model 8 stereo amplifier debuts.

1959 - Fairchild develops a planar semiconductor production process, which is used first for high reliability transistors including the first planar unit (2N1613) suitable for audio. This process is later used for monolithic ICs, being instrumental in ushering in the continued miniaturization of electronics.

1960 - McIntosh’s C-20 preamp is introduced, lasting three years in the line. It is the predecessor to the C22, which will come out in 1963 and last until 1972.

1960 - The Marantz Model 9 monophonic amplifier is introduced

1960 – In January 1960, Fairchild announced commercial release of the first silicon planar transistor technology with the 2N1613 device (which is available in quantity in April 1960). This technology was rapidly adopted by most other transistor manufacturers.

1960 – The Sherwood S-5000-II integrated amplifier is an example of a phono preamp featuring combined active and passive RIAA EQ. Their arrangement, with their use appearing to date back to 1953, employs feedback around the second tube gain stage, where it implement the 3180uS/318uS correction (50Hz pole and 500Hz zero). The 75uS (2122Hz) rolloff is accomplished passively at the output. It uses two sections of a 12AX7, each with 270K plate resistors.  Republished in Richard Shea, Amplifier Handbook 1966, McGraw Hill, p. 17-35 to 17-38.

The long-lived Tim DeParavicini 3 x 12AX7 EAR 834P design uses a similar shunt feedback to V1, the drawback being the high-impedance summing junction, which potentially can be quite susceptible to noise and hum pickup, often self-induced from a nearby unshielded power transformer. Some Chinese clones of the EAR 834 (for example, the LIttle Bear T-10 which we examined) included a 10 foot black ground wire and tell you to “clip it onto a nearby metal heating radiator.” That one didn’t even include a fuse in the AC line. Buyer beware.

1961 - Marantz releases the revised Marantz 8B stereo power amplifier, featuring upgraded output transformers of Sidney Smith’s own design and a sophisticated global feedback system with multiple capacitive trimmers to assure symmetrical HF response in the two halves of the phase splitter. Art Dudley auditioned a stock, working model in 2012 for Stereophile.

1961 - Lafayette introduces the KT-550 power amplifier, largely designed by Stu Hegeman, with a similar driver circuit to the unique Harman Kardon Citation II power amplifier.

1961 - E. R. Wigan, of the BBC Research Department, publishes a two-part article in Electronic Technology that builds upon the prior work of D.E.L. Shorter, also of the BBC, in 1949. Wigan’s new paper (split over two months) further confirms that the human ear’s response to higher-order harmonics is significantly increased. This means that proper and scientifically-valid testing of distortion residuals must be “weighted” according to the ear’s natural response. Shorter proposed an N^4 weighting, a second-order function which means that harmonics above the second must be increased in value by 12dB for each doubling of frequency, before summing the result in a weighted average. The prior recommendation from the Radio Manufacturers Association in 1937 proposed an N^2 function, or 6dB increase per octave. Shorter in 1949 evaluated the 1937 proposal, found it directionally accurate but incomplete, and enhanced it as indicated above.

Unfortunately, despite more than 87 years of scientific testing, certain self-styled “authorities” such as Audio Science Review, flatly refuse to either acknowledge, or perhaps even understand, the intricacies involved with audio testing that will be a genuine help to the consumer. The ASR SINAD factor is completely unweighted, and despite our laying out the case in great detail (and bringing receipts) in the summer of 2021, in a review of our original MM-5, the proprietor of said website remains either uninterested, uninformed, or perhaps monetarily-biased, because the units that do well in his testing are almost all high-feedback, op-amp based, conventional designs that are heavily advertised by ‘deep pockets’ large audio firms. some of whom appear to be financially incentivized via his site.

1961 - Stereo FM radio broadcasting commences in the U.S in June, using the Zenith/GE system which is backward compatible with conventional monaural broadcasting. It features full channel separation across the entire frequency range (>20dB, in comparison to competing systems, one of which is reminiscent of joint-stereo MPEG encoders and only encoded difference information in the low frequency and midrange, but not treble).

It is later adopted in Canada and Mexico with similar specs as the U.S.A, and in Europe with 50uS pre- and de-emphasis, rather than the 75uS used in North America.

This will pose a particular problem for fringe area listeners as the stereo system, compatible though it is, is 23dB noisier in stereo than mono when tuners are not pushed deep into high-RF-signal quieting. Balanced against that often-cited issue by stereo reviewers is the practical consideration that the new system continues to allow co-existing 57 KC and 69 KC SCA subcarriers—often background music or ”storecasting” for commercial establishments—which effectively pay the heat, lights and electric bills at many fledgling FM stations. FM didn’t become widely profitable until into the 1970s, and indeed, top 40 continued to be played on AM into the early 1990s (helped out partially by AM Stereo).

Detractors of the Zenith/GE FM system would be wary to remember that with another system requiring SCA to be abandoned to accommodate stereo, the FM band itself may have failed, as did the original 42-50MC FM Band.

This noisy fringe issue will eventually contribute to demands for increased modulation through sophisticated compressors, limiters and more accurate stereo generators. The idea being that with higher effective modulation, the inevitable background hiss will be less prominent. This difference will become more troublesome for 75uS regions as music gains greater high frequency content. Europe with its 50uS pre-and de-emphasis curve will be less affected.

Robert Orban will pioneer innovative ways to deal with the issue beginning with his Orban Optimod 8000 system in 1975. This is an upgrade by some to the recently-released Durroughs DAP-310 tri-band processor or the CBS Volumax and Audimax processors feeding the line level input of the external stereo generator, with their overshoot-generating 19kHz sharp filters causing the overall modulation level to be lowered about 3dB in order to keep the overshoots from the exciter’s 19kHz sharp-cutoff low-pass-filter (needed to prevent aliasing with the 19kHz FM pilot, similar to the brick-wall digital filters used in digital A/Ds) within the FCC-mandated 100% modulation limit.

The 8000A gained an average of 3dB greater total modulation for an FM station by using a phase-compensated 19kHz filter, and integrating the stereo generator with the limiter, to allow direct connection to the transmitter - bypassing unneeded line-level transformers and the typical non-phase-compenated, ‘ringing’ exciter 19K filter. It rapidly becomes a major-market standard.

Orban’s 1980 design of the Optimod 8100A used a patented distortion-cancelled clipper, which added another 2dB of loudness. The total of 5dB greater volume above the noise spelled the end of interest in Dolby FM, which was expensive, somewhat sonically incompatible, troublesome for the home listener to calibrate, and not widely available, if at all, in mobile radios, where it would have particularly been a benefit.

Automatic blend-to-mono circuitry, which is reliant on integrated circuits, would be two decades in the future. One notable attempt at improving fringe area reception, after Dolby FM had failed, occured in 1987, where the CBS CX noise reduction system of the early 80s (used on a few LPs and many Laserdiscs) was repurposed to become ‘FMX’, which purported to improve the fringe reception in the same way that dbx MTS stereo did for television in 1982. Unfortunately it dramatically increased multipath interference, as discovered in testing, and was quickly shelved.

A classical FM station just north of our facilities in Boston was instrumental in conducting FCC trials for the current FM stereo system, in combination with equipment manufacturer H. H. Scott. The station was entrusted via estate to remain playing classical music in perpetuity after the founders death, but once his trusted assistant also passed away, the station was then sold to a for-profit company. WGBH-FM in Boston shelved their long-standing classical-music format in 2009, moving to NPR talk-radio, and subsequently transferred their classical music over to this FM station which they purchased and again turned non-commercial. We will note that the station’s audio quality improved dramatically as soon as WGBH engineers took ahold of the plant. However, its output power, coverage and reach is dramatically smaller than WGBH’s main signal.

1961 - Acoustic Research (‘AR’) releases their first turntable, a manual unit with unusually high performance for the price. Its belt-drive, suspended-subchassis design will go on to inspire countless similar units including Linn. The turntable will remain available for many years.

1962 – GE revises their 3-transistor phono preamp design with NPN Silicon transistors. Now using a 2N2049 or 2N1983 input, 2N635A second stage, and a 2N1304 emitter follower output, this design produced 55dB S/N (GE 1962 Transistor manual, p. 139) using an +18V supply.

With all of these designs, the necessary input capacitor contributes to VLF phase shift. While these designs are direct coupled from Q1 to Q2, there is an electrolytic bypassing Q2’s emitter at audio frequencies, in order to develop DC feedback to the first stage. 

In broadcasting, it is well known that in order to peak uncertainty, or “bounce”, to less than a few tenths of a dB, extended low frequency response is needed, down to 0.15Hz (or 100X lower than the lowest used frequency). Otherwise low frequency phase shift will distort the waveform and cause loss of modulation when peaks are set to 100%.

This may be one additional reason why tubes were often preferred for an input stage – their inherently high input impedance enabled them to be directly coupled to the input cartridge, with no time constant from the presence of an input capacitor.  FETs can, in some cases, be used similarly, but these were rare in commercial practice.

Darlington Labs J-FET phono inputs are directly coupled, with no LF time constant present.

1962 - Harmon Kardon introduces their Citation A, a Germanium-transistor-based high-end full-function preamplifier. Stewart Hegeman, Murray Barlowe and the Citation Engineering Group are credited with the design. It is based on a master chassis and plug-in circuit cards, based on glass-epoxy boards with computer-type connectors. A 1963 Journal of the Audio Engineering Society details the design, which includes 34dB of DC and AC feedback in each gain block. A special loop on each card deals with thermal tracking and leakage problems in the Ge transistors. Notably, it also features passive RIAA EQ and regulated power supplies with a +20V, +10V and -10V rail, with individual isolation between circuit cards.

1962 – October – J. Gordon Holt founds Stereophile Magazine.  The background of this story is found in the front editorial of Stereophile Dec. 1993 (Vol. 16 No. 12, featuring ‘The Mighty CAT’ (SL-1 preamplifier) on the front cover.

1963 - Marantz C22 preamp is introduced, an update to the earlier C20. Some commentators report this as similar to the Marantz 7. While true in general, it differs in some important but subtle ways. Overall, there was substantial similarity between manufacturers of 2 and 3-tube 12AX7 style phono preamps from Marantz, McIntosh, Dynaco, Heathkit, Sherwood, Fisher, Scott, and others. Manufacturers tended to have their own twists and unique details, however. Minor but potentially important revisions were made between models and are far too numerous to detail here. The C-22 was sold from July 1963 to 1972 and moved over 6,000 units.

1963 - Germanium Transistor power amplifiers with RCA 2N2147 stacked and driver transformers are widely used by Fisher, Heathkit and others.

1964 - Harman Kardon introduces the Citation B, a 40W per channel all-silicon power amplifier, with all-NPN outputs, rated for 150V. Military and space-grade parts abound, although the power supply is completely unregulated, unlike the companion Citation A preamp. Possibly the only commercially-available solid-state power amplifier with a user-adjustable front-panel biasing setup (via preset screwdriver adjustments and calibrated by a large front-panel VU meter). It reminds one of the mid-1970s industrial look of top-of-the-line Audio Research power amplifiers. The Citation B did not appear to sell well, and is believed to be one of the rarest ‘serious’ models offered by a US manufacturer.

1964 – Semiconductor Process Engineer Dave Talbert and Robert Wildlar develop the uA702 op amp at Fairchild Semiconductor, was the first monolithic IC to be a widely-used commercial product. The first known published IC phono preamp circuit that we have found based on this IC is in 1969. The 1967 Fairchild Linear IC Applications Handbook provides an excellent overview.

1964 – GE publishes an all-NPN Silicon transistor-based RIAA phono preamplifier. It features a 2N2925 input, 2N2924 2nd stage 2N3397 or 2N2924 or 2N2925. 22V at 3.5mA.  Reprinted in Radio Electronics magazine (with modern transistor types but otherwise unchanged) in an early 1990s Ray Marston article.

Specs: 6mV in for 1V out, 0.15% THD at 1V (2dBu) which is 15dB below clipping (at +17dBu). +/-1dB from 40K to 12K with Shure M77 Dynetic cartridge. 72dB S/N A-wtd. Separately, a tape playback amp with 2N3391A is shown which is specified at 57dB S/N unweighted, 66dB weighted. Darlington Labs auditioned this design in 1996, finding that it substantially outperformed a professional broadcast preamplifier. See GE Transistor Manual, Seventh Edition, 1964, p. 257.

1964 - McIntosh C24 Transistor Preamp is introduced. This will be sold simultaneously with the existing tube C22 through 1968.

1964 - Cycles per Second (CPS) is gradually replaced by Hz (for Hertz, an electrical pioneer and inventor).

1964 – Bob Wildar develops the uA709 op amp at Danelectro which is subsequently bought by Fairchild Semiconductor.  PS Audio’s first product in 1974 will be 2 x 709C per channel phono preamp with passive RIAA. Selling commenced with an ad in the April 1975 AUDIO magazine. PS Audio will move to discrete transistors by 1979 with the PS-II phono preamp. 1967’s Fairchild Linear IC Applications Handbook has an excellent writeup on the uA709 and the uA702.

1965 - Leak’s Stereo 30 Integrated Amp (Germanium version) is introduced. It will be updated shortly to the Leak Stereo 30 Plus (Silicon); Leak Stereo 70; Leak Delta 30; and Leak Delta 70. The Delta 70 will continue through 1978. In 2020, Leak introduced a new Stereo 130 integrated amplifier which contains styling cues from these original models.

1965 - Sherwood goes “all-Silcon” with their S-9900 and S-9500 Silicon Transistor integrated amplifiers. Styled similarly to the S-5000 tube line, the Phono preamps feature NPN Silicon transistors and capacitive coupling between the stages. and high impedance direct biasing. Transistors are individually selected and binned for Hfe (current gain).

Three stages of revisions appear in the service manuals, but they prove quite reliable (we restored a 1967 sample in 2017 which needed only a complete electrolytic recapping — all original semiconductors being intact, functional and quiet, even though traces were pulling off of the early etched PCBs). The power amplifier is essentially a H.C. Lin design with an apparent anti-latching circuit for the bottom side of the output totem pole, which also may improve the crossover characteristic. The Baxandall Diode or other crossover mitigation would be three to four years in the future.

1965 - Silicon transistor technology continued to replace germanium transistor technology for most commercial, industrial and military uses – based on the excellent performance characteristics (relative to prior Germanium transistors), device consistency and manufacturability of silicon epitaxial planar process.

1966 - Neumann uses the new uA709 op-amp in their SG-66 disc cutting control amplifier of their their new VMS-66 lathe, potentially the first widely-known audio use of the chip. We note that a number of high-end separate mastering studios considered the Neumann drive electronics package to be less-excellent that the Neumann cutter heads themselves, and many would custom-modify and “home-brew’ or ‘hotrod’ their own signal path.

1966 - Dynaco Stereo 120 Power Amp (with PAS-3X with lower output impedance) is introduced.

1966 - Marantz 7T, a transistorized version of the Marantz 7, is introduced and the tube unit is discontinued. The Marantz is extremely well reviewed. Owners are reported to be less enthusiastic, with some returning their 7T models and wanting the old tubed 7 units back. Sid Smith, designer, is reported to say that he thought the 7T was the more successful design.

This will potentially foreshadow 1976’s introduction of Audio Research’s first solid-state SP-4 preamp. Salesmen at dealers anectdotally reported many newly-sold SP-4s coming back in the first week for return, many having been compared with the aural memory of the earlier AR SP-3 tubed unit which was sold from 1973. Reviewers (mostly of the Subjective-type) weren’t as enthusiastic for the SP-4, by comparison, as the earlier (mostly Objectivist-type reviewers) were for the Marantz 7T.

In retrospect, this was the era when the J-FET was becoming practical and Motorola, one of the J-FET manufacturers, had themselves in March 1966 published a passive J-FET phono preamp based on the RCA 1954 design. We surmise that the reason a J-FET was not used in the phono input stage of the 7T was due to the design efforts having begun years earlier, concerns over component availability, variability, price, or parameter change over time. The 7T topology is clever and well-executed, but in our opinion, is let down by the conventional bipolar junction transistor input, running on a very small current. In fact, germanium PNP transistors like the 2N508 produced lower noise than silicon NPN but would have been seen as old-fashioned and unreliable (probably especially by Marantz) in 1966. See the famous mid-1970s ad about a Marantz receiver than survived a house fire and was featured in an ad.

Fisher follows suit, updating its tube line to the 500-T and 400-T, most using the RCA interstage transformer Germanium circuit.

Reliability of the Germanium transistor models was reported to be mediocre to downright catastrophic, by sources that were involved in the industry. This led to an opening for the burgeoning Japanese manufacturers, who had been perfecting solid-state technology for a number of years, to move solid state away from small-signal radios and tape recorders into the integrated amplifier and receiver market, particularly coinciding with introduction of reliable silicon NPN power transistors around 1965. The Japanese components could be sold through American dealers for a much greater mark-up, and the Japanese were also reportedly willing to “push money under the table” for salesman cash incentives, as well as significant magazine advertising as well as potentially cash payments to magazine reviewers.

1966 - The KLH Model 9, designed by Arthur Janzten and released in 1960, is reviewed in Stereophile’s June issue. It will become JGH’s reference. He summarized the KLH Nine in October 1968’s Stereophile (Vol.2 No.10) in the following way: This is probably the most nearly perfect loudspeaker we have tested until this time.”

1966 - Arthur Bailey publishes an excellent 3 silicon transistor preamp in Wireless World as a companion to the “High Performance Transistor Amplifier”, (December 1966). It contains a unique, high performance DC level-shift between the first and second stages, with an emitter follower output and optional sharp cutoff LF rumble filter.

1967 - Popular Electronics December 1967 issue features the ‘Lil Tiger’ fully complementary HC-Lin-style amplifier with the newly introduced Motorola MJ470 and MJ480 complementary silicon planar output transistors in TO-126 style case. 22 Watts of Music Power is advertised, and the domestic cat sitting atop the enclosure looks both A) slightly menacing and B) quite pleased.

1967 - The Dynaco PAT-4 preamp is introduced. The phono stage runs on 20V, features 2 silicon NPN transistors and is a feedback design patterned after the PAS-3X.

1967 - Robert Widlar moves to Danelectro, which is quickly bought by National Semiconductor (from Fairchild Semiconductor) and, now working again for his old boss whom he left in a dispute over compensation, but both at a different company, creates the LM101, LM201 and LM301 series op amp.  It is a two-stage design, with active loading on the first stage.  This enables high gain with only two basic stages (plus a unity gain output).  It requires an external compensation capacitor (usually 30pF) and this is because the National Semi process cannot accommodate an on-chip capacitor. A competitor, Fairchild, will later do so the next year as the uA741.

1967 – In June, The Beatles' Sgt. Pepper's Lonely Hearts Club Band is one of the first significant non-classical LPs to be released in stereo, helping trigger the second boom in hi-fi component sales, in which the major Japanese brands dominate the mass market.

1967 – Doug Sax, Sherwood Sax, and Lincoln Mayorga open The Mastering Lab in California.  With Doug at the controls, and the all-tube signal chain designed by Sherwood, the new mastering lab will master The Doors debut album in December 1967. The operation goes on to become one of the major players in the industry, mastering 20% of the Billboard 100 by 1972.  They were also famous for Sheffield Lab audiophile recordings, producing many quality Direct to Disc LPs in the 1970s and early 1980s. Sheffield Lab started with Scully lathes and Neumann cutterheads, driven by a customized EICO HF-89 power amplifier. It ran until Doug’s death from cancer in April of 2015.  Much of the gear was purchased and moved to the US midwest for Chad Kassem’s operation.

1968 - Arnie Nudell, Cary Christie and John Ulrick found the speaker company Infinity, whose first location will be Arnie Nudell’s garage. The Servo-Statik-1 will be one of the first products to launch, to be reviewed in Stereophile in December 1970.

1968 – Dave Fullagar at Fairchild Semiconductor designs and releases the uA741 op amp, which is very closely related to the Fairchild LM101 series, but including the 30pF compensation cap on the chip, because the Fairchild process is able to accommodate the cap.  The widely-sourced 741 became the first widely-used op amp. 

However, with its internal compensation (which allowed unity gain connection without oscillation) meant that it had a unity gain frequency of only 0.5MHz.  The resultant 741 slew rate limiting caused the inability to cleanly pass a 20kHz sine wave at full output. However, because of the spectral distribution of audio (the total spectral power tends to roll off above approximately 2K) entire mixers were built with 741s in the early 1970s, and most user complaints centered on a relatively high noise level, rather than audibly-distorted high frequencies.

1968 - Radford introduces one of the first commercially-well-known Fully-Complementary-Symmetry amplifier using the NPN/PNP pair of Motorola MJ470 and MJ480 outputs. They pair it with a fully Regulated power supply using an rare thyristor (SCR)-controlled-regulator topology. In 1970, the Audio Amateur republishes a Wireless World article with a unit featuring a lightly simplified circuitry as well as a more straightforward power supply. Note our later entry under 1995 for the Woodside SC-26 preamp, as Woodside was a follow-on company from Radford, created by ex-Radford staff. To our knowledge, the reformed Woodside concentrated on vacuum-tube electronics and did not resurrect their early solid-state entries, which in our opinion, may have still had technical merit, if not a certain level of “cache”, in the 1990’s marketplace.

1968 - In October, Lee Hulko and Joe Paschek found the mastering studio Sterling Sound in NYC. It had a late-model Neumann VMS-66 (1966 being the year of it’s introduction, a tradition continued by Neumann for their future VMS-70, VMS-80 and DMM-capable VMS-82) lathe with the newest heilium-cooled Neumann SX-68 cutter head, driven by new Neumann high-power solid state amplifiers. A Neumann mastering console with equalization and dynamics control was combined with a recent Telefunken M10A tape deck which itself had a ‘preview head’. This head was physically before the main tape playback head, and fed the lathe's analog computer, which controlled groove pitch and depth based on loudness, frequency, and phase information from the musical signal. Preview heads and variable groove spacing was introduced by Neumann with an all-tube unit in 1956.

Variable spacing can be easily seen by the eye looking at the groove spacing on a wide-dynamic-range LP. It was particularly beneficial for use with the first stereo LPs in 1958. Bob Ludwig, the famed mastering engineer, left the mastering division of A&R Records and joined Sterling after he was loaned an SX-68 for demo by the Neumann distributor, but A&R wouldn’t buy one for him to keep. Bob realized that no matter how good his work, it would no longer be as competitive as other studios if those studios had the “secret weapon” SX-68. The famous LZ II pressing would be cut by Bob at Stirling the next year, and copies with the “RL” in the leadout groove fetch four figures on auctions sites currently, in good condition.

1968 – Stereophile physically downsizes to a smaller digest-format style as of 1968: Vol.2 No.8, Issue No.20, "Spring (1)," This smaller format will continue for the next 25 years through December 1993 when it moves back to full-size.

1969 – Popular Electronics magazine author Daniel Meyer publishes a discrete J-FET phono preamp article in May using Texas Instruments TIS-58 J-FETs on a 35V power supply rail, with 100K Drain and 22K Source resistor (in parallel with a large cap) together with an unbypassed resistor to set AC gain.

1969 - In August, the Woodstock Music and Arts Festival in upstate New York will feature a custom PA designed by Bill Hanley of Hanley Sound, a Boston firm. It will be powered by McIntosh tube and solid state power amplifiers, including the recently-introduced 350W tube monoblock (MI-350). Selected bass cabinets and other accessories eventually made their way to South Africa, continuing to be used commercially into the mid 1980s.

In the August 1989 BAS Speaker (the newsletter for the Boston Audio Society, available free online) there is a fascinating first-hand account from Bill who was a guest at the audio society. The 2020 book about Hanley Sound goes into substantially more detail about Hanley’s long career and exploits both before and after his most-famous gig.

1880 to 1945

“A preamplifier is utilized to amplify an input signal to a level sufficient for further amplification, either at some point remote from the original source or at such level that extraneous effects, such as noise, become insignificant. Probably the most common use for preamplifiers is in relation to phonograph or tape reproduction, and in this connection several special conditions are encountered, dictated by such factors as recording level and frequency characteristics, hum and other spurious signals, and pickup characteristics.”

- Richard F. Shea, Amplifier Handbook, Chapter 17, p. 17-34, McGraw Hill, 1966.

1880 - The technology of recording sound on a reproducible medium dates back to roughly 1880, with Emil Berliner and Thomas Edison as pioneers in the practice.

For many decades, the technology was conceptually straightforward.  Acoustical waves would be captured in the recording studio, and acoustically amplified via horn/waveguide technologies to cut a master cylinder or disc.  Playback was the reverse: Modulated waveforms in the cylinders or flat discs would be converted back into sound using a vibrating stylus mechanism coupled to an acoustical impedance transformer in the form of a horn or waveguide.

As an acoustical reproduction medium, no separate cartridges or electronic amplifiers or preamplifiers were used.

The two main physical formats were cylinders and flat discs.  Cylinders typically provided superior reproduction but were hard to manufacture in quantity.  The flat discs could be reproduced with a process similar to that which we are familiar with today (using plating of the original disc to via ‘mothers’ and ‘fathers’ to create production-ready stamper discs which pressed the final product).  Through advancements in technology and processes, the fidelity of the flat discs gradually improved to the extent that they dominated the marketplace, and cylinders faded away as a commercially-viable proposition by the mid-1920s.

1914 - In October, Edwin Armstrong is awarded a patent for his Regenerative detector circuit for radio receivers.

1915 - Peter Jensen builds (with Edwin Pridham) the first moving coil loudspeaker, using the electro-dynamic principle for which the term “dynamic speaker” was later used.

1916 - Peter Jensen builds and patents the first completely self-contained electrically-operated phonograph.

1918 – A patent is issued for the first Variable reluctance (Magnetic) cartridge.

1919 - Narrow band FM (Frequency Modulation) was demo’d by Dutch scientist and entrepreneur Hanso Idzerda. Interestingly, Hanzo was executed in 1944 after a German V2 rocket landed nearby his house, he had been warned to leave the area (and did so), but snuck back to take a more detailed look and was caught.

1920 - Commercial AM Radio broadcasting commenced with regular programming about this time. Magnetic pickup technology was patented in 1918 (and electrical cutter head technology was known in 1886).  Over-the-air playback of regular phonograph records became a common occurrence, especially in the smaller radio stations, who had more difficulty procuring and paying the top-quality live performer talent than was the practice in major metropolitan stations. 

Stations would sign on with a 250 watt transmitter, and as they built their audience and advertising base they would expand their facilities to 1kW, 5kW, and beyond, to a maximum, if permitted, of 50kW as used by the small number of assigned Clear Channel stations in the US. For a short time, in the 1930s, on a test-authorization basis, 500kW, like WLW-AM. This high-power feat would be continued on a few select FM stations above 100kW, a handful of which are still grandfathered into current FCC rules up to 320kW ERP (Effective Radiated Power) or more. By the mid 1930’s, a 250W station would be considered quite modest.

1921 - Atwater Kent begins producing his first radio components for sale, breadboard kits for construction by the user. He also introduces the complete Model 5, although in small quantities.

1922 - RCA introduces the first widely-used vacuum tube, the ‘01A directly-heated triode. This was the general purpose tube of the 1920s.

1923 - Atwater Kent introduces the Model 9 and Model 10 radios.

1924 - RCA introduces their Radiola, a Superhetrodyne-based radio receiver, using a principal invented by Edwin Armstrong. RCA would retain exclusive use of this patent until 1930.

1924 - Stereo reproduction from a single groove is patented. Samuel S. Waters, of Washington DC, was granted patent No 1520378 on 12/23/1924 (application dated 3rd July 1920) which describes a mechanical/acoustic transducer for independent operation from each groove wall.  Bell Labs worked on similar efforts from roughly 1928 through at least 1934, although patent application was delayed by the Great Depression and lack of interest by manufacturers. A particularly fine 1934 disc was loaned to the BBC in 1964 for examination. Their patent was issued in 1936. See Wireless World letters to the editor (1981). Commonly attributed solely to Blumlein in the UK in 1936 and other multi-mono groove attempts at stereo reproduction on disc.

1925 - The historical precedent for 1948’s Columbia 33 1/3 RPM record is laid when Western Electric established the format of the system which would eventually be named Vitaphone. This system used a 16 inch disc rotating at 33 and 1⁄3 revolutions per minute. This was a good practical compromise of disc size and speed. The slow speed permitted the 11-minute playing time needed to match the maximum running time of a then-standard 1000 foot film reel which was projected at 24 frames per second, and the increased diameter preserved the average effective groove velocity, and therefore the sound quality, of a smaller, shorter-playing record rotating at the then-standard speed of about 78 rpm.

These Vitaphone discs were made of a shallac compound and played with a cheap, mass-produced steel needle with a point that quickly wore to fit the contour of the groove. While it would wear out over the course of one side of play, the Vitaphone discs were recorded “inside out”. This meant that the needle was fresh during the first part of play at the inside of the record, where the effective velocity was the slowest, and would be most worn at the outside where the groove velocity was the highest.

1925 - Atwater Kent becomes the largest radio manufacturer in the United States.

1926 - This was the silent film era, where moving pictures were combined with subtitles and live orchestral or small group accompaniment in the theater. The desire for talking movies was great.  In 1926 this was made practical.  Movies went “sound” with four competing systems – the Bell Vitaphone system, which used high quality phonograph records synched up with the film, and three optical systems. The RCA system “Photophone” was an optical sound "variable-area" film exposure system, in which the modulated area (width) corresponded to the waveform of the audio signal. Two competing "variable-density" sound on film techniques were available, from Lee DeForest’s “Phonofilm”, and Fox-Case’s “Movietone”.

Due to cost considerations both in shipping extra records around and in unnecessary duplication of two competing systems for playback in every theater, the Movietone system of sound on film was dominant by the mid-1930s.

1927 - RCA introduces the UX226 vacuum tube. This new tube featured a coated filament that was designed to produce very low hum when run on AC power. Later the same year, RCA brought out the the first widely-used indirectly-heated triode, the UY227. The ‘27’s filament heated a cylinder which had metallic oxides plated on it. The filament was now called a “heater” and the cylinder or cathode was connected to a fifth pin in the base. The old directly-heated filament was no longer the primary cause of hum. The 27 made an excellent audio detector. Higher gain versions of the 27 were soon to follow in the form of the Type 37, 56, 76 (and identical but modern octal-based 6P5). This line would culminate in the 6J5 (RCA octal-based metal tube) and 6J5-GT (glass tube) single-triode and 6SN7-GT double-triode of 1941, both with a mu of 20, still popular today among audio enthusiasts with the 6SN7-GT in current production..

1927 - The Jensen Radio Manufacturing Company is founded in 1927 by Peter L. Jensen, a Danish-American engineer.

1927 - The Lansing Manufacturing Company is formed by James B. Lansing and his business partner Ken Decker. The company is to supply speaker drivers for manufacturers of console radios and separate sets. Six and eight inch models are offered.

1928 - Atwater Kent brought out their Model 40 radio. This TRF (Tuned RF) set featured 3 x 26 tubes in the gang-tuned RF stages, followed by the 27 detector. The output stage featured a 26 driving a 171 for final output. This was one of the first popular “easy operation” sets where all circuitry was encased in a metal box, no exposed wires or dangling headphones and no messy batteries. More than 1 million units were produced, with the 1-millionth given to the U.S. President Herbert Hoover.

1929 - Atwater Kent’s peak year of production, with nearly one millions radios per year being manufactured by a staff approaching 12,000, in Philadelphia.

1930 - In the United States, what had begun a decade earlier as two wavelengths time-shared as needed among stations, the AM broadcasting band now consisted of 96 frequencies from 550 to 1500 KC.

1930 - The Yankee Network of radio stations is co-founded by John Shepard (III) and his brother Robert in Boston, MA. The first two stations began a partnership in the mid 1920’s when John Shepard's Boston station WNAC was linked by equalized telco lines with Robert Shepard's station WEAN in Providence, RI. This allowed the stations to share and exchange programming on an independent basis. In 1930, those two were joined by WLBZ in Bangor, ME; WORC in Worcester, MA; WNBH in New Bedford, MA; and WICC in Bridgeport, CT, and it grew from there. The Yankee Network, which was also affiliated with CBS and later Mutual Broadcasting for national coverage, and the Yankee News Service operated until Feb. 1967.

1931 - The Moving Magnet cartridge is patented in 1931. Phonograph cartridges in this area were strictly mono (excepting experimental uses of stereo sound). Initial reproducers operated on a magnetic principal with a variable armature in between fixed coils and fixed magnets – a so-called moving iron or variable reluctance.  Lower-quality units were rubber-damped, and higher end units were oil-damped.  Oil damped models were used in professional work and better performing consumer models.

Output levels ran from 500mV (0.5V) to 5V at typical modulation, and were often fitted with a 50,000 ohm potentiometer which provided level control.

Levels were sufficiently high that consumers who owned an early radio (without phono input) could convert them for phonograph use through special adaptors which would take the place of the detector tube in the unit.  Therefore, the gain provided by a single or at most two stages of audio amplification would be sufficient to drive a loudspeaker to a useful volume.  In cases where the turntable was mounted remote from the amplifier system, lower impedance cartridges were used (providing the lower output levels around 0.5V) and a step-up transformer would be used at the far end to increase the voltage.

1931 - Performances by Leopold Stokowski and the Philadelphia Orchestra were recorded in 1931 and 1932 using wide-range equalized telco lines between the Academy of Music in Philadelphia and Bell labs facility in New Jersey.

1932 - In the 1930s and 1940s, Piezoelectric (Crystal/Ceramic) cartridges began to gain market traction, primarily due to their reduced cost.  Piezoelectric carts came in multiple levels of quality, and the output voltage was inversely proportional to output.  Inexpensive reproducers used the lowest quality with the highest output, to reduce the need for amplification.  In some cases, only minor equalization in the lower midrange was needed to flatten the response as far as was practical given the inherent limitation in the cartridge.  Output levels ranged from a few hundred millivolts to over 1 volt.

1933 - Douglas Shearer, head of the MGM Sound Reproduction department, who is dissatisfied with the loudspeakers being offered by Western Electric and the Radio Corporation of America, is determined to manufacture an improved version for his company’s professional use. John Hilliard, Robert Stephens, and John F. Blackburn were part of the team that developed the Shearer Horn. Lansing Manufacturing producing the 285 compression driver for high frequency use, and the 15XS driver is used for low (bass) frequencies. Western Electric and RCA were both contracted to build 75 units each of these models.

1933 - In December, Edwin Armstrong is granted five patents related to “wide-band” FM or Frequency Modulation. Related patent litigation on wide-band FM, fought extensively by David Sarnoff, head of RCA, would continue through Armstrong’s untimely death 21 years later, in 1954. They would eventually be successfully settled by his widow after decades of legal rangling.

1934 - Edwin Armstrong received an appointment as a professor of Electrical Engineering at Columbia, a position he held the remainder of his life, which filled the vacancy left by Professor John H. Morecroft's death.

1934 - High Fidelity comes to the AM broadcast medium, partially through efforts at existing AM stations and including new transmission frequencies from 1510 to 1600 KC. Additionally, a much higher range of broadcast frequencies known as the Apex band was introduced. Colloquially, the 1510 to 1600 KC additions and the much higher band are sometimes co-mingled or confused. Philco, as the largest radio manufacturer, introduced a high-end receiver with audio bandwidth selectable in “wide” out past 10 KC, well above the previous practical limits of AM superhetrodyne broadcast receiver design.

New transmission frequencies were opened up above 1500 KC to 1600KC although very few stations applied for and received those licenses. Priority in that new band slice was given to stations with quality equipment, which included factors such as low distortion and wideband response. Previously broadcasters had THD readings in the 10%-and-under realm (although the low-order distortion meant that the audible effect was less dramatic than we might expect today). Years later a US FCC ‘Proof of Performance’ would require full-through microphone to antenna distortion in the 2.5 to 3% THD range and a S/N of 60dB (FM); this was designed for an all-tube signal path with limited feedback and single-ended gain stages of sometimes modest linearity.

Additionally, the FCC allowed experimental testing authorization in a new “Apex Band”. These stations were assigned to "ultra-high shortwave" frequencies, approximately 25 to 44 MC. Most, but not all, employed Amplitude modulation. In AM, using a wider audio bandwidth than standard broadcast band AM stations, in order to provide high fidelity sound. In FM, using not only a 20KC audio bandwidth but also “wideband FM” whereby the modulation index was much greater than the audio frequency, for a superior Signal-to-Noise ratio. Pre-Emphasis was a key attribute of the FM system, based on the characteristics of noise vs. frequency Edwin Armstrong conducted testing using wideband FM in this Apex range, and began creating his “Yankee Network” of interlinked FM stations starting in 1936.

1935 - In this same era, Magnetic cartridges began to diverge into Moving Iron and Moving Coil.  The normal output levels decreased to 10mV to 100mV, and tracking forces ranged from 6 grams to 30 grams or more (many ounces, ie. 100 grams) in the case of some 78 rpm cartridges as attempts were made to improve both fidelity of reproduction and increase record and stylus life.

1936 - Atwater Kent ceases production of their high-quality TRF radio sets. Superhetrodyne patent protection was running out, and competitors could profitably produce much lower-cost radio, including the first of the new All-American-Five design, which dispensed with the power transformer, for even greater cost savings and often a proportional reduction in cabinet size.

1936 - Major Edwin Armstrong demonstrates long-distance high fidelity via his Yankee Radio Network in the FM band of 42 to 44MC. This high-power network, of great technical but limited financial success, would continue broadcasting through 1954, upon his death, when his wife quickly ended funding in order to continue the lawsuits against David Sarnoff and RCA, which had contributed greatly to his suicide. She eventually won all of the cases although it took until the late 1960s.

1936 - Alan Blumlein demonstrates his version of practial stereophonic recording in Great Britain at EMI.

1936 - The Shearer Horn loudspeaker is introduced with driver input from J.B. Lansing.

1937 - Avery Fisher developed a high-fidelity, wide-range console phonograph and began selling it for commercial use. Fisher Radio would have a long history of firsts in high fidelity until being sold to Sanyo in the late 1960s.

1937 - RCA introduced the connector commonly known as the RCA jack, designed for use at phono cartridge level as well as at line level, internal to its console televisions, radio and phonographs. It would subsequently adopted widely. In Europe, the term “Cinch” is used and this is based on a particular manufacturer of RCA plugs and jacks, a US-based company called Cinch, which was one of many manufacturers producing these connectors.

1937 - The US-based Federal Communications Commission (FCC) formally allocated an Apex station band, consisting of 75 transmitting frequencies running from 41.02 to 43.98 MHz. These stations remained under experimental authorization. Many relayed programming from an existing AM station although using wider bandwidth. Interestingly, this band included the first formal non-commercial status for broadcasting stations, which remains in the USA as non-commercial FM stations being preferentially allocated in the 88.1 to 91.9MHz band, although they are allowed elsewhere on the band.

1937 - The Radio Manufacturers Association (RMA) proposed an enhancement of conventional distortion testing for radio receivers and audio amplifiers, realizing that the popular new pentode output stages tended to produce distortion that was more offensive to the human ear that the simple THD metrics would indicate. RMA proposed an N^2 function, or 6dB increase per octave. D.E.L. Shorter of the BBC will evaluate the 1937 RMA proposal in 1949, during his investigation of BBC transmitter distortion issues, wherein they were facing some of the same “ears” (subjective) vs “meter” (objective) measurement inconsistencies. This work will be further continued by another yet another BBC scientist in 1961 , E. R. Wigan (see our 1949 and 1961 entries).

1937 - KGLO (AM) signed on at 1210kHz with 250 watts of daytime power, 100 watts nighttime, in Mason City, IA. The founding general manager of KGLO and Lee Broadcasting (formed by the owner of the local newspaper, the Globe Gazette) was Francis C. Eighmey. This station was the lowest-powered to be affiliated with the CBS Network but the station served what was recognized as a key market area in the Midwest. After the 1941 frequency reallocation, in March of that year, KGLO moved to 1300kHz and increased power to 1,000 watts day and night, still with a non-directional array. The transmitter was on old Highway 18 just west of Mason City. Shortly thereafter, power was increased to 5,000 watts and two flanking towers were added to produce a nighttime directional signal with nulls to the east and west, protecting other stations.

In the 1950s, this station received an FM construction permit and put KGLO-FM on the air which was well above the 100kW current maximum, designed to match the coverage of the 5kW AM signal in this part of Iowa which had excellent ground conductivity and covered a wider range than expected, extending nearly 100 miles on a good receiver. Ultimately the FM signal would not prove profitable, and the license was turned back into the FCC. Had the signal been maintained, they would have had a 250kW+ ERP grandfathered in, which may have been one of the largest in the area. In December 1984, the current owner B-Y Communications decided to get back on FM and received approval for a construction permit for an FM station on 93.5 MHz. Call letters KNIQ-FM were assigned on April 9, 1985. When KNIQ signed on in November 1985, it was only a Class-B 6kW signal and aired a pre-recorded Top 40/CHR format, without local announcers, and was based on an automation system with 10.5 inch reel tapes and a syndicated format. The recorded announcer was a Chicago FM deejay on a top-rated station in Chicago who serviced this automated format. FCC rules had changed, allowing a reduction in local origination.

On October 4, 1991, KNIQ-FM changed callsigns to KIAI-FM, flipped from CHR and recurrents to a Country format, and power was significantly increased. Then, only three weeks later, their tower collapsed in the Halloween ice storm of October 31, 1991. KIAI’s tower was not reconstructed until February, 1992 partially due to insurance claims and disputes. That tower was only one of two which collapsed in the Mason City area. The second tower to be grounded (literally) was owned by Eide Electronics, off 34th street, and contained two-way radio and paging services for much of the county. The self-standing cellular telephone tower next to the guyed unit was went down was unaffected.A second commerical FM broadcast entity was affected, as this tower also contained the transmit antenna structure for KCMR-FM. KCMR had signed on May 3, 1979, at 98.3MHz with 3kW ERP via an ERI 4-bay rototiller antenna system fed by a McMartin BF 3.5K grounded-grid transmitter, with 4CX250s in the intermediate amplifier driving a final grounded-grid 3CX3000.

In June 1990, KCMR had moved to 97.9MHz and had increased ERP to 4.5kW. In the October 31, 1991 ice storm, this falling tower had narrowly missed both the small KCMR transmitter shack as well as the racks and racks of Motorola gear in the Eide facility. The music station returned to the air on temporary FCC authority on November 3rd with two bays of the ERI salvaged and hand-welded by a 2-man crew (the father of your Darlington Labs founder and the station’s general manager) and placed on a residential-style antenna structure about 25 feet high. Local fire and police commented that they heard music for about 6 weeks before their transmit squlech muted out, as about 1kW of unexpected 98MHz was bleeding into the paging racks next door, but proved community-minded and understanding. The station’s annual fund drive started the next week, and was successful, despite the significantly-lessened coverage area. The new tower was re-erected during December 17-18, 1991. KCMR used the opportunity to upgrade to 6kW from 4.5kW with a new, more complex ERI antenna paid for mostly by the tower owner’s coverage. Luckily, the falling tower had narrowly missed the transmitter building, which had been insured separately by the radio station, and as a frugal non-profit entity, only to market value and not to replacement cost.

On September 3, 1992, the original 1979 Orban Optimod 8000A was replaced with a edge-meter Optimod 8100A. A 1985 Marti STL-10/R10 dual mono STL continued bringing unprocessed signals from the studios uptown (eventually with a 25uS pre/deemphasis), having been purchased and installed a few years earlier, after the Bell Labs breakup, when equalized telco-line prices went through the roof after deregulation. Plans had originally called for a composite STL but the station made due with telco lines initially due to a budgetary shortfall. The transmitter-located newer Orban now drove its stereo composite out to the Harris MX-15 FM exciter, itself an upgrade made a few years prior, which replaced the unreliable stock McMartin B-910 FM exciter included with the transmitter. However, while the 8100A was a clear winner in terms of decreased processing artifacts and an improvement in loudness and consistency (with it’s gated AGC platform), the phase scrambling/rotation inherent in the stock design (not easily bypassed) proved undesirable for the format. investigation into phase shift and other significant modifications to the entire plant continued through 1996. That classic unit contined to serve well until it was replaced by a Orban 2200 by 2005.

1937 - The JBL Iconic system is made for commerical use outside of MGM movie plants.

1938 - Desktop table radios from RCA began to sport “RCA” jack inputs on the rear, intended for use of an external phonograph.

1939 - Ken Decker, half of the Lansing Manufacturing Company, is killed in an airplane crash.

1940 - In this era (the late 1920s to the early 1950s) a number of methods were used to apply playback equalization in phonograph reproduction.  Some involved placing networks in the input to the vacuum tube grid, or at the output of the first stage (so called “Passive EQ”).  Others incorporated feedback networks around gain stages (so-called “Active EQ”). Certain manufacturers made the time constants variable, in order to accommodate the various record manufacturing standards.   The Radiotron Designers Handbook (1953/4) provides an excellent overview of the technologies from the 1920s up to 1953. (pp. 727 to 752).

1941 - The Lansing Manufacturing Company was bought by Altec Service Corporation, after which the name changed to “Altec Lansing.”

1941 - In the United States, the Apex band was eliminated effective January 1, 1941, in favor of Frequency Modulation in the new band of 42 to 49 MC, the “original” FM band in the US.

1941 - After the attack on Pearl Harbor on December 7, 1941, the US enters WWII. Most commercial production efforts for consumer electronics cease, with those firms facilities being dedicated to war production through 1945.

1944 - Altec Lansing produces the Altec Lansing Duplex 604 loudspeaker, which claims to be the first high-quality loudspeaker developed expressly as a studio monitor. This innovative driver has historically been regarded as growing out of the work of James B. Lansing who had previously supplied the drivers for the Shearer Horn in 1936. While the Altec 604 had a somewhat ragged frequency response, it was a significant improvement over earlier attempts; nearly all U.S. studios used it, and almost every engineer and producer was familiar with its sound and most had learned to “listen through it”. This audiophile debate by non-professionals foreshadows many more modern speaker references like the Auratone, NS-10s and others. Years later, modified Altec 604s would be used by UREI with electronic time delay equalization as the UREI Time-Aligned 813 studio monitor.

1944 - Tannoy develops their Dual Concentric Monitor which becomes a European standard for the next two decades.

1945 - In the United States, the FCC voted to move the FM broadcast band from 42 to 50MC up to 88 to 108 MC, to take effect on January 1, 1946. Political pressure had been placed upon them from David Sarnoff, general manager of RCA, being an active detractor to commercial FM broadcasting due to RCA’s broad interest in existing AM broadcasting and receivers. The FM system had already been adopted for use in the television Aural (sound) channel. Additional technical reasons for the bump-up in primary FM broadcast included ionospheric propagation: Sporadic-E skip and other anomalies which vary in an 11-year cycle, were at a minimum when the original testing and allocation was made. Environmental changes began to cause problems in the lower FM frequency band during the prior few years, and TV Channel 1 was deleted for similar reasons.