#1

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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.

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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.

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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.

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#2

Thanks for the great work and contributing it to the community. I love it and can’t wait to see how it goes for you. I’d love to add something like this to my setup.

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#3

I will echo the sentiment above, and say that I sincerely hope to one day have one or two of these in my cases.
Brilliant idea, and a beautiful execution!

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#4

Wow! I want one! It’s a terrific idea and while the 3hp size seemed odd (sorry :slight_smile: ) at first, when I saw the pic in the Make Noise skiff it all made sense: that little fu*ker is 105hp instead of 104 so it starts to sound very clever, and it’s in that skiff that it will end.

Send me a pm, I’ll send you the dough. :slight_smile:

#5

Great concept! Must be hard with those suggestions, too, but perhaps it could be explandable? Like, different 3hp expansions that could perform each function? One that has the width knob and headphones, one that has per-input gain knobs. Just a thought!

#6

Again, I love this.

I’d take two, obviating the 3hp problem (not a fan of odd sized panels generally…damn you Elby! :slight_smile: )

Would changing resistor values change pan position? Seems so. My preference would be for one that has as many fine pan positions as possible (no hard lefts or rights), and one that has say three centered and the rest more coarse pan positions.

A bus on the back to connect two could be fun, but not necessary.

I’d gladly take this with the plain milled panels. Preferably actually! Nice idea with the electrical tape too.

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#8

Too bad SirMixALot is taken already.

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#9

@billyhologram Would love to build one if you have a pcb left! Still have a 3hp blank which I can use for this.

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#10

also interested in this - great job! Panning independent to clouds is still very real problem in my set up.

#11

Love this idea. I would definitely be interested in whatever the final product evolves into.

#12

Same here – would love to buy one, as I am of no use at a soldering iron.

#13

This looks simply beautiful! :heart_eyes:

I’d love to build 2 or three of them with individual widths, one to spread the Verbos HO in space. What a nice idea!

Good that PCB’s from OSH Park come in packs, really looking forward to experiment with it!

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#14

Yes!
Me too!
Me too!

#15

This would definitely interest me if it was in 1u format, just a thought.

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#16

@billyhologram - this thing is damn clever. Thanks for working on it and being so willing to share. Cheers!

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#17

Nice! This plus a sequential switch (WMD SSM) would be pretty neat.

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#18

I had a vague idea about using this to turn a few similar voices into a single thick stereo voice, but hadn’t thought about using it with a harmonic oscillator! Could be gorgeous. I imagine it could also work well with, say, Three Sisters, or a multi-tap delay.

Nifty! A voice moving from one side to the other in discrete steps, or, if you jumble the cables, skipping around from spot to spot.

Yes, absolutely! Technically, each input gets sent to two buses, with gains set by the corresponding resistors. You can think of this as panning, or you can think of it as just that. By tweaking the values, you can adjust the pan law or the spacing of the pan positions. Or, say, make the signals more attenuated the further they are from the center, if that’s your thing.

My plan is to find good resistor values for a vanilla build, but also to do a proper write-up on picking alternative ones in the build guide.

I will think a bit about expanders and such. Could be good, but not sure how much more I can fit on the PCB without making it wider.

Speaking of which, I will need to revise the board layout at least once. Between my slow pace (full-time job-having new dad here) and OSH Park shipping times, it will be at least a month before that’s done and tested.

I am blown away by your enthusiasm for this project, and am really keen on getting it done and sending it out in the world, and see what you all do with it. It’ll just be a little while.

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#19

Just wanted to add my voice to the encouraging crowd. This looks great. The simpler the better as far as I’m concerned. Definitely interested in picking one up, DIY or otherwise. 3hp will help me use up the extra 1hp that’s appeared in my rack since switching to sliding nuts! Looking forward to following how you get on

#20

It might be useful to compare / contrast this with Cold Mac?

#21

I keep daydreaming about chaining them together via a jumper cable in the back so that the outputs mix in with an adjacent unit - unless they are patched. This would allow for a single output pair to have the sum of multiple mixer modules without patching - keeping the patch points open for more instruments.

But - they are exceedingly awesome as-is as one can patch to the hard points between units. (Though, this would be at the loss of hard-panned any instruments outside of the first unit in a chain.) :slight_smile: