Moog 921 Oscillator (c. 1974)
The Moog 921 is the voltage-controlled oscillator module from the Moog modular systems of the mid-1970s. It came out around 1974 and was a more stable successor to the earlier 901/901b oscillators. The 921-series uses a master/slave setup. A 921A driver module sends common control voltages to one or more 921B slave oscillator modules. The 921B itself is a 2 MU-wide module.
Documentation on the hardware module is thin, but a few specifics survive. The oscillator generates periodic waveforms from .01 to 40,000 cycles per second, per the 1974 brochure. Power draw is listed as +12V @ 50mA and -6V @ 50mA - not ±15V. A July 1974 dated schematic exists in archive collections. The module has additional aux outputs and a clamp function. The 921 was also more stable than its 901 predecessors, with temperature compensation in the circuit. The Emerson Moog Modular System used standard 921B modules, built from original factory trace layout films.
Collectors say these are hard to find on the secondhand market. One forum user, comparing a clone against the original, remarked that the reproduction had "far far greater output than the original Moog 921." Another said the real thing is "NOT a reissue which is certainly not built the same (although Moog claims they have)."
Known specs:
- Voltage-controlled oscillator module (921B: 2 MU wide)
- Frequency range: .01 Hz to 40 kHz
- Power: +12V @ 50mA, -6V @ 50mA
- Waveforms: sine, triangle, sawtooth, pulse (simultaneously available)
- 921A driver / 921B slave architecture
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