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FET Audio Mixer Circuit

This FET audio mixer is an example of FET’s versatility. FETs are originally designed for high frequency applications but they can be used for audio frequencies and in fact they perform excellently in this area.
This mixer needs only four FETs and performs very well (actually you cannot expect a high quality mixer).

The mixer’s input impedance is determined by the resistance of the input potentiometers used, since the impedance of the FETs is very high.

The number of inputs that can be connected to the circuit is unlimited as long as the R1 value is chosen according to this formula: R1 = 22K / n, where n = the number of inputs.

The frequency response of the audio mixer is from 20 Hz to 80 kHz and linear within 3 dB

FET Audio Mixer Circuit Diagram

fet mixer circuit diagram

Audio Mixer Components

C1 = 0.1 uF/50V ceramic
T1 … T4 = 2N5397, 2N5398, 2N5486, MPF102, MPF106

2n5397-5398-5486-mpf102-106

Audio mixer pcb

fet-audio-mixer-pcb

3 Comments

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  • David Gomes

    What could I change in this circuit to use a 9V battery? I want to use it in an accordion. Is it possible?

    • Jim Keith

      I think that it should work OK at 9V provided that the signal levels are kept low. Audio output signal level for low distortion should be in the range of about 10 to 100mV.

      Additional info:
      Idss (drain current with gate shorted to source) should be reasonably matched for T1, T2 & T3. This parameter tends to be sloppy, so you must test a few devices in order to find some that are reasonably matched.

  • Jim Andrews

    Will this design work from 12v?

    I’m looking for a mixing solution for equipment that is running from 12v only (unless I use an inverter, but don’t want to go to that complexity).

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