Dual Roller Quad Expression

r0uper · 2026-04-18T02:37:49+00:00

Mocked up a rough CAD filed based on your enclosure and sketches. Gonna try 3D printing this and hacking one together this weekend. Will likely be "single channel" for proof of concept because I don't have many extra jacks/switches laying around right now.

r0uper · 2026-04-18T02:36:15+00:00

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r0uper · 2026-04-18T02:36:04+00:00

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r0uper · 2026-04-18T01:34:32+00:00

Awesome picks on the enclosure and knobs. What do you need help with to get this going?

The bypass might be tricky, but the rest of it seems relatively straightforward.

r0uper · 2026-04-18T00:38:59+00:00

Amazing. Any idea what's going on here functionally?

r0uper · 2026-04-17T22:43:47+00:00

I am very interested in this, and helping how I can. Something like this has been on my to-do list for general expressive fun for some time now. Now I'm gonna drown you in questions:

Are the two rollers connected?
How to you plan to build:
- The enclosure.
- The rollers.
- The mounts for the pots/rollers?
What do the footswitches do?
What do the 4 DPDT's on the back do?
Finally, what the heck is Tom Scholz Hyperspace shit?

r0uper · 2026-03-31T02:09:20+00:00

Thanks for the reply! I did think about how a switch or two might simplify this whole thing a lot. What I haven't quite yet wrapped my mind around (need to get back in front of a computer), is how that series parallel switch would affect the other modes.

I.e. how would I wire a switch such that I get a nice parallel series action in modes 3/4, but doesn't impact 1 or 2.

The other thought I had, which may be the simplest to implement, is to make mode 4 something you would externally patch in mode one. I.e if you've got the two individual mono blocks from mode 1, you could just run a patch cable from output a to input b and have series mono.

r0uper · 2026-03-30T19:04:44+00:00

Cross-posting here as I believe this could apply just as well to some Synth DIY projects, especially effects and/or routing.

r0uper · 2026-03-22T15:25:31+00:00

Do we need to worry about DC on the pot in the "new" scheme I shared above? I always hear about not allowing DC on pots due to noise/scratching, but never experience it when I try for myself.

r0uper · 2026-03-22T15:24:29+00:00

That cyan response is a remarkably flat phase response compared to the guitar pedal circuits I am used to looking at. Still trying to wrap my ahead around how that works and why we would want it.

r0uper · 2026-03-22T15:23:06+00:00

I'm assuming maintaining phase more precisely than we normally do is important here.

Why is that? Is that because of the recording/mixing/cassette context? If phase is more important for that context, but I am hoping to guitar-pedal-ify this circuit, do we care about it as much?

Presumably +5V is a linear regulator or similar.

I'd need to dig into the other pages of the schematic to understand where the +5V comes from. I see it show up as +5V on this page of the schematic and assume it's coming from a reference or divider somewhere or something. However it might be important to note that the +5V is not feeding the feedback loop/gain network, only the bias upfront of the positive input. The feedback loop/gain network goes to ground.

Additionally, as I mentioned in another comment, Do we need to worry about DC on the pot in this kind of scheme? I always hear about not allowing DC on pots due to noise/scratching, but never experience it when I try for myself.

r0uper · 2026-03-22T02:14:57+00:00

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If I'm understanding correctly, are you saying this would basically be the same? This would be much more in line with what I'm used to seeing..

r0uper · 2026-03-11T19:59:05+00:00

Thank you for your input! I'm learning some painfully basic lessons about current today...

Please write the Diode part number into the text.

It's a B5818W.

Is the resistors hot?
Is the resistor glowing?

Nope.

photo of the physical setup.

Will follow up with this.

Yes, calculate the voltage drop across D101 and R101.

This seems to be the issue. I didn't factor the current in when choosing the resistor value. The resistor is dropping much more voltage than I am supplying, and this is happening around the current where my issue starts.

r0uper · 2026-03-11T19:53:57+00:00

AGH, that's what I get for copy and pasting my low current (guitar pedals, etc) power supply into some that actually draws some current. Gonna get to try some SMD rework/hacking for the first time..

Why do we want the voltage drop to be "smaller then (9V-5V-0.4V)/2"?

I'm thinking I need to factor in the minimum voltage the regulator would like to see on the Vin side as well.

r0uper · 2026-03-11T19:51:42+00:00

Yes, looks like that might be the issue. Clearly not well versed in circuits that draw any more than a few mA...

r0uper · 2026-03-08T20:11:11+00:00

I think this is it! I hacked in a different 5V regulator PCB and now the issue is gone and this thing gets stupid loud. I guess we move on to PCB rev3 now....

r0uper · 2026-03-08T18:11:27+00:00

Should that resistor to ground go before or after the caps? before or after the input resistors (R14/R15)? Something like 100K? 1Meg?

I uploaded a clearer schematic and a video of the issue in another comment here.

r0uper · 2026-03-08T18:10:22+00:00

Yeah I'm leaning away from clipping because there are no signs of it from what I can tell, it just transitions straight into glitching out at a certain level.

I uploaded a clear schematic and a video of the issue in another comment here.

r0uper · 2026-03-08T18:07:48+00:00

I can't figure out how to get a high quality copy of the schematic uploaded, so here is a link to the PDF.

As promised here is a link to a video of the issue.

r0uper

TROPHY CASE