6-channel audio mixer

6-channel audio mixer

The mixer circuit below has 3 line inputs and 3 microphone inputs. The microphone inputs are suitable for low-impedance dynamic microphones (200-1000 ohms). ECM or condenser microphones can also be used, but they must be biased through a series resistor.

As with any mixer circuit, slight losses are always introduced. This is overcome by a final summing amplifier with a gain of 2x or 6dB. The input line levels should be approximately 200 mV RMS. The microphone input is amplified by approximately 100x or 40dB, resulting in a total mixer gain of 46dB. The microphone input is designed to output approximately 2 mV RMS at 1 meter. Most microphones meet this standard. The choice of operational amplifier is not critical in this circuit. Therefore, bipolar, FET-input, or MOS operational amplifiers can be used; for example, 741, LF351, TL061, TL071, CA3140, etc.