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.