Stereo to Mono Converter Based on FET

High quality portable unit, Suitable for Sub-woofer amplifiers

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

Circuit Diagram:

Large View

Parts:

P1 = 10K-50K Pot
P2 = 10K-50K Pot
R1 = 100K
R2 = 100K
R3 = 6.8K
C1 = 0.1uF-25V
C2 = 0.1uF-25V
C3 = 0.1uF-25V
Q1 = 2N3819 Junction FET
J1 = Audio input sockets
J2 = Audio input sockets

Notes:

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 clearly shown on the schematic.
One version of this mixer I saw had 18 inputs!
A shielded case is probably needed to reduce hum and help stop oscillations.
P1 and P2 are dual gang potentiometer for stereo version.
The circuit can be powered by a single 9 volt battery.

Source : www.uashem.com