The photoelectric tone generator is one of the oldest and most popular designs for early electric musical instruments. The roots of this idea can be traced to 1890, when Ernest J.P. Mercadier used a rotating light interrupter with light-sensitive cells to create frequencies used for multiplex telegraphy. (This made it possible to send many messages simultaneously over a single wire.) Musical instruments using similar techniques began to appear during the early part of this Century. A modern photoelectric instrument is the Van Koevering (Vako) Orchestron, which reproduces sounds via endless-loop recordings that are inscribed in concentric circles on a single plastic tone disc. Theoretically, any sound that can be recorded might be used, including a variety of performed rhythm tracks.
A photoelectric tone generator has a light-sensitive cell that creates an electrical signal proportional to the amount of light that falls on it—the greater the light, the greater the signal. When this cell is subjected regularly to alternate periods of light and darkness, alternating current is generated. And as most people know, an alternating current in the audio frequency range will produce a sound when amplified and connected to a speaker.
Many types of photoelectric tone generators have been devised. One type has a rotating “tone wheel” that is placed between a light source and the photoelectric cell. Slits or other openings are cut radially on the wheel, and the wheel is rotated by a motor. The opaque sections that intervene between the slits interrupt, or modulate, the amount of light that passes from the lamp to the electric eye. The photoelectric cell “sees” alternate periods of light and dark. The pitch produced depends on the speed of rotation and the number of slits cut in the disc.
Ivan Eremeeff used such a design for an instrument constructed during the period 1933-35. The WCAU Photona was built in Philadelphia at the Electronic Music Studios of radio station WCAU. According to press reports, the Photona made its official debut in February, 1935, and was presented to the public over coast-to-coast and foreign broadcasts beginning in April, 1935.
The Photona was also known as the Eremeeff Organ. (There is no truth to the rumor that it was ever known as a “polyphonic ensemble.”) The Photona had twelve light choppers driven by a single endless belt connected to a synchronous electric motor. Slots were cut in such a way as to produce tones having various partials. Written accounts suggest that even the fundamental was a complex waveform, however. Associated with each light chopper was a photoelectric cell and seventy-five 6-volt automobile lamps—that’s a total of nine hundred lamps!
I am happy to report that, according to a timely magazine article, “…due to the short time duration of usage of each lamp, the percentage of burned-out lamps is so small as to be negligible.” And there is no truth to the rumor circulated by competitors that the instrument invariably caught fire when Henry Cowell’s keyboard clusters were performed!
Seriously, the lamps were connected, through different circuits, to the keyboard of two 73-note manuals and to “stops” which governed tone control. When a key on a manual was depressed, corresponding lamps were lit and the appropriate tone was “chopped” by the tone wheel. For timbre control, the partials of any tone could be varied in strength with knobs which increased or decreased the amount of current feeding into the appropriate lamps. (Technical trivia: Alternating current was used for keying these lamps; the Photona was constructed using no rectifiers.)
Eremeeff was a designer with an ear for musical nuance. In addition to the volume-control pedal that was standard fare for instruments of the era, he arranged for foot-operated control of vibrato amount. This was accomplished with a mechanical linkage that engaged a cam with a motor-driven gear; this in turn caused the displacement of the tone-generator drive belt on a cone-shaped pulley, creating true vibrato. This type of feature would be a welcome relief today from the constant-amount vibrato that still afflicts some electronic musical instruments.
The Photona also had a “percussion push” button that caused a sudden rush of current to the photoelectric cells, creating a cracking, percussive sound. Maybe Eremeeff was trying to provide a rudimentary dynamic keyboard for touch-responsive phrasing? Even though the Photona had an impossibly complex tone generator, there were sparks of genius in its musical engineering.
Of course, today we have electronic oscillators that can easily supplant electromechanical tone generators such as that of the Photona. So is there any real need for a photoelectric tone generator today? Yes and no. No, if we wish to produce only the classic rectangular, sawtooth, triangle, and sine waveforms—these can be generated easily and economically by an electronic oscillator. Yes, when exact replications of sounds such as the human voice and violins are desired; these are difficult to synthesize using electronic tone generators. Would the combination of the tone-shaping power of synthesizer modules with a photoelectric reader of acoustic sound be a felicitous marriage? In the next few columns we’ll explore older photoelectric instruments to give some idea of what has been and what might be.
JULY 1977
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