Modulators

WR-902

A modular VCA - linear or exponential, three summing CVs, fixed control voltage knob.

The WR-902

The WR-902 is a voltage-controlled amplifier - the gain stage that turns a steady tone into a note by opening and closing under CV control. Three summing CV inputs and a FCV knob feed the gain element together; whatever they sum to drives the amp.

A LIN/EXP switch picks between two response curves. LIN runs gain linearly from 0 to x2 (+6 dB) as the control sum moves across 0-6 V, useful for CV mixing and audio-rate AM. EXP hits 0 dB exactly at 5.25 V and drops 12 dB/V below that, giving the natural analog-loudness feel and roughly 80 dB of dynamic range.

The signal section has a non-inverting input (IN+) and a differential subtract input (IN-), so the amplified signal is (IN+ minus IN-) before the gain stage. The output is exposed both in phase (OUT+) and inverted (OUT-) on complementary jacks, useful for phase-cancellation patches, balanced lines, or driving two destinations from one amp without needing a multiple. The whole signal path is DC-coupled, so the WR-902 sums envelopes and CVs as readily as it shapes audio.

The WR-902

The WR-902 has two main controls: a FCV knob (0-6 V scale, summed with all CV inputs) and a LIN/EXP mode switch. With the FCV knob at zero and nothing patched, the amp is silent; at 6 V it runs at unity gain. Three summing CV inputs (CV 1, CV 2, CV 3) at 1 V/oct add into the gain control. Signal section has a differential IN+ / IN- pair (the lower input is subtracted from the upper) and complementary OUT+ / OUT- outputs (one in phase, one inverted). DC-coupled across both signal and CV paths.

In a patch

The WR-902 sits at the end of an audio chain. The typical wiring is a WR-911 envelope into one of the three CV inputs with the FCV knob at zero - the envelope opens and closes the amp, shaping a steady oscillator into a note. Set the mode to EXP for natural musical loudness curves on audio, or LIN for ring-mod style tricks (push another oscillator into a CV input and the output is the product of the two signals).

Stacked CV inputs are the WR-902's strength. Patch a WR-911 envelope into CV 1 for amplitude shaping, an LFO into CV 2 for tremolo on top, and a slow accent envelope into CV 3 for dynamics - all three sum into the same gain stage. Because the module is DC-coupled, with no audio patched it doubles as a CV summer for combining envelopes or mixing pitch CVs. The complementary OUT+ / OUT- outputs feed two destinations from one amp without needing a separate mult.

Inputs

IN (audio) — Signal input. Any audio or CV can flow through the amp. Since the WR-902 is DC-coupled, you can use it as a CV attenuator as well as an audio VCA.
CV 1 (cv) — Control input 1 - summed with CV 2, CV 3, and FCV. Typical routing: WR-911 envelope output for note-shaped amplitude.
CV 2 (cv) — Control input 2 - summed with the others. Good for a tremolo LFO on top of an envelope patched to CV 1.
CV 3 (cv) — Control input 3 - summed with the others. Useful for a secondary accent or dynamics envelope layered over the primary envelope.

Outputs

OUT (audio) — Signal output. Audio multiplied by the CV-plus-FCV-derived gain. Feeds directly into the patch graph with low source impedance.

Controls

FCV — Fixed Control Voltage. 0-6 V manual offset summed with the CV inputs. At 0 V the WR-902 is silent (LIN) or near silent (EXP); at full clockwise you get up to 2x linear gain.
Mode — Response mode. LIN = linear: output scales proportionally with the CV sum, great for CV processing and ring-mod. EXP = exponential: roughly unity at the middle of the CV sum and -12 dB per volt below. Use EXP for natural amplitude envelopes on audio so quiet parts feel quiet and loud parts hit hard.

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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