Jul 142016
 

Microphone Mixer using operational amplifiers

This Microphone Mixer using operational amplifiers combines signals from 3 different sources (3 microphones) easily and economically. This mixer can even work as an amplifier and portable mixer because of its few components.

How the microphone mixer work?

The circuit uses two operational amplifiers as main elements. The first operational amplifier works as a signal mixer and receives at its inverting input, the three signals from the microphones.

Microphone Mixer using operational amplifiers

We can adjust the amplitude (volume) of each of the input signals using the R4, R5, R6 potentiometers. This, prior to amplification of the combined signals, that makes the first operational amplifier (U1). The output signal of the mixer is applied to a small network of resistors, potentiometers and capacitors in order to obtain the controls to adjust the sound.

The signal is subsequently applied to another operational amplifier, configured as voltage follower. This allows the output impedance of the amplifier to be very low. To prevent external noise affecting the circuit, is placed on each power input (-9 volts and + 9 volts) a capacitor. See diagram.

This simple circuit allows us to have a portable audio mixer that uses two 9-volt batteries

List of components for the microphone mixer circuit

  • 2  741 operational amplifiers (U1, U2)
  • 3  1K resistors, 1/4W (R1, R2, R3)
  • 3  10K logarithmic potentiometers (R4, R5, R6)
  • 1  1M resistor, 1/4W (R7)
  • 2  10K resistors, 1/4W (R8, R10)
  • 2  100K linear potentiometers (R9, R11)
  • 4  0.1uF ceramic capacitors (C1, C2, C5, C6)
  • 2  22nF ceramic capacitors (C3, C4)
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