This 2 channels audio mixer is based on the 2n3904 transistors which forms 2 preamplifiers. The first preamplifier of the audio mixer has a high gain and can be used for microphone input, and the second one can be used to control the input of the audio level. This two channel audio mixer require a power supply with the output voltage between 9 to
12 volts. For the audio signal you can use a CD player, mp3 player or other audio device and for the microphone you can use a normal dynamic microphone.