Rongge

This circuit is used for controlling the volume of output  and then entered the mixer, but this circuit not only as the volume setting. This circuit also serves to reduce noise , and increase the gain  at the signal coming from the output. See schematic , PCB line ,and construction below   Master mixer circuit Looked Down Looked Up

General Description: Above schematic is for a three channel audio mixer. That will provide an overall gain of one between the output and each input channel. Each input channel includes a single 0.1uf capacitor and 100-Kilohms resistor to provide an output impedance of 100K. The number of input channels to this audio mixer can be increased by adding more capacitors and resistors with same value as capacitor(0.1uf) and resistor(100K). The mixer should be located between the output of tone control circuitry and the input to the power amplifier. One input should be taken from the output of the tone control circuit, and the other inputs should either be grounded or taken from desired source. Circuit diagram: Three Channel Audio Mixer circuit diagram

This audio mixer circuit doesn’t use a low impedance input to mix no ideal  sources, but use many amplifiers to provide  ideal sources before mixed through simple resistors. Ideal source means a sources with low impedances, make the interaction between signals in the output doesn’t affect the input.   Please note that this mixer circuit has high impedance output, so you’ll need an next processing equipment with appropriate  input specs. This audio mixer circuit is designed around an LM3900 quad op amp and combines 2 line and 2 mike inputs and sums them at the output terminal. To vary the gain (around +23 dB), we can change the R7 through R10.  LM3900 Audio Mixer Circuit Diagram