This 2 channels audio mixer is based on the 2n3904 transistors which forms 2 pre-amplifiers. The first preamplifier of the audio mixer has a high gain and can be used for microphone input, and the ...

Here is a multi channel audio mixer circuit based on 2N3819 n-channel JFET. It mixes as many as inputs into one channel. The design seen in the diagram is for only two channels (stereo into mono) but ...