You cannot build a modular without any mixer modules. I’ve made quite a few mixer modules by now and I noticed I hadn’t put anything up online. So, I’m rectifying this oversight with this post.
Mixers are a whole world onto itself and quite a rabbit hole if you dive into it. However, in Eurorack land things are generally pretty simple as a mixer doesn’t have to deal with a wide variety of signals, routing options, EQ’s and all that mumbo jumbo. It’s pretty much known what will be received in terms of signal, making a lot of what goes into a good mixing desk unnecessary.
So, as a result, Mix-01 is almost as bare-bones as you can build a mixer. A single dual opamp is used where one part is the summing mixer with a gain of 1:1. Since that uses an inverted opamp configuration the second opamp is used to revert the signal again to keep the phase of the signal correct. I’ve used a TL072 as an opamp because it’s fairly decent, cheap and I had them lying around, but you can swap it for a better one if you are so inclined, but generally speaking, the TL072 should be fine for this purpose.
This schematic should be fine mixing CV voltages as well. You might want to use linear pots for such a job instead of logarithmic ones preferable for audio purposes.
I’m working on a more advanced mixer design. Since my modular system keep growing more and more simultaneous voices are being generated purely on the modular. So there is more need for some kind of ‘output’ mixer with a little more bells and whistles then just the few simple signal mixers – like the one in this post – scattered around the system.