First-Hand:The First-Ever Integrated High Fidelity Output System
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Revision as of 13:38, 13 November 2013
Submitted by Alfred W. Barber
In 1920, I (at age fourteen) bought my first radio magazines and began to hanker for a vacuum tube to experiment with. The Radio News (August, 1920 on page 68) carried a full page ad for the Audiotron, "the first and only amateur vacuum tube licensed under Fleming. Vacuum tube patents are basic and have been sustained by the Federal Courts."
This tube sold for six dollars. My father said it was too much to spend on a hobby but I said I wanted it; I had the money and I'd never ask to buy another thing in the radio field. (I broke that promise thousands of times over.) I rode my bicycle thirty miles to buy my Audiotron.
I built a fine double tuned regenerative detector radio in my high school woodworking class and had probably the best single tube radio around. While there were several hams in the high school and I was a member of the Radio Club, I never became a ham or got an amateur license.
In 1930, I really found myself in my element. Mr. John V. L. Hogan, the inventor of the single control radio and a former assistant to Lee De Forest had a company called Radio Inventions.
When I went to Radio Inventions, the only test equipment they had was a multi-range ac-dc voltmeter. One of my first projects was to build a TV receiver having a band-pass of 50 kHz. I designed and built the receiver. However, without some kind of signal generator, I couldn't align it. When I told Mr. Hogan, he went out into the shop and brought back a tin breadbox. "You can build a signal generator in this," he said. It didn't take long and when aligned, the receiver worked very well.
After this initial experience, I spent much of my time building test equipment. During my involvement with test equipment, I developed the modern Vacuum Tube Volt Meter (VTVM), which for many years was the standard in the field. Mr. Hogan wasn't interested so I got my own patent (No. 2,039,267) which I assigned to a company who sat on it for several years. I, however, got the patent back and manufactured the VTVM during the war as one of three qualified suppliers of VTVMs by the War Production Board. I even sold a license to the U.S. Government.
Several devices were particularly associated with the high fidelity development program. (High fidelity can be defined as that fidelity which is a reproduction of live music that is so accurate that any practicable improvement is insignificant.) Working with Mr. Hogan, we drew up plans and specifications to submit to the FCC, with a request for a grant of a high fidelity broadcasting license. This could be the first of its kind and it would require something special, i.e. at least a 20 kHz channel. After some hearings and discussions, they granted us the 20 kHz channel at 1550 kHz. I went to work to provide genuine high fidelity broadcasting and reception. This involved analysis and solution of many problems not very important to those not dedicated to high fidelity.
An article in Electronics for Nov. 1935, pp. 26-29, describes some of the things I did in connection with the W2XR high fidelity project. Some components were available when I put together the W2XR's overall system-from studio microphone to listening room sound pressure-while others had to be created or improved. Starting with the source material, namely live studio or phonograph records, I spent considerable time analyzing and improving until we had high fidelity input. I regarded and still regard live studio programs the best source. Although, there has been substantial progress with "canned" music in the past few years.
In the early 30s, World Broadcasting had a good reputation for making records especially aimed at broadcasting programs. However, before we could play them to their best advantage, we had to improve available turntables. Typically turntables were heavy pedestal machines driven by a motor through a reducing gear. They rumbled badly when one extended the low frequency response down to my high fidelity criteria of 20 Hz. I took off the very heavy platter and interposed a soft sponge rubber pad between the drive shaft and the platter itself. This worked quite well.
Next I worked on the frequency response and distortion in the records. In playing them over, I felt that some sounded much cleaner than others. I made two high pass filters, one cutting off at 5000Hz and the other at 3500Hz. Now when I listened to only the high frequency components, the ones with greater distortion were very evident.
I graded the records A, B and C. The A records showed minimum distortion in the region above 5000 Hz; the B records showed distortion above 5000 Hz; and the C records showed distortion above 3500Hz. Then 1 made low-pass filters; a 3500 Hz cut-off filter for playing Crecords; a 5000 Hz filter for playing B records and no filter for playing A records. The filters were inserted with switching capabilities in the audio line of the W2XR transmitter. The operators were instructed to switch in the 3500 Hz filter for playing C records; the 5000Hz filter for B records and no filter for A records. When Mr. Hogan found out about this treatment of the prestigious World Broadcasting records he was very unhappy. He made me confront the World's management with my idea. They agreed I had a good idea since their records did have some problems.
It is interesting to note that back then records were generally made by engraving a wax master, gold sputtering and plating to form a die. The copies were pressed onto hot plastic of some kind. It was possible to make some very good records this way; although, there were some practical problems. Later on, and for many years, most mastering was done on magnetic tape where very low distortion is practically impossible. In other words, 1930 records could have better sound quality than later records.
I never accepted records as the best source of high fidelity. I told Mr. Hogan that if we were to claim high fidelity broadcasting, we must have some live programs. Reluctantly he agreed and I proceeded to design and build a studio at our Long Island facility.
I have already mentioned my equipment for measuring reverberation time. This W2XR studio was on the 11dead11 side but it was small and we had only a Baldwin piano for the sound source. We used Brush crystal microphones, the best at the time, and about the only High Fidelity microphone available (Proceedings of The Institute of Radio Engineers, May, 1934).
My experience with resistance coupled amplifiers at Browning-Drake and then with the 50 Hz response television signal amplifiers meant I had no trouble designing high fidelity preamps and main amplifiers. These were constructed by my able assistant, Russell Valentine. Also the modulation of the transmitter was straight-forward. The result was a very linear response and modulation from 20 Hz to 20 kHz and from zero • to one hundred percent modulation.
I devised a modulation monitor using a cathode ray tube. It not only responded instantaneously so that overmodulation was readily visible, but it also monitors the signal for any gross malfunction. No meter could do either function well. It was and still is the best possible monitoring device for audio or modulated wave signals. We never became involved with programs over the telephone lines. At one of our FCC hearings, one of their men objected to wired programs because his wife could hear something disturbing. I always felt the scientific basis for the objection should have been more than his wife's opinion.
While only indirectly concerned with high fidelity, we experimented with antennas and made signal strength measurements. In order to try a vertical antenna, I used a weather balloon to hold a vertical antenna wire. One warm day as we finished our experiments, the noon signal whistle was blown next-door. The balloon responded by bursting and letting down the antenna. To complete the picture, I built high fidelity receivers which were compatible with the W2XR wide-band output. One of the perennial limitations of radio reception is the loud speaker. Again the Brush crystal tweeter filled the gap and we had flat response to 20 kHz. (See the article on such a speaker in Proceedings of the Institute of Radio Engineers Vol. 21, No. 10, Oct. 1933, p. 1408.)
Thus, I feel that in the year 1934 I completed the first integrated high fidelity system ever put together in the world . Interestingly, approximately fifty years later, an engineer writing in a high technology magazine says, in spite of fancy claims and developments, the 20 Hz to 20 kHz is really all that is necessary for the faithful rendering of musical reproduction. I repeat I invented high fidelity at W2XR in 1934 and that distinction has never been eclipsed and never will be.