The module Doepfer A-138b Logarithmic Mixer is a four channel mixer, which can be used with either control voltages or audio signals. Each of the four inputs has an attenuator, and there’s a master attenuator, so that the mixer can be used at the end of the audio chain – ie. it can be used to interface directly with an external mixer, amplifier, etc.

The module can be supplied in two versions:
Doepfer A-138a Linear Mixer: potentiometers with linear response, so especially suitable for control voltage mixing.
Doepfer A-138b Logarithmic Mixer: potentiometers with logarithmic response, so especially suitable for audio signal mixing.

Note: Since April 2004 improved versions of the modules are manufactured. For the revised versions control In1 works as a DC offset generator (about 0…+5V) provided that no patch cord is plugged into socket In1. If this feature is not required it can be deactivated by removing a jumper on the pc board.

Doepfer A-138b Logarithmic Mixer Specifications:
– Width: 8HP / 40.3 mm
– Depth: 35 mm (measured from the rear side of the front panel)
– Current: +10mA (+12V) / -10mA (-12V)