Ultra-Simple Mono Audio Mixer

http://www.musicfromouterspace.com/

The simplest mixer ever. You can change the 39K feedback resistor to change the gain. Make the resistor value higher for higher gain or lower for less gain. The input gain pots can be anything from 10K to 1Meg, the value is not critical. Adjust the 100K feedback resistors in the headphone amp section to change the gain, again higher resistor values make the signal louder, lower resistor values make the signal softer. You could run this off of two nine volt batteries too.

Ultra-Simple Mono Audio Mixer Circuit Schematic