Oscillators

WR-921B

The WR-921B - a voice oscillator driven by a WR-921A driver, producing four simultaneous anti-aliased waveforms.

The WR-921B

The WR-921B is a voice voltage-controlled oscillator driven by a paired WR-921A. Pitch comes from a single CONTROL input at 1 V/Oct, typically fanned out from the WR-921A's FREQ OUT through a mult to several WR-921Bs at once. Four simultaneous ±5 V outputs (SIN, TRI, SAW, RECT) and a WDTH CV input for pulse-width modulation.

Two dedicated linear FM inputs sit alongside CONTROL. AC MOD is capacitor-coupled (DC drift blocked by an internal high-pass), useful for vibrato, AM, or audio-rate FM bells without permanent detuning. DC MOD is straight linear FM and preserves slow envelopes and offsets - drive it with an ADSR for pitch slides that don't drift back. Each input has its own front-panel attenuator (AC, DC).

A three-position SYNC selector phase-locks the oscillator on rising edges into the SYNC input. WEAK softly pulls phase toward zero on each edge - smooth beat-locking. OFF is independent operation. STRONG is hard sync - full phase reset, the classic lead synth ripping sound. A RANGE switch covers six octave-footage steps from LO (~5 octaves below 16') through 32' / 16' / 8' / 4' / 2', and the FINE knob provides ±12 semitones of fine tuning.

The WR-921B

The WR-921B has six controls: a FREQ fine-tune knob (±12 semitones), a RANGE switch in six octave-footage steps (LO drops ~5 octaves below 16'), a SYNC selector (WEAK / OFF / STRONG), a WIDTH knob (10% - 90%), and AC and DC linear-FM attenuators. Six inputs (CTRL, FINE, AC, DC, WDTH, SYNC) and four outputs (SIN, TRI, SAW, RECT) at ±5 V. Anti-aliasing uses polyBLEP on saw and rectangular outputs and an integrated triangle from polyBLEP square through a tanh-saturated DC blocker. STRONG sync does a full phase reset on each rising edge; WEAK sync blends 30% of the current phase toward zero for a smoother beat-locked wobble.

In a patch

The textbook WR-921B patch is the unison stack. Keyboard -> WR-921A F1 -> WR-921A FREQ OUT -> mult -> three or more WR-921Bs' CONTROL inputs. Each WR-921B's FINE knob is set a few cents off from the others. SAW outputs from all of them sum at a mixer and feed a WR-904A. The result is a thick, slightly-detuned super-saw lead.

The other classic WR-921B patch is linear FM. Run two WR-921Bs from the same driver. Patch one's SIN output into the other's DC MOD input, set the modulator's RANGE to a low setting and the carrier's RANGE high, and you have a basic FM operator pair. Integer ratios give bell-like tones, non-integer ratios give clangorous metallic textures.

For pad sounds, run several WR-921Bs from the same driver, each set to a different RANGE footage. 16' / 8' / 4' gives a three-octave stack that tracks the keyboard in parallel - press one note and you get the same chord every time. Send the mix through a WR-904A with a slow envelope and you have a string-machine sound.

Inputs

CTRL (cv) — Pitch CV from a WR-921A driver (1 V/oct). This is the primary pitch source - the WR-921B has no V/oct jack of its own.
FINE (cv) — Fine-tune CV, summed with the FREQ knob. Useful for pitch-bend from a ribbon or aftertouch source.
AC (cv) — AC MODULATE. Capacitor-coupled linear FM input (high-pass filtered around 5 Hz so slow DC drift is blocked). Good for audio-rate FM sidebands.
DC (cv) — DC MODULATE. Straight linear FM input. Use for LFO vibrato, envelope-driven pitch sweeps, or any slow modulation.
WDTH (cv) — Rectangular width CV. Typical source: WR-921A WDTH OUT for shared PWM, or an LFO for solo pulse-width motion.
SYNC (gate) — Phase-lock reference. Feed another oscillator's SAW or RECT output here. The three-position SYNC switch picks WEAK (soft phase nudge), OFF, or STRONG (hard sync reset).

Outputs

SIN (audio) — Sine output. Cleanest for FM carriers and sub bass. ±5 V Eurorack level.
TRI (audio) — Triangle output. Mellow and bass-heavy. Good for flutes and soft leads.
SAW (audio) — Sawtooth output. Harmonically rich - the classic subtractive-synth starting material.
RECT (audio) — Rectangular output. Width controlled by WDTH knob + WDTH CV. Square wave at 50 % duty, hollow at extremes.

Controls

Freq — FREQUENCY fine-tune. +/-12 semitones offset summed with the CONTROL input.
Range — RANGE switch. Organ-pipe octave footage: LO (below audio), 32', 16', 8', 4', 2'. Each step moves pitch one octave.
Sync — SYNCH. mode: WEAK (soft phase nudge toward 0 on rising edge), OFF (sync defeated), STRONG (hard sync reset).
Width — pulse width. 10-90% manual duty-cycle. Sum with WDTH CV input for PWM.

Synths.pw and the Classic-series modules are not affiliated with, endorsed by, or sponsored by Moog Music Inc. Module numbers reference the late-1960s American modular tradition and are used in a historical sense.

← Back to all modules