Utility Mixer I


Utility mixer front view.

This is an often used utility module. The mixer comes in handy for mixing CV sources. The mixer is DC coupled, so you can use it for DC and AC mixing. The input impedance is constant 1MOhm. The input signals are amplified by a factor of two. It is possible to offset every input with +/- 5V. The offset is signaled with diodes for every channel and for the summing output. The outputs are normalized, so you can remove selected channels from the output mix. The summed output has a -6dB switchable attenuator. There is an inverted summed output added as well. The added volume indicator us useful for finding the appropriate signal level.

Specs and features



Utility mixer schematic control board

Utility mixer schematic: Control board

Utility mixer schematic main board

Utility mixer schematic: Main board


Control board: Straight forward design. The mixer is completely DC coupled. So you can use it for CV mixing as well as audio mixing. IC1B,C,D buffers the three inputs and and keeps the input impedance constant. P2, P4, P6 sets the amplification from zero to 2X. P1, P3, P5 sets the offset voltage. The LED indicates the offset and signal level.

Main board: IC3B, IC4B, IC6B adds the offset voltage and the signal. IC1C, IC1D, IC1B, IC1B drive the low current LED. IC2A sums the signals and drives the negative output. IC2B drives the positive output.



  • Set the input potentiometer to zero, the offset potentiometer to center. Measure the output voltage at each channel. Adjust TR_1, TR_2, TR_3 to zero Volt.

Building hints

  • You can leave the level indication LED out with no problems for the other functions.

Special parts

  • Use center detent potentiometer for offset voltage.


Utility mixer control board documentation download
Utility mixer control board Gerber files download
Utility mixer main board documentation download
Utility mixer main board Gerber files download
Utility mixer .fpd file

Utility Mixer front view

Utility Mixer: Front view

Utility Mixer populated control PCB

Utility Mixer: Populated control PCB

Utility Mixer populated main PCB

Utility Mixer: Populated main PCB

Utility Mixer side view

Utility Mixer: Side view

Utility Mixer back view

Utility Mixer: Back view

2021 January V 0.9.5-EB

2021 January V 0.9.0-EF

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