doepfer/a-121-3
A-121-3 12dB Multimode Filter (Slim Line)
Slim line 4HP voltage-controlled multimode filter with -12 dB/octave slope, four simultaneous outputs (LP, HP, BP, Notch), voltage-controlled resonance, and self-oscillation capability.325
Visualization filter_response
Capabilities 2
- Multimode Filtermultimode-filter
- 12 dB/octave multimode VCF with simultaneous LP, HP, BP, and Notch outputs. Self-oscillates as a sine oscillator. CV control over both cutoff and resonance.325
- Self-Oscillationself-oscillation
- Filter self-oscillates at high resonance settings, functioning as a sine wave oscillator without any audio input.325
Jacks 8 — 4 in / 4 out
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (4) | |||
| CQ | cv | — | CV input for resonance (Q) control without attenuator.325 |
| CV1 | cv | — | CV input for filter cutoff frequency without attenuator, approximately 1V/octave sensitivity.325 |
| CV2 | cv | — | CV input for filter cutoff frequency with paired attenuator FCV2 for modulation depth control.325 |
| In | audio | — | 325 |
| Outputs (4) | |||
| BP | audio | — | Band-pass filter output, -12 dB/octave slope.325 |
| HP | audio | — | High-pass filter output, -12 dB/octave slope.325 |
| LP | audio | — | Low-pass filter output, -12 dB/octave slope.325 |
| N | audio | — | Notch (band-reject) filter output, -12 dB/octave slope.325 |
Parameters 4
| Name | Type | Range | Behavior |
|---|---|---|---|
| FCV2 | knob | — | Attenuator for the CV2 frequency modulation input. Sets the modulation depth of the CV2 input signal.325 |
| Frequ. | knob | 10Hz – 20000Hz | Sets the filter cut-off frequency manually. The frequency range spans approximately 10Hz to 20kHz.325 |
| Level | knob | — | Attenuator for the audio input In. Beyond approximately position 5, clipping/distortion occurs with typical A-100 audio levels.325 |
| Q | knob | — | Sets filter resonance manually. Resonance can be increased up to self-oscillation, at which point the filter acts as a sine wave oscillator even without an audio input signal.325 |
Firmware history 0 versions
No firmware history recorded.
References 1
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Doepfer A-121-3 12dB Multimode Filter (Slim Line) product pageproduct_page● verified 2026-05-14