Three Skeptical Buffers, three switches popping

[Kroars]

I really hate to do this. I recently had an issue with a TS808 popping, that @music6000 kindly pointed out that I had an incorrect resistor installed. In that thread I had mentioned that I had a Skeptical Buffer doing the same thing. After replacing the usual suspects for leaky caps (all checked out, but replaced anyway), I went one by one replacing every component on the pcb, including footswitch, all jacks and wiring.

I ended up ordering two more Skeptical Buffers, just finished them and they pop as well. One a lot louder than the other. I’m hoping someone can spot something that I’m missing or suggest a fix. Here are the three SB’s that are popping. I suppose I can Orman’s fix with the additional resistor and capacitor at the LED, but I’ve got to be missing something here.

Robert mentioned in one thread about a Cobalt popping “2M doesn't allow any DC bias to discharge from the 10uF capacitor quick enough”. I wonder if there is a similar issue with the 3M3 prior to output? I don’t see a schematic posted for this, though.

Thank you very much for any help.

 

[Kroars]

Tried a 10k from ground to output on the 3pdt. Nothing changed. Added a 10k to input from ground on the 3pdt and it got way better. Pop still there, but much less pronounced. Hopefully I’m on to something…..

Also noticed the pulldown resistor on the 3pdt needs to be from middle lug (5) to top lug (1 for input, 7 for output). Although, as mentioned, a 10k from ground to output didn’t change anything. A 5.1K from input to ground was even better, but I’m unsure if a lower value would create any difference in the sound?

 

[Kroars]

The pulldown resistor added to the 3pdt on the input side did help the pop, but it also sucked the life out of the pedal…. So that’s not an option. Here is a picture of the back of one of the pcbs. I don’t see any cold solder joints, nor any debris that could cause an issue. Anyone else?

 

[music6000]

1. Are you usingTantalum caps in the spots marked for Electrolytics with the correct polarity?
2. What Brand or model are the Electrolytics & is this what you regularly use in other Builds?

EDIT: I looked at your previous Builds & most of those use the Gold coloured Electrolytics.
Even the TS808 used Gold ones!
The Blue ones look new to your Skeptical Builds???

 

[Kroars]

1. Are you usingTantalum caps in the spots marked for Electrolytics with the correct polarity?
2. What Brand or model are the Electrolytics & is this what you regularly use in other Builds?

EDIT: I looked at your previous Builds & most of those use the Gold coloured Electrolytics.
Even the TS808 used Gold ones!
The Blue ones look new to your Skeptical Builds???

Yup. Correct polarity for the tantalum’s. The blue caps are part of a batch of 500. They’re Nichicon UKT’s from Mouser. I’ve used approx 200 of them on other builds without issue. They’re audio grade and read less than 1 ohm ESR. One on of the skeptical buffers, I pulled all the electrolytic caps and replaced them with tantalum (except for the 100uf). Still a pop.

 

[music6000]

This may work or have no impact at all. It seems a crazy value but others have built it successfully with 3M3.
Try changing the 3M3 on the Output to Ground for 100K.
3 in a row all doing the same thing seems strange.

 

[music6000]

Can you confirm the Cap on the bottom left is 3pF ?
If it is silver mica, what is the voltage?

 

[Kroars]

This may work or have no impact at all. It seems a crazy value but others have built it successfully with 3M3.
Try changing the 3M3 on the Output to Ground for 100K.
3 in a row all doing the same thing seems strange.

Yeah, I’ve built a couple before with no issues, using the same batch of parts. I’ll try the 100k in place of the 3M3 on bottom right of pcb. The cap is a 100v 3pf. I thought that may be an issue as well and put a 10pf Mlcc just to check. Still a pop. Thank you for your help with this.

 

[Kroars]

Tried replacing the 3M3 resistor on output to 100k, still have loud pop. Tonight I’ll try the same on the 3M3 at input

 

[Kroars]

Update, tried 1M, 100k and 10k in place of the 3M3’s on input and output. Once again, the output side didn’t change much. With a 10k in the input side, the pop noticeably decreased. Although, it also introduced a bit of noise when the circuit was activated.

I’ve built a handful of other pedals with the same batch of components without issue, since starting these three SB’s. I’m out of ideas.

 

[music6000]

Can you try a 4558 or OPA2134 in a stock build?

 

[DailyDovetails]

Perhaps a long shot but on the one pedal I have build that pops noticeably to me the Thermonic distortion. The proximity of the wires to the board and each other seems to affect the loudness of the popping I keep meaning to go back and shield it to see if it goes away. That being said. Have you tried to move this wire away from the board here to see if it gets quieter?

 

[Kroars]

Perhaps a long shot but on the one pedal I have build that pops noticeably to me the Thermonic distortion. The proximity of the wires to the board and each other seems to affect the loudness of the popping I keep meaning to go back and shield it to see if it goes away. That being said. Have you tried to move this wire away from the board here to see if it gets quieter? View attachment 72428

Thats a great suggestion, thank you! Although, the one I’m testing is out of the enclosure and the other handful of these I built have the same wire route, without issue. Perhaps I’ll use shielded wire, just to give it a shot. Thanks again!

 

[Kroars]

Can you try a 4558 or OPA2134 in a stock build?

I’ll give it a shot. I did use a couple TL072’s, and definitely have used others (in other builds) from this same batch I got from Mouser, but it’s worth a try. I’ll let you know.

 

[DailyDovetails]

This thread https://forum.pedalpcb.com/threads/missing-build-docs-schematics.3784/page-53#post-213182 has a schematic trace for this board and it shows that R13 is possibly a 100K resistor.

Maybe try a higher value and see if it help?

 

[Robert]

This thread https://forum.pedalpcb.com/threads/missing-build-docs-schematics.3784/page-53#post-213182 has a schematic trace for this board and it shows that R13 is possibly a 100K resistor.

Definitely 10R.

 

[music6000]

I’ll give it a shot. I did use a couple TL072’s, and definitely have used others (in other builds) from this same batch I got from Mouser, but it’s worth a try. I’ll let you know.

Does changing the position of the 3 toggles around effect the Footswitch Pop!???

 

[Kroars]

Yeah, the others I built all had 10R there with no issue.

Does changing the position of the 3 toggles around effect the Footswitch Pop!???

It does. The Harmonics and Bright make it a lot worse. The other, not nearly as bad, if any difference. Although, it does it when all three toggles are removed as well.