Need help troubleshooting a PedalPCB Pendulum kit I modded

[airvian]

So I built a PedalPCB Pendulum. Didn't like it. I added in a GuitarPCB Buff N Blend circuit. Worked fine. Liked it. I built another one in a smaller enclosure and am now only getting buzzing at the same rate as the tremolo speed is set (when mounted inside the enclosure or not). IC Output at all IC1 pins is fine except pin 8 (where I get the buzz that goes to the output) as well as the pins of the volume pot that goes across pins 8 and 9 of IC1 (checked with audio probe). I wanted to put the one that worked into a smaller enclosure too but it got the exact same fault now (also mounted and non-mounted). I also switched out the volume pots from a B100K to an A50K in both. Bypass works fine in both. Turning down the mix control of the Buff n Blend when the pedal is engaged does not help. One of them started working when I tugged at the blend pot, so I replaced those wires which did not help (It doesn't work when tugging at it anymore now though). Turning the volume knob and setting it at other levels than all the way up or all the way down makes the pedal make terrible screeching buzzing noises as well (also on both). Any help on where that could come from would be highly appreciated.

https://www.pedalpcb.com/docs/PedalPCB-Pendulum.pdf
https://guitarpcb.com/wp-content/uploads/2018/06/Buff-N-Blend-v2-2021.pdf

[antonis]

Have you verified R7 & R8 resistors proper values..??

[airvian]

Have you verified R7 & R8 resistors proper values..??

Yes. All components are the correct value except for two mods: the output cap is 47nF instead of 1uF and there is a 4.7nF cap across the lugs of the volume pots. What is puzzling me is that both builds have the same problem. The first right after building it for the first time, the second after pulling it out of the old enclosure and into a new one (then independent of being in an enclosure or not). All the mods are verified and working on a prototype I did.

[antonis]

the output cap is 47nF instead of 1uF and there is a 4.7nF cap across the lugs of the volume pots.

47nF cap forms a HPF with 10k shunt resistor of about 340Hz cut-off frequency..
That frequency happens to be the same with IC1.3 LPF (4.7nF cap across 100k pot) for Volume pot maxed..
(BTW, that pot actually serves as "Gain" pot, but let it be..)
For any other pot setting, LPF cut-off frequency increases so it actually is the 47nF/10k HPF the one which sets the lower frequency of the band..
e.g. for pot 50% setting, you have a band-pass filter of 340Hz to 677Hz..

What's puzzling me is what about "dead zone" (400Hz - 1950Hz) between R6/C3 LPF and R5/C2 HPF..

[airvian]

the output cap is 47nF instead of 1uF and there is a 4.7nF cap across the lugs of the volume pots.

47nF cap forms a HPF with 10k shunt resistor of about 340Hz cut-off frequency..
That frequency happens to be the same with IC1.3 LPF (4.7nF cap across 100k pot) for Volume pot maxed..
(BTW, that pot actually serves as "Gain" pot, but let it be..)
For any other pot setting, LPF cut-off frequency increases so it actually is the 47nF/10k HPF the one which sets the lower frequency of the band..
e.g. for pot 50% setting, you have a band-pass filter of 340Hz to 677Hz..

What's puzzling me is what about "dead zone" (400Hz - 1950Hz) between R6/C3 LPF and R5/C2 HPF..

Yes. Thiis is the reason for the change of the B100K Volume pot to an A50K due to excess gain otherwise and unity at very low pot settings. I have attached a couple of pictures. Please let me know if anything sticks out to you.
What do you mean by the dead zone?

[antonis]

Almost all wire-pad joint need reflow and wiskers cut..

Especially, the one bellow is prone to almost everything..
(from signal mute to lunatic oscillation..)

[duck_arse]

the TL074 is a "better" opamp for audio than the LM324. the LM324 is a good choice for oscillators, being lower power than the TL074. I'd say swap IC1 and IC2. won't fixxe, but won't hurt.

[airvian]

the TL074 is a "better" opamp for audio than the LM324. the LM324 is a good choice for oscillators, being lower power than the TL074. I'd say swap IC1 and IC2. won't fixxe, but won't hurt.

Sadly the issue is independent of the chip I use. I've mixed and matches several I have laying around, all showing the same issue

[airvian]

Almost all wire-pad joint need reflow and wiskers cut..

Especially, the one bellow is prone to almost everything..
(from signal mute to lunatic oscillation..)

I've fixed that. However, it did not really help. Sometimes it works when I plug the guitar straight into the effect but when I plug it in the signal chain it doesn't. But it is not consistent sadly. I've made an audio recording of the issue with me turning the volume pot up and down:
https://drive.google.com/file/d/1KBztx2az74KxhNWplAK2c_5_bQ3rkp4Y/view?usp=sharing

[idy]

Audio probe? Haven't lived 'till you've tried one. Saves much head scratching and even hair loss.

Why the 4.7n "across" the volume/gain pot? Sounds crazy to me. It is really a negative feedback loop for the opamp. In places where we do *that* it is usually in the picofarad range to "round the corners" on high gain clipping type circuits, not kill all frequencies above 340hz. (Killing them softly because 6db per octave, but still, funny idea.)

[airvian]

Audio probe? Haven't lived 'till you've tried one. Saves much head scratching and even hair loss.

Why the 4.7n "across" the volume/gain pot? Sounds crazy to me. It is really a negative feedback loop for the opamp. In places where we do *that* it is usually in the picofarad range to "round the corners" on high gain clipping type circuits, not kill all frequencies above 340hz. (Killing them softly because 6db per octave, but still, funny idea.)

The audio probe is my main troubleshooting tool. I've now found the main problem by accident (twisting the power plug around) to be the power jsak, which i replaced. Now the only remaining issue is a relatively loud background hiss. It isn't the kind of buzz you get from a missing ground or sth similar but more of a constant crackle.

The idea behind the cap across the volume/gain pot is to do exactly what you described. The lowered output cap value is to reduce the bass (which is frankly ridiculous in this circuit), the cap across the volume pot is to kill any possible shrillness (just ended up with this solution from tinkering around with the unmodded circuit initially. I bet there is a more sophisticated way to do that)

[deadastronaut]

for a moment there i thought it was my ''pendulum'' tremolo+ circuit design 2019.   

anyway, as you were...

[airvian]

for a moment there i thought it was my ''pendulum'' tremolo+ circuit design 2019.   

anyway, as you were...

Haha... nono, it's a PedalPCB one