Hi. Here’s something I’ve been working on: a prototype for a panning mixer, as previously seen in Minimal mixers, and here realized as a 3HP Eurorack module. This is work in progress, but I thought it would be nice to keep a bit of a log of it.
To recap, the idea is to have some number of input jacks (seven, here) mixed down to two output jacks, with each input representing a fixed pan position somewhere between the two extremes represented by the outputs. Plug a signal into the topmost input to send it entirely to the top output, the middle one to send it equally to both, etc.
This can be implemented by a very simple circuit - little more than two inverting-summing amplifiers of the kind you’re likely to find in any electronics textbook (e.g. Horowitz and Hill, p. 234), with unequal input resistor values, and followed by unity-gain inverting amplifiers to get the phase right.
I designed a schematic and board layout in KiCad, and, in a personal first, got proper boards made, at OSH Park. Would have preferred a single-board design, but not enough to compromise the panel layout, hence the small backpack board for the power connector and op-amp.
The panel is mill finish aluminium (couldn’t find reasonably-priced anodized in sub-industrial quantities in Sydney, where I live) that I CNC’d and went over a few times with a scouring pad (hat-tip), and then scratched anyway. I used electrical tape to mark the output jacks.
So, what now? Well, now that I have this thing mounted in my system, I’m going to spend a few weeks playing with it. See what needs to be tweaked, figure out if the concept makes sense in practice, etc. Name it, maybe.
Thanks for all the feedback and suggestions in the original thread! (Quick summary: width knob, per-input gain knobs, output jacks on opposite ends, stereo headphone output.)
Lots to think about, and while I certainly have opinions, I’ll put them on the shelf until I’ve had a chance to test how this thing feels in practice. To be clear: thoughts, comments, suggestions and questions are all very welcome.
What I will say, however, is that once I’m happy with the design, I’ll open-source it, simple as it may be. Happy for anyone to adapt it to their own needs.