Here's my new Eurorack module, which I'm calling by the catchy title of Attenuvertimixer.
It's my own design, which is to say it's assembling circuits by more than one other person. (There is no new thing under the sun, to coin a phrase.) It's also a utility module, and those are always harder to explain than more straightforward things like "this one makes a noise" or "this one makes an existing noise go all wibbly", so bear with me.
The basic circuit is the attenuverter, a portmanteau of "attenuator" and "inverter". Put a signal in, turn the knob all the way clockwise, and you get the full signal out. As you start to turn the knob counterclockwise, the level drops, just like an attenuator (think of a volume control). In an attenuverter, however, the level is completely cut off at the knob's midpoint. As you continue to turn counterclockwise, the signal comes back, but inverted — a positive input voltage is now negative. At full CCW, you're getting the exact inverse of your input. The potentiometers I have for these conveniently have a stop right in the middle, so they'll click into that zero position easily. (The two trimpots on the main board are there to calibrate that zero position.)
There are two of these attenuverters in the module. Each is normalled to a +5v line, so they can output something without needing anything plugged in — it's surprised me, how often I need just an arbitrary voltage to control something else. The outputs are also normalled: when nothing is plugged into the output jack, the output is sent to the summing mixer, and plugging in to the output jack removes that signal from the mix. And since there was one more jack available, it's a plain unity input to the mixer. So you can mix together three signals, but only on two of those channels can you attenuate or invert it.
Here's a photo with the jacks labeled; I'm depending on the system coloring for telling what's what in use. (I may replace the nuts on the input jacks with some anodized black ones I have, to make things extra clear.)
So the mixer's output is in the middle, the jack with the white background behind it. The jacks above and below the pots are the ins and outs for those attenuverters, respectively. And the top jack — the one where the white background has been colored in — is the unity input to the mixer.
Plugging into an output jack removes that channel from the mix
There are refinements I might add. I'm considering having the normalled input to the second attenuverter being a copy of the first one's input; that'd yield the same behavior with no inputs, but let me easily split a signal to two different destinations, at different levels. And I would like to ultimately build a much nicer version — maybe four attenuverters, and add analog MAX and MIN outputs as well as the mixer. (Having a Maximum output is particularly useful if you have modules or devices that don't want negative voltages: just keep one channel set at zero, and then you'll get that whenever the other channels dip below zero.)
