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Design the circuit for low current draw. There are good dual op amps amps drawing 0.2 to 0.3mA (as in, at least as good as TL072) but they're SMD-only.

11M? That's not even a cromulent value! Who the hack uses 11M? Booo!

Cool! The rest of the noise you're getting could probably be fixed by shielding your circuit. Try a sheet of aluminium foil under the breadboard (make sure you ground it). Maybe put a sheet of paper between them to avoid any shorts. I use this method a lot when I measure my circuits, so the...

Yeah, the parallel 100nF is more of a "good practice" than anything. Nothing beats a simple resistor followed by a chonky elcap.

Set your meter to mA DC and (somehow) insert it in series with the power supply. OR: If your pedal already has a series resistor (such as 100 ohm, or 22 ohm or whatever) right after the DC input jack, you can measure the voltage across this resistor (V) and compute the current using Ohm's...

A 100 ohm resistor followed by 100uF (or more) to ground (maybe in parallel with a 100nF, which works better at higher frequencies) would kill all but the most egregious noise coming from a power supply. Just as long as your pedal doesn't draw a lot of current, in which case the 100 Ohm resistor...

Would be cool to see a 3d view. You do have 3D models for all your parts, right?

I wish I had read this a few years ago, before I spent a whole week basically figuring this out for myself the hard way. Another thing that helped was to pick an op amp that was relatively slow and low-power. TL062 worked well for this.

Um... where's your ground pour?

I usually just input the schematic into a circuit simulator and see if it works. I might place virtual scopes/meters/spectrum analyzers/signal generators around the schematic and compare with what the physical board does. After I discovered circuit simulators I almost stopped breadboarding. As...

^can't that be turned off in the preferences?

Very true. When doing psychoacoustic experiments we go to great lengths to match levels very accurately (to small fractions of a dB). Louder is almost always perceived as sounding better - even if it's the exact same source, just played 0.5dB louder. Consider that a great studio speaker...

BBD biasing for lowest distortion might fix it, if you haven't already done that.

What do you print the top label on? Unrelated hint: OPA2196 and OPA2990 are good options for guitar/bass headphone amps, especially if battery powered (super low idle current), as long as you use a series resistor on the output. Something like 20 ohms or more.

Rest assured that audio can be analyzed way, way beyond any human's ability to hear, just as technology obviously exists to see tiny things far beyond what the human eye can see. Now, how that translates into terms like "this sounds thin, or grainy" or such, I don't know. These terms are...

^ Exactly. We do this kind of stuff all the time. Pulling up faders that aren't even assigned to anything, tweaking knobs that do nothing... Then laugh our asses off after everyone's gone 🤣

^ oh yes, the technology (and methodology) to prove/disprove audio perception very much exists. The problem is that people often don't want to accept the results if they contradict their preexisting ideas. If you think something sounds good, or different from something else, then it will sound...

Enlarge your ICs with this handy timer:

Well, it looks great, so it failed successfully!