Doepfer A-121-3 Multi Filter
Four simultaneous filter outputs with voltage-controlled resonance
4 HP Eurorack module
The A-121 VCF 2 is a voltage-controlled multimode filter with a -12 dB/octave cut-off slope, simultaneously outputting low-pass, band-pass, high-pass, and notch (band-reject) signals. Built around the CEM 3320 filter IC, it offers voltage-controllable resonance up to self-oscillation, giving it a smooth, musical character suited to classic analog synthesis timbres, filter sweeps, and vocal-like formant effects.
Features
- Four simultaneous filter outputs: low-pass, band-pass, high-pass, notch
- -12 dB/octave cut-off slope
- Voltage-controlled cut-off frequency (two CV inputs: FCV 1 direct, FCV 2 with attenuator)
- Voltage-controlled resonance/Q (two CV inputs: QCV 1 direct, QCV 2 with attenuator)
- Resonance adjustable to self-oscillation for use as sine wave oscillator
- 1 V/octave tracking standard on FCV 1 and QCV 1
- Audio input level attenuator to manage distortion or add overdrive
- Built on CEM 3320 filter IC
- Resonance is largely frequency-independent below self-oscillation threshold
- Notch output produces phasing-like effect when f_c is LFO-modulated
Controls & Jacks (16)
- Audio Level — Input signal attenuator controlling the level of the audio signal entering the filter
- FCV 1 — Cut-off frequency CV input (1V/octave standard)
- Freq. — Cut-off frequency control for manual adjustment of the filter's center frequency
- Audio In — Audio input to the filter
- QCV 1 — Resonance CV input (1V/octave standard)
- FCV 2 — Secondary cut-off frequency CV input, level controlled by FCV 2 attenuator
- FCV 2 — Attenuator for the FCV 2 voltage control input, controlling the intensity of frequency modulation
- Q — Resonance (emphasis/Q) control, emphasizing frequencies around the cut-off point
- Band — Band-pass filter output
- Notch — Notch (band-reject) filter output
- High — output jack
- Low — Low-pass filter output
- FCV2 — Resonance (emphasis/Q) control, emphasizing frequencies around the cut-off point
- Res. — Resonance (emphasis/Q) control, emphasizing frequencies around the cut-off point
- HP — Secondary resonance CV input, level controlled by QCV 2 attenuator
- QCV 2 — Secondary resonance CV input, level controlled by QCV 2 attenuator
How-To Guides
- Classic Filter Sweep
- ADSR Envelope Filter
- LFO Wah Effect
- Self-Oscillating Sine Melody
- Notch Filter Phasing
- Spatial Spectrum Distribution
- Vocal Formant Synthesis
- Keyboard-Tracking Filter
- High-Pass Body Removal
- Voltage-Controlled Resonance Sweep
Explore the interactive A-121-3 Multi Filter panel on BleepDex — tap any control to learn what it does.
