Single transistor audio mixer. Many audio mixer circuits have
been published here. But I think, this one is the simplest of
them. This very simple audio mixer circuit uses only one
transistor. The base emitter junction of the transistor is
biased by the diodes D1 and D2.The signals to be mixed are
directly coupled to the base of Q1.Each input lines are current
limited by using a 33K resistor. With the used component values
the collector current is around 1mA. Circuit diagram with Parts
list. - The circuit can be assembled on a Vero board. - The
circuit can be powered from 15V DC. - Gain of the individual
channels can be adjusted by adding a 10K POT in series to the
lines.