Eurorack CV/Audio Attenuverter/Mixer

Last Update: 11/7/2022

The Eurorack Breadboard Power module attached to a breadboard

I hope you like spelling mistakes! Making the front panel for this module was a lot of work, so I'm just accepting that is says "Adio".

For some time now I have wanted to build my own eurorack modules. I've done a couple of the DIY kits that give you a PCB and all the necessary components but this didn't quite scratch myt DIY itch. I wanted to build ny own circuit using perf-bord or a PCB of my own design, and I wanted to make my own front panel. For this project I went the perf-bord route, and I laser engraved anodized aluminium for the front panel.

What is a mixer?

A mixer simply takes two or more signals and adds them together. For audio this would allow you to hear multiple notes at once to make a chord. For Control Voltage(CV) you can mix signals together to make a signal with a more complex shape.

What is an attenuverer?

Attenuverer is a portmanteau of the words attenuator and inverter. For audio attenuation is synonymous with making it louder or quieter. In a mathematical sense it can be thought of as multiplying the signal by a scalar usually from 0 to 1. An inverter on the other hand will take a signal and basically multiply it by -1. This function is more useful for control voltage than audio. Overall, I usually think about attenuverers mathmatically they multiply the signal by some ajustable value between -1 and 1.

The Eurorack Breadboard Power module connected to a volt meter showing 23.8 volts

In the early months of this year (2022). I stumbled upon this design for a Quad Attenuverter/Mixer made by kassutronics. Essentially, this design provides four attenuverters but the clever bit is how it takes advantage of switched output jacks. If you plug a patch cable into any of the attenuverter outputs you'll get the input but attenuated. However, any outputs that do not have a cable plugged in are instead added together (with the sum input as well), passed through an attenuator and finally output at the sum output. The reason I was excited by this design is its versatility. Not only can it serve as an attenuverter or a mixer, but it can do both at the same time. For example, you could use two of the attenuverters to attenuate some CV signals and the other three inputs to mix audio together.

I set out to build this circuit on some perf-board which only took a few hours. The real challenge I had was figuring out how I would make the face plate so that the holes would line up with the components. after several paper and wood prototypes I was able to laser engrave the panel and drill holes in the appropriate spots.