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.