ADHD oscillation

[rstofferahn]

Hi yall!

Pretty new to building and modding pedals. Ive done about 15 or so builds, modded about half of them.

So Ive got a question regarding the ADHD build I just finished.

I went and populated the board with the parts listed on the pcb (since there isn't a current build doc). Sounded good, but a bit bright and not much bottom end. Started with swapping out C4 (1nf) with a 10nf. Then I went and pulled C3 and added a on/on toggle to switch between the "stock" 100nf cap and a bigger 470nf cap just to see what would happen.

Sounds great, but I found that with the gain MAXED the pedal starts oscillating almost like a weird tremolo pedal, but back off on the gain just a bit and it stops. Its not necessarily a problem since I typically would never use that much gain on this pedal

My guess is the low end is overloading the TL072?

I pulled the TL072, put a socket and tried a TL082 and then a LM833n. Problem still persists.

Any ideas on what is causing it and any remedies? Obviously I can just lower the 470nf cap, but since Im still new to this...im more so just curious on what is causing this.

Thanks!

 

[jcpst]

I thought the self-oscillation was a feature, based on demos I’ve seen.

 

[Nostradoomus]

I thought the self-oscillation was a feature, based on demos I’ve seen.

I forgot I have a real OCD somewhere around here....test time

 

[Nostradoomus]

No oscillation. V1.4. It certainly doesn't sound very good though.

 

[rstofferahn]

IMG_1611.mov

drive.google.com

 

[jcpst]

I realized I mixed it up with the Acorn Amplifiers ADHD Synth Fuzz. That will self-oscillate. Not the OCD

 

[Nostradoomus]

what voltages are you getting on the IC? is it only happening with the 470n setting?

 

[rstofferahn]

I realized I mixed it up with the Acorn Amplifiers ADHD Synth Fuzz. That will self-oscillate. Not the OCD

You got me trying to find videos of OCDs oscillating LOL.

what voltages are you getting on the IC? is it only happening with the 470n setting?

i haven’t bothered measuring anything yet. And yeah it only happens when the 470n is engaged and gain is 100%

 

[Nostradoomus]

Easiest solution is just don't do that.

I don't have the schematic in front of me but it's possible you are messing with the wrong caps.

 

[rstofferahn]

Easiest solution is just don't do that.

I don't have the schematic in front of me but it's possible you are messing with the wrong caps.

https://docs.pedalpcb.com/project/Schematic-ADHD.pdf

lol yeah, I never max the gain on an ocd anyways.

I got the idea from the “bandwith” on the eqd dunes/palisades (oasis/stockade), increasing the low end into the drive section…or at least that’s how I understand it lol

 

[Nostradoomus]

It sounds like it is but that could very well be destabilizing it at such a high value