doepfer/a-127
A-127
Triple voltage-controlled resonant bandpass filter with three independent BP filter channels sharing a common audio input, each with internal triangle-wave LFO for frequency modulation, per-channel CV input, and individual audio outputs plus a summed mix output.436
Capabilities 5
- Bandpass Filterbandpass-filter
- 436
- LFOlfo
- Each of the three filter channels has its own internal triangle-wave LFO for frequency modulation, with independent rate and amplitude controls. When an external CV is patched, the LFO is switched out and the amplitude knob scales the external signal instead.436
- Multi-Channelmulti-channel
- 436
- Multiband Filtermultiband-filter
- A-127 has 3 independent parallel bandpass channels with per-channel CV control — a multiband filter by definition. Tagged manually 2026-05-17 because the extractor surfaced multi-channel only.
- Vcfvcf
- Three independent voltage-controlled bandpass filters sharing a common audio input; filter frequency is voltage-controllable per channel.436
Jacks 8 (4 in / 4 out)
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (4) | |||
| Audio In | audio | — | Common audio input shared by all three filters. Very sensitive; can be overdriven with normal A-100 signal levels.436 |
| Channel 1 ext. CV | cv | — | Filter frequency CV input for channel 1. When patched, the internal LFO is switched off; the CV Amplitude attenuator scales the external signal. One per channel (three total on module).436 |
| Channel 2 ext. CV | cv | — | 436 |
| Channel 3 ext. CV | cv | — | 436 |
| Outputs (4) | |||
| Channel 1 Audio Out | audio | — | Individual audio output for filter channel 1, carrying the signal processed by that filter. For modules made 1999 and later, not affected by the Audio Level control 7.436 |
| Channel 2 Audio Out | audio | — | 436 |
| Channel 3 Audio Out | audio | — | 436 |
| Mix Out | audio | — | Summed output from the internal mixer, combining the three filter outputs (each weighted by its Audio Level control) and the original signal (weighted by the Original control).436 |
Parameters 20
| Name | Type | Range | Behavior |
|---|---|---|---|
| Audio In Level | knob | — | Sets the level of audio signals coming into the Audio In input. The filter inputs are very sensitive; overdrive begins at about halfway on the attenuator's travel with a VCO input. Factory default: does not affect the Original signal level (controlled separately by the Original attenuator 8).436 |
| Channel 1 Audio Level | knob | — | Adjusts the contribution of channel 1's filter signal to the Mix output. For modules manufactured 1999 and later, does not affect the individual audio output. For earlier modules, affects both the individual output and the mix output.436 |
| Channel 1 CV Ampl. | knob | — | Adjusts the amplitude of the modulation signal for channel 1. When nothing is patched to the ext. CV jack, controls internal LFO amplitude. When an external CV is connected, scales that external voltage instead.436 |
| Channel 1 LFO Frq. | knob | 0.02Hz – 20Hz | Controls the frequency of the internal triangle-wave LFO for channel 1. LED indicator displays LFO activity.436 |
| Channel 1 LFO LED | menu_setting | — | LED gives a visual indication of the modulation signal produced by the LFO (or external CV) for channel 1.436 |
| Channel 1 Resonance | knob | — | Sets the filter resonance for channel 1. Higher values narrow the bandwidth of the bandpass response. Self-oscillation is not possible. In low-pass mode (via jumper), boosts frequencies around the filter cutoff point.436 |
| Channel 1 VCF Frq. | knob | 40Hz – 8000Hz | Sets the center frequency (fM) of the bandpass filter for channel 1.436 |
| Channel 2 Audio Level | knob | — | 436 |
| Channel 2 CV Ampl. | knob | — | 436 |
| Channel 2 LFO Frq. | knob | 0.02Hz – 20Hz | 436 |
| Channel 2 Resonance | knob | — | 436 |
| Channel 2 VCF Frq. | knob | 40Hz – 8000Hz | 436 |
| Channel 3 Audio Level | knob | — | 436 |
| Channel 3 CV Ampl. | knob | — | 436 |
| Channel 3 LFO Frq. | knob | 0.02Hz – 20Hz | 436 |
| Channel 3 Resonance | knob | — | 436 |
| Channel 3 VCF Frq. | knob | 40Hz – 8000Hz | 436 |
| Filter Type Jumper | jumper | — | Jumper on each filter circuit board selects bandpass (BP) or low-pass (LP) topology for that filter. Factory default is BP. Can optionally be wired to an external toggle switch for in-use switching.436 |
| Input Routing Jumper | jumper | — | Jumper on the mix circuit board controls whether the Audio In Level attenuator (1) also affects the Original signal. 'Pre' (factory default): attenuator 1 does not affect Original; 'Post': attenuator 1 controls both filter and Original levels together.436 |
| Original | knob | — | Sets the amount of the dry (unfiltered) original signal to be added to the mix output. Factory default: not affected by the Audio In Level attenuator 1, so the filtered and unfiltered signals can be controlled independently.436 |
Firmware history 0 versions
No firmware history recorded.
References 2
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[436]
Doepfer A-127 Triple Resonance Filter Manualmanual● verified 2026-05-17
- [437]