Oscillators

WR-921

The WR-921 - a standalone voice oscillator with four simultaneous waveforms, switchable AUX, and a CLAMPING phase-reset trigger.

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The WR-921

The WR-921 is a standalone voltage-controlled oscillator with 1 V/Oct pitch tracking, three summing frequency CV inputs, two summing pulse-width CV inputs, four simultaneous waveform outputs (SIN, TRI, SAW, RECT), a sixth AUX output whose waveform is selected by a rotary switch, and a phase-resetting CLAMPING trigger input.

Two pitch controls shape the FREQUENCY knob's behaviour. The SCALE switch picks the knob span: SEMI covers ±12 semitones for fine intervalic tuning, OCT covers ±6 octaves for coarse transpose. The RANGE rotary is an octave footage selector marked LO / 32' / 16' / 8' / 4' / 2' / 1' that snaps pitch in octave steps. A separate SUB-AUDIO switch divides the frequency by 100 for true LFO rates.

The CLAMPING input is the WR-921's distinctive feature. A V-trig rising edge instantly resets the waveform's phase to a user-set point on the cycle (the clamping point knob), locking the oscillator to a clock. Useful for pitched kick drums, phase-coherent unison, or beat-locked sub-tones. The AUX output picks from SIN / TRI / SAW / -SAW / RECT / -RECT via a rotary selector and has its own LEVEL knob (0-5x gain) that can deliberately overdrive the next module.

The WR-921

The WR-921 has eight controls: a FREQ knob, a SCALE switch (SEMI / OCT), a RANGE switch (SUB-AUDIO / AUDIO, where SUB-AUDIO divides frequency by 100 for LFO use), an octave-footage OCT rotary (LO / 32' / 16' / 8' / 4' / 2' / 1'), a WIDTH knob (10% - 90%), an AUX waveform selector, an AUX level knob (0-5x gain), and a CLAMP knob setting the phase-reset point. Six inputs (F1, F2, F3, W1, W2, CLMP) and six outputs (SIN, TRI, SAW, RECT, AUX+, AUX-). Fixed waveform outputs are ±5 V; AUX can hit ±25 V at full level. Anti-aliasing uses polyBLEP on saw and rectangular outputs and an integrated triangle from polyBLEP square through a tanh-saturated DC blocker. CLAMP triggers ramp the output back from 0 to 1 over ~1 ms after each phase reset for clean settling.

In a patch

In a typical voice patch the WR-921 sits at the head of the chain. Keyboard or sequencer -> WR-921 V/Oct input -> SAW output into a WR-904A low-pass filter -> WR-902 VCA -> output. A WR-911 ADSR triggered by the same gate sweeps the WR-904A cutoff and shapes the WR-902's amplitude.

The CLAMP input opens patches the WR-921B cannot do. Patch a clock into CLMP and the SIN output becomes a phase-coherent kick drum - every cycle starts at the same point. Patch a fast decay envelope into F1 at the same time and you get the characteristic downward pitch sweep of an analog kick. For unison patches, run several WR-921s with the same V/Oct on F1 and the same clock on CLMP, then detune them with the FREQUENCY knob - the result is a thick, rhythmically-locked super-saw voice.

The AUX output is for dual-purpose patches. Send the main SAW into the filter chain and route AUX (set to inverted RECT) into a noise gate or sidechain - the inverted pulse becomes a rhythmic ducking signal. Or stack two WR-921s with one feeding its AUX into the other's width-1 input for cross-modulated PWM textures.

Inputs

F1 (cv) — Frequency CV input 1 (1 V/oct). Primary pitch input.
F2 (cv) — Frequency CV input 2. LFO vibrato or second CV source here.
F3 (cv) — Frequency CV input 3. Envelope for pitch sweeps, or sequencer for melody.
W1 (cv) — Rectangular width CV 1. LFO here gives PWM on the RECT output.
W2 (cv) — Width CV 2. Layer with W1 for complex PWM motion.
CLMP (gate) — clamp trigger. V-trig rising edge resets the waveform phase to the clamping point setting - makes the oscillator rhythmically lockable.

Outputs

SIN (audio) — Fixed-level sine. ±5 V Eurorack.
TRI (audio) — Fixed-level triangle. Mellow tone.
SAW (audio) — Fixed-level sawtooth. Rich harmonic content for subtractive filtering.
RECT (audio) — Fixed-level rectangular. Width controlled by knob + CV.
AUX (audio) — Auxiliary output with switch-selectable waveform (SIN / TRI / SAW / -SAW / RECT / -RECT) and independent level knob.

Controls

Freq — FREQUENCY. Manual pitch offset. Scale selected by the SCALE switch.
Scale — SCALE switch. SEMI = +/-12 st (2 octaves), OCT = +/-6 oct (12 octaves).
Range — COARSE RANGE switch. SUB-AUDIO drops frequency by 100x (LFO / drone); AUDIO is normal oscillator range.
Oct — RANGE switch. Organ-pipe octave footage: LO, 32', 16', 8', 4', 2'. Each step moves pitch one octave.
Width — pulse width. 10-90% pulse width for the RECT output.
AuxWv — AUX OUT WAVEFORM. Selects one of six: SIN / TRI / SAW / -SAW (inverted) / RECT / -RECT (inverted).
AuxLv — AUX OUT LEVEL. Independent level for the AUX output, 0 to 7 V p-p for sine/tri/saw waveforms.
Clamp — clamping point. 0-100% of the cycle - the phase to jump to on CLMP rising edge.

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.

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