DC Mixer

This is a DC mixer module. There’s not much to say beyond that! It takes up to three DC coupled inputs and mixes them down to two outputs, one inverted, the other not. Besides attenuators on each channel, there is a level (gain) control. This allows you to mix large signals without clipping, and without having to limit the range of the input attenuators. There also is a bias (offset) control that lets you add a positive or negative constant voltage to the output. This mixer is intended mainly for use with control voltages.

Note that the offset is effectively added after the gain and inversion (internally it’s more involved than that, but that’s how it behaves). So a +5 V bias is +5 V regardless of the gain setting, and it’s +5 V for both the inverted and non inverted outputs. This means if you take a ±5 V input, reduce the gain to ½, and add a +2.5 V offset, you’ll get a 0 to 5 V result on both outputs.

Schematic:

Schematics, KiCad design files, Gerbers, documentation