doepfer-a-138o

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.

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