The modular system once developed by Robert "Bob" Moog, including its development process, went through a long production period between 1964 and 1981. At that time, the novel, electronic instrument was an avant-garde pioneering work that still had to be explained to the public; but ultimately found more and more interested parties. Behringer has transferred the generously dimensioned dimensions to the compact Eurorack format and paid close attention to ensuring that sound and function are in no way inferior to the cult object.

The Behringer 921A Oscillator Driver is capable of controlling the pitch of up to twelve connected 921B oscillators and adjusting the pulse width. The frequency range is switchable and adjustable in the range of +/- 6 octaves or +/- 12 semitones. Ideally this module is placed between keyboard or sequencer and at least one 921B oscillator. The lower knob sets the pulse width between 10% and 90%. For the pitch and the pulse width modulation there are two summed control voltage inputs each. If you don't want to modulate permanently with full intensity, you are advised to plan at least two attenuators for the Behringer 921A Oscillator Driver.