doepfer/a-108
A-108 6/12/24/48dB Low Pass Filter
Voltage-controlled transistor-ladder (Moog ladder) lowpass filter with 8 internal filter stages (6–48 dB/oct). Four simultaneous lowpass outputs at 6, 12, 24, and 48 dB/oct (factory default), plus a band pass output. Three CV inputs for frequency control; external feedback input for voltage-controlled resonance.319
Visualization filter_response
Capabilities 5
- Bandpass Filterbandpass-filter
- Band pass output derived from the transistor ladder, available simultaneously with the lowpass outputs.319
- Lowpass Filterlowpass-filter
- Transistor ladder (Moog) lowpass filter with four simultaneous outputs at 6, 12, 24, and 48 dB/oct slopes (factory). Self-oscillates at maximum resonance.319
- Self-Oscillationself-oscillation
- Moog-style transistor ladder; at maximum resonance the filter self-oscillates and can track pitch.319
- Sine Wave Oscillator (self-oscillation)sine-oscillator
- At maximum resonance the filter self-oscillates as a sine wave oscillator; pitch tracks via CV1 (approx. 1V/oct). Self-oscillation breaks off at high audio input distortion.319
- Vcfvcf
- Voltage-controlled multi-tap Moog ladder filter.319
Jacks 10 (5 in / 5 out)
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (5) | |||
| Audio In | audio | — | Audio input to the filter. Very sensitive — distortion is possible even with normal A-100 levels.319 |
| CV1 | cv | — | CV input for filter frequency control, approximately 1V/octave. No attenuator.319 |
| CV2 | cv | — | CV input for filter frequency control with attenuator. At fully clockwise sensitivity is about 0.5V/octave.319 |
| CV3 | cv | — | CV input for filter frequency control with attenuator. At fully clockwise sensitivity is about 0.5V/octave.319 |
| Feedb. | audio | — | External feedback input for resonance path. Normalled to the 48 dB LP output. Allows insertion of external modules (e.g. VCA for voltage-controlled resonance) into the feedback loop.319 |
| Outputs (5) | |||
| 12dB LP | audio | — | Lowpass output at 12 dB/octave slope (factory default assignment for output 2; jumper-configurable to 18 dB).319 |
| 24dB LP | audio | — | Lowpass output at 24 dB/octave slope (factory default assignment for output 3; jumper-configurable to 30 or 36 dB).319 |
| 48dB LP | audio | — | Lowpass output at 48 dB/octave slope (factory default assignment for output 4; jumper-configurable to 42 dB). Also the normalled source for the feedback input.319 |
| 6dB LP | audio | — | Lowpass output at 6 dB/octave slope (factory default assignment for output 1).319 |
| BP | audio | — | Band pass output using the transistor ladder topology.319 |
Parameters 5
| Name | Type | Range | Behavior |
|---|---|---|---|
| Audio Level | knob | — | Attenuates the audio input signal level entering the filter. If the output distorts, turn this control down. Distortion appears from about position 5 with normal A-100 audio levels.319 |
| CV 2 | knob | — | Attenuator for CV2 input signal level controlling filter frequency. At fully clockwise (position 10), sensitivity is about 0.5V/octave.319 |
| CV 3 | knob | — | Attenuator for CV3 input signal level controlling filter frequency. At fully clockwise (position 10), sensitivity is about 0.5V/octave.319 |
| Emph. | knob | — | Controls the filter's resonance (emphasis/Q). Emphasises frequencies around the cutoff point. For the band pass, changes bandwidth. At maximum, filter self-oscillates as a sine wave oscillator. Self-oscillation breaks off at high distortion levels.319 |
| Freq. | knob | — | Manually adjusts the filter cutoff frequency (lowpass) or middle frequency (band pass). The actual filter frequency is the sum of this control and the external CV inputs CV1–CV3.319 |
Firmware history 0 versions
No firmware history recorded.
References 2
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[319]
Doepfer A-108 6/12/24/48dB Low Pass Filter manual (English)manual● verified 2026-05-14
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[320]
Doepfer A-108 6/12/24/48dB Low Pass Filter product pageproduct_page● verified 2026-05-14