Doepfer A-138o Octave Controller
Four-channel mixer for audio and control voltages
4 HP Eurorack module
The A-138 Mixer is a four-channel audio and control voltage mixer for the Doepfer A-100 modular system. It features individual attenuators for each of its four inputs plus a master output attenuator, making it equally suited for blending audio signals or combining multiple control voltages into a single composite CV. Its two versions — linear (A-138a) and logarithmic (A-138b) — tailor the response curve to CV or audio duties respectively.
Features
- Four independent audio or CV inputs each with dedicated attenuator
- Master output attenuator for direct interfacing with mixers and amplifiers
- Available in linear (A-138a) and logarithmic (A-138b) potentiometer versions
- Usable for both audio signals and control voltages
- Optional DC offset function for Input 1 via internal JP4 jumper (mid-2004 onward)
- Positive offset (~0 to +5V) or negative offset (~0 to -5V) selectable via JP4 jumper position
- Offset active only when no plug inserted into Input 1 socket
Controls & Jacks (7)
- Main Level — Master output level control for the stereo mix sent to the Left and Right outputs
- Aux Send — Controls the level of the signal sent to the Aux Send Output jack for external effects processing
- Aux Return — Controls the level of the signal returning from external effects via the Aux Return Input jack
- Aux Send Output — Sends signal to an external effects processor at the level set by the Aux Send knob
- Aux Return Input — Receives the processed signal back from an external effects processor
- Left Output — Left channel stereo output at the level set by Main Level
- Right Output — Right channel stereo output at the level set by Main Level
How-To Guides
- Blending Two VCO Waveforms
- Multi-Source CV Modulation for VCF
- Four-Oscillator Drone Pad
- Positive DC Offset as Bias Voltage
- Layered Envelope Routing for Percussion
- Modular Submix to External Mixer
- Morphing LFO Depth via CV Attenuation
- Negative Offset for Downward Transposition
Explore the interactive A-138o Octave Controller panel on BleepDex — tap any control to learn what it does.
