FET Audio Mixer

This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic.

Parts
R1,R3            2               10k pot
R2,R4            2               100k
R5                 1               6.8k
C!,C2,C3        3              0.1uF capacitor
Q1                1               2N3819 junction fet
MISC            1               wire,shielded(metal)case,phono or other plug for ouput


Notes

1. As many or as few channels as are required can be added to the mixer. Do this by just duplicating the input "sections" which are shown on the schematic.
2. A shielded case is probably needed to reduce hum and help stop oscillations.
3. The circuit can be powered by a single 9 volt battery.

source