One pedal pops, one does not. Same schematic

[bramofon]

I've built 2 of the Tonepad Tubescreamer clones and one of them pops when switching, the other does not. I'm trying to find out why but I'm coming to dead ends. I have done several things to try to resolve it. The setup is true-bypass with an LED using a 3PDT footswitch.

- Make sure to pull both the output and input capacitors to ground (output with 100k, input with 2m2)

- remove led from the mix to be sure that's not causing an issue

- Change out footswitch (possibility of a sloppy switch, and I've tried 3 different ones)

The result is that the first pedal is absolutely silent in switching, the other has a pop. I realize all things are not going to be equal and I have checked my connections very thoroughly. The main difference between the 2 pedals is the kind of capacitors used. On the silent switching pedal, some of the capacitors are rated for much higher voltage than necessary. On the noisy switching pedal, the capacitors are from the list of recommended capacitors for such a pedal, including an electrolytic cap on the output. I made a third board and put it in the offending pedalbox (which I've also checked for any possible causes and found nothing). This board has a tantalum output cap. I snapped the board in, and it produces the same pop. I haven't been able to find any other factors that aren't common between the good and the bad pedals.

Any ideas?

[Kipper4]

Same amp , guitar set up?
Did you check for dc voltages on the input and output of the popping pedal?
R G Keens excellant write up on popping pedals is always worth reading.

[kaycee]

Might be a loose ground connection. Try resoldering the wiring connections at all of the grounds, a loose joint on one of those will give you a bang on every switch on.

[bramofon]

It is the same amp, guitar, and 9 volt power supply. I just double checked and the voltage on the ins and outs when switched on and off is zero. I traced all the connections yesterday and was unable to find a loose ground. I'll give it a fresh set of eyes today and see what I can find.

[moosapotamus]

Just guessing... maybe you got a wonky stompswitch?

~ Charlie

[bramofon]

About the switch, I thought so at first too. That would be 3 switches. It is possible, but leaning toward unlikely.

[MrStab]

if the caps are rated differently, then maybe it could be because that different batch also has higher leakage? i'm not knowledgeable enough to know if that's likely to be an issue, just an idea based how you mentioned the caps are the only component difference between that and the other build.

[cloudscapes]

backwards input/output cap? I've done that.

[R O Tiree]

Got any ceramic caps in the one that pops? They can be microphonic.

[bramofon]

Thanks so much for your input guys. It means a lot. I've checked the polarized caps and they are correct. The only ceramic cap is a 51pf. Hold on... there's a difference. I didn't have any 51pf on hand when I made the pop-less pedal. I did have 2 100pf caps that I put in parallel. I will have to check that to see if it's the culprit.

[Jdansti]

About the switch, I thought so at first too. That would be 3 switches. It is possible, but leaning toward unlikely.

Try swapping the switches between the popper and the non-popper and see if the pop follows the switch.

[duck_arse]

I did have 2 100pf caps that I put in parallel.

2 x 100pF in parallel = 200pF, not 50pF. you want them in series for 50pF.

[bramofon]

Ah, you're right. Missed that somehow. I've tried it both ways and seems to make almost no difference in sound.

[zombiwoof]

Did you use the same switch wiring diagram for both pedals?.  I like the TB one that grounds the board input in bypass, and think it helps to avoid popping in some instances.
Al

[amptramp]

If you have a switch with three poles, they do not all make contact at exactly the same time.  One switch may have the input pole faster than the rest, the other may have the output pole faster than the rest and the LED switch contact may also be faster or slower as well.  I really hate true bypass for this reason - production tolerances or unannounced changes may make stompboxes based on these switches behave entirely differently and you will only see the differences with a scope.  And the behaviour when switching on may not correlate with the behaviour when switching off.

[bramofon]

It is a true bypass switching setup up with a 3 pole switch.

What you say makes sense about the poles not lining up with good tolerances. I am after all, only human but I have checked and rechecked so many times, I know my board is good (insert human tolerance for error here). As far as I can see, I've got three bad pedals and one good and I cannot see an electrical difference at any stage. Is there any good way of finding out if it is a "bad" switch? I mean, I've tried three and one that is in use has no pop.

If it turns out to be a true-bypass thing, what switching methods would you suggest? I worked with the millenium switching a bit but just figured I could gain some mileage with a 3 pole. Maybe I just ended up selecting the lazy way out???

[bramofon]

I wonder if maybe I was just being too picky. Maybe the pop isn't really as loud as I think it is.

I remade the whole circuit on a solderless board and hooked up a test switch box. There's still a little bit of pop with the true bypass setup and it seems to be directly dependent on exactly how I press and release the switch. Maybe I'll look into making a high quality buffer and a not-so--true-bypass and see what kind of mileage I can get out of that.