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I'm not a real engineer either. Best to try this on a bench or in a simulator, check for stability and so on.

R2 can go as low as U1 can comfortably drive without distorting, so probably not much less than 1k if you're using a TL07x. At the other end of the range, I probably wouldn't go over 5k to keep the noise low. When choosing a P2 value, keep headroom in mind. 1+ P2/R2 is the U2 gain, and too much...

I don't see why precision opamps (low DC offset) would make a difference. You can change the C2 value to whatever you like. It just gets multiplied by 1 + P2/R2.

I would actually use a dual opamp in real life. The only reason you see 2x OPA196 in the schematic is that I did it in a simulator and there are no dual opamps there. TL072 ought to work fine, too, if you're not into SMD.

Thank you! I was today years old when I realized, thanks to you, that I could just use a wav file as the input to a circuit simulation (in my case, TINA-TI) and record its output back to a wav file. D'ooooh! Why didn't I think of that?? Who even needs to actually build physical stuff anymore...

I am having a hard time imagining the use case for a balanced in/balanced out pedal, especially one that would need a true bypass. Please tell us more.

I'm afraid I can't help, I don't use LTSpice.

If you want a high input impedance op amp stage, you'll always want to go non-inverting for low noise.

There's no reason for R23 and R36 to be any higher than around 10k. They make noise. The higher the value, the higher the noise. Don't just jumper them, as suggested above, or the circuit won't work at all. In several places, you have RC filters that will significantly roll off the lows (C6-R6...

^ I can't disagree 😛

I have a little concern. In several places, you have 4.7uF caps tied to some DC voltage via 1M resistors. After powerup, those would take quite a long time to find a stable DC operating point, wouldn't they? The time constant is on the order of seconds. Does the circuit work right away when you...

If it does it mostly at startup and it gets progressively better over time, it sounds like a bad electrolytic capacitor to me. Though I must say I've also seen a few op amps do that... If you have some Freeze Mist around, it could help with narrowing down a specific component.

Plug the whole circuit (or just a section, for starters) into a Spice simulator (I use Tina-TI). Do a noise analysis. Tweak, repeat. This is how I learned about noise optimisation. Just make sure you have good Spice models for your active parts, that take their noise into account. Here's a...

Nice! Been there, liked it. Shediac. Very nice beach (you can even go in the ocean without running into an iceberg for maybe a month a year 🤪). Best chowder I've ever had.

^ I take it that you have Canadian ancestry?

Almost a year after I suspended shipping to the US due to tariffs, I finally gave in and went through the bureucracy of having my products USMCA-certified (or CUSMA as we call it in Canada). It took all of 15 minutes or so, all online. I also have to label my stuff Made in Canada (which is...

^ There are many small, cheap, pluggable headphone amps out there, such as the Vox AmPlug series (they suck - that's why I designed this!). How many people would want to pay more for an onboard one with no FX? Even if mine lasts 10x longer on a battery, gets way louder before clipping, and it's...

I'll probably publish it in some magazine, since nobody wants to buy it anyway :) There nothing to it, except for the right choice of component - which is absolutely key. But I'm probably on the wrong forum for this. It's a low power design, and pedals don't really care much about that.

I keep working on and improving an onboard headphone amp I designed. I think it really whips the llama's ass. I use it all the time at band practice (private in-ear monitoring, straight out of my bass - I ALWAYS hear myself), at home to practice along music (it has an aux in), and so on. Nobody...

I swear, there's a thick mane of luscious hair under that cap 😜