Doepfer — A-121-3

Manual PDF

Doepfer A-121-3 12dB Multimode Filter Slim Line Series Manual

Doepfer A-121-3 Cheat Sheet

Type: Voltage-controlled multi-mode filter
HP: 4
Depth: 50mm
Current Draw: +40mA (+12V) / -30mA (-12V)
Price: ~€110
Cutoff Slope: -12dB/octave
Freq. Range: ~10Hz–20kHz
Features: Simultaneous LP, HP, BP, Notch outputs

Inputs, Outputs, & Controls

Inputs

Jack	Function	Voltage Range / Notes
In	Audio signal input	Adjustable with Level knob
CV1	Filter cutoff control (1V/Oct)	~0–8V, no attenuator
CV2	Filter cutoff modulation	~0–8V, has dedicated attenuator (FCV2)
CQ	Resonance (Q) control voltage	0–8V, no attenuator

Outputs

Jack	Output Type	Notes
LP	Low-pass filtered output
HP	High-pass filtered output
BP	Band-pass filtered output
N	Notch/Bandsperre filtered output

Knobs / Controls

Label	Function	Notes
Frequ.	Manual cutoff frequency	Sweeps filter freq. from 10Hz–20kHz
Q	Resonance (manual)	Full CW will self-oscillate (sine out)
FCV2	CV2 attenuator (modulation depth)	Ranges from 0 to full incoming voltage
Level	Audio input gain/attenuator	Start seeing distortion/clipping >5

Quick Reference

Use In for your audio source & adjust Level for input gain (beware distortion beyond position 5).
Frequ. sets the base cutoff frequency; CV1 (1V/oct) and CV2 (variable depth via FCV2) control cutoff via CV.
Patch an envelope, sequencer, or LFO to CV1/CV2 for animation.
Patch a CV source to CQ for voltage control over resonance (no attenuator here).
Q knob manually sets resonance—self-oscillation possible when fully clockwise.
Simultaneous outputs: LP (Low-pass), HP (High-pass), BP (Band-pass), N (Notch).
Perfect for compact cases (4HP), similar in sound/function to A-121-2 but smaller (no CQ attenuator).

Voltage Ranges

Cutoff frequency CVs (CV1, CV2): expect standard modular levels (usually 0–8V), 1V/Oct on CV1.
Resonance CV (CQ): 0–8V recommended.
Output audio: Standard modular levels (typically ±5V peak-to-peak).
Input audio: Standard modular levels (adjust with Level).