SINGLE TRANSISTOR AUDIO MIXER

1. This very simple audio mixer circuit uses only one transistor.
2. The base emitter junction of the transistor is biased by the diodes D1 and D2.
3.  The signals to be mixed are directly coupled to the base of Q1.
4. Each input lines are current limited by using a 33K resistor. With the used component values the collector current is around 1mA.
    
    
    
    
   NOTES:
   

   • 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.