doepfer/a-103
A-103 18dB Low Pass Filter (TB-303)
Voltage controlled 18dB/octave lowpass filter based on a modified transistor ladder (Moog ladder), reproducing the legendary TB-303 filter circuit. Features three CV inputs, manual cutoff frequency and resonance controls up to self-oscillation.321
Visualization filter_response
Capabilities 2
- Self-Oscillationself-oscillation
- Cascaded 18 dB/oct ladder (TB-303 lineage); at maximum resonance the filter self-oscillates and tracks 1V/oct.321
- Vcfvcf
- 18dB/octave lowpass filter based on modified TB-303 transistor ladder. Three CV inputs with 1V/oct tracking on CV1; resonance adjustable to self-oscillation.321
Jacks 5 (4 in / 1 out)
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (4) | |||
| Audio In | audio | — | 321 |
| CV 1 | cv | — | Standard CV input for filter cutoff frequency, follows 1V/octave standard. Can be used for LFO/ADSR modulation, pitch tracking, or as pitch CV when using the filter as a sine wave oscillator.321 |
| CV 2 | cv | — | Additional CV input for filter cutoff modulation, with attenuator to control modulation intensity.321 |
| CV 3 | cv | — | Additional CV input for filter cutoff modulation, with attenuator to control modulation intensity.321 |
| Outputs (1) | |||
| Audio Out | audio | — | Filter output, sends out the filtered signal.321 |
Parameters 5
| Name | Type | Range | Behavior |
|---|---|---|---|
| CV 2 Attenuator | knob | — | Attenuates the CV 2 input signal to control modulation intensity on the filter cutoff.321 |
| CV 3 Attenuator | knob | — | Attenuates the CV 3 input signal to control modulation intensity on the filter cutoff.321 |
| Frq | knob | 0 – 10 | Adjusts the filter cutoff frequency. At maximum (10) the filter is fully open; turning down progressively attenuates higher frequencies; at 0 the filter is completely shut with no output.321 |
| Lev. | knob | — | Controls the level of the audio input signal going into the filter. If the filter output distorts, turn this control down unless distortion is desired.321 |
| Res. | knob | — | Sets the filter resonance (emphasis/Q), emphasising frequencies around the cutoff point. Near maximum, the filter self-oscillates and behaves like a sine wave oscillator.321 |
Firmware history 0 versions
No firmware history recorded.
References 2
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[321]
Doepfer A-103 18dB Low Pass Filter manual (English)manual● verified 2026-05-14
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[322]
Doepfer A-103 18dB Low Pass Filter (TB-303) product pageproduct_page● verified 2026-05-14