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:How to build Stereo to Mono Converter Based on FET - circuit diagramParts:
  • 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
  • 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.

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