Doepfer - A-121-3 Multimode VCF Slim Line

The Doepfer A-121-3 Multimode VCF Slim Line is a compact yet powerful voltage-controlled filter offering four simultaneous outputs—lowpass, highpass, bandpass, and notch—all with a 12dB/oct slope. Designed to fit into smaller Eurorack systems without sacrificing flexibility, it provides both tonal versatility and responsive CV control.

Two frequency CV inputs allow for modulation via envelopes, LFOs, or sequencers. CV1 is calibrated for 1V/oct tracking, making it suitable for tuned filter work, while CV2 includes an attenuator for precise modulation depth. The resonance (Q) is manually adjustable and can also be voltage-controlled via its own CV input. At high settings, the A-121-3 will self-oscillate, turning it into a clean sine wave oscillator—ideal for experimental tones or melodic duties.

The input level control allows for soft saturation or more aggressive clipping when pushed, offering characterful distortion in a small package. Whether you're after subtle filtering or aggressive sweeps, the A-121-3 offers a lot of performance in just 4HP.

Key Features:

• Voltage-controlled multimode filter (12dB/oct)

• Simultaneous LP, HP, BP, and Notch outputs

• Self-oscillation for use as sine wave oscillator

• 1V/oct tracking on CV1 input

• CV-controlled resonance (CQ)

• Input level knob allows for clipping/distortion

• Compact 4HP Slim Line format

• Frequency range: approx. 10Hz – 20kHz