921a driver

moog921a · modulation · schema v1

921A Oscillator Driver (moogafakkin System 55/35 clone — categorized under Ports -> moogafakkin). A CONTROL-VOLTAGE PROCESSOR, NOT a sound source: it generates the two control voltages on a bus that drive N slaved 921B oscillators — a frequency CV (freq_bus, V/oct, encoding pitch) and a pulse-width CV (width_bus, 0..1). The FREQUENCY pot is mapped onto V/oct by a two-position frequency-RANGE switch — SEMITONE (a tight 2-octave fine compass) or OCTAVE (a wide 12-octave coarse compass). Summing FREQ + WIDTH CONTROL INPUTS add onto the buses per-sample (freq_cv is a V/oct pitch cable that sums 1:1 onto freq_bus; width_cv sums onto width_bus). NO audio inputs and NO audio outputs — the outputs are CV cables that feed a 921B's freq_bus / width_bus. DSP is own-code: pure CV math (exponential frequency mapping + width passthrough), not a port of any moogafakkin schematic or copyleft source - permissive only. Beige moogafakkin faceplate (the intrinsic always-on look shared by the moogafakkin module family). Ships together with the 921B (the 921A is meaningless without a slaved 921B).

A clean-room recreation of the Moog 921A Oscillator Driver — the master half of the System 55/35 two-part oscillator. It is NOT a sound source: it makes no audio of its own. Instead it generates the two CONTROL VOLTAGES — a 1V/oct pitch bus and a pulse-width bus — that drive one or more slaved 921B oscillators, so a whole bank of 921Bs tracks one set of FREQUENCY/RANGE/WIDTH knobs (and one pitch CV) in perfect unison. Mental model: it is the pitch+width 'brain' you patch into every 921B's FREQ BUS and WIDTH BUS so they play together; tune here, hear it on the 921Bs.

the faceplate

2 inputs · 2 outputs · 3 params

inputs

id	cable	what it does
`freq_cv`	pitch	1V/oct pitch CV summed onto the FREQ knob (and the RANGE compass) per sample, then sent out on the freq bus — patch a keyboard or sequencer here to play every slaved 921B at once. V/oct pitch CV; modulates frequency (summed directly (the destination DSP scales it))
`width_cv`	cv	Pulse-width CV summed onto the WIDTH knob per sample and passed through to the width bus, so an LFO here animates the pulse width of every 921B driven by this module simultaneously (ganged PWM). control voltage (CV); modulates width (summed directly (the destination DSP scales it))

outputs

id	cable	what it does
`freq_bus`	cv	The 1V/oct frequency control voltage. Patch it into each 921B's FREQ BUS input so they all follow this module's pitch (knob + freq_cv). control voltage (CV)
`width_bus`	cv	The 0..1 pulse-width control voltage. Patch it into each 921B's WIDTH BUS input so their rectangular outputs share one width (knob + width_cv). control voltage (CV)

params

id	label	range	default	curve
`frequency`	Freq	-1..1	0	linear
`freqRange`	Range	1..2	1	discrete
`width`	Width	0..1	0.5	linear

controls

control	what it does
Range	RANGE switch: 1 = SEMITONE (the FREQUENCY pot spans a narrow ~2-octave window for fine tuning) / 2 = OCTAVE (the pot spans a wide ~12-octave compass for big sweeps).
Freq	The FREQUENCY pot, a normalized -1..1 that the RANGE switch maps onto the pitch bus — the coarse tuning for every 921B this driver feeds.
Width	Pulse width sent on the width bus, 0 to 1 (0.5 = a 50% square), driving the rectangular output of every 921B that reads this bus.

source

moog921a.ts on GitHub.