Ray Wilson authored this content while he was actively running MFOS as the founder and resident genius.
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Article by Ray Wilson

Simple Audio Mixer

You can add more inputs to this circuit. The gain is set to x1 in this schematic. You can change the gain by adjusting the resistor values. By lowering the value of an input resistor you increase the gain for that input. By raising the value of an input resistor you decrease the gain for that input. The gain formula is feedback resistor divided by input resistor. The 47pF is to stop high frequency oscillation of the OP-Amp (you might not need it).