Doepfer — A-135-1
Doepfer A-135 VC-Mixer Manual (PDF)
Doepfer A-135 VC-Mixer (System A-100) Cheat Sheet
The Doepfer A-135 VC-Mixer is a 4-channel voltage-controlled mixer combining four linear VCAs and a mixer. It allows voltage-controlled mixing of up to 4 audio signals with individual CV or manual control, suited for both audio and some CV duties.
Inputs & Outputs (Sockets)
| Label |
Type |
Function |
Voltage Range |
Audio In 1-4 (!) |
Input (x4) |
Audio inputs for each VCA channel |
Audio levels (typ. ~10Vpp) |
Audio Out (") |
Output |
Sum output of all 4 VCAs mixed |
Audio levels (~10Vpp) |
ext. CV 1-4 (§) |
Input (x4) |
CV input for each VCA |
0V (off) to +5V (max gain) |
Controls
| Control |
Per VCA? |
Description |
| Audio In |
Yes |
Attenuates the signal at the corresponding Audio In. |
| Gain |
Yes |
Sets manual gain/offset for the channel. 0 = off, increasing gives more base gain. |
| ext. CV |
Yes |
Attenuates the amount of external control voltage affecting the VCA. |
- Audio In (1-4): Use the knob to set initial signal level for each audio input.
- Gain (1-4): Sets minimum VCA level (offset). Typically set to 0 for unipolar sources (like envelopes); increase for bipolar CV sources (like LFOs) to allow negative swings to have effect.
- ext. CV (1-4): Attenuates the external CV input; sets how much modulation affects the VCA.
Reference Notes
- All VCAs are linear response.
- Typical use: Patch sources (VCOs, samplers, external signals, etc.) into Audio In 1-4. Output to sound system or further processing.
- CV modulates amplitude: e.g. use envelopes for dynamics or LFOs/random for movement.
- 0V CV = VCA muted; +5V CV = VCA at max gain. Control sources include envelopes, LFOs, sequencers, random, etc. (see manual for examples).
Patch Example
- Plug up to 4 audio sources into Audio In jacks.
- Optionally patch a control voltage (envelope, LFO, etc.) into ext. CV for one or more channels.
- Set Audio In and Gain knobs for basic level.
- Use ext. CV knob to set CV modulation depth.
- Main output is at Audio Out.
Module Panel Summary
- Inputs:
Audio In 1-4 (signal), ext. CV 1-4 (0-5V, controls VCA)
- Output:
Audio Out (summed/mixed VCA outputs)
- Knobs per channel:
Audio In (attenuator), Gain (offset), ext. CV (CV attenuator)
- No buttons, switches, or sliders.
Additional References
- CEM3381 VCA chips, high quality, linear response.
- Voltage range: For full VCA opening, ext. CV input expects up to +5V (in addition to offset from Gain knob).
For detailed patch diagrams, refer to the Patch-Sheet section in the full manual (PDF).
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