Pedal pops just on some amps

[Lino22]

This guy sent me a Power Boost clone that he said had popped. It didn't pop at my place, at least no more than other true bypass pedals. I checked the wiring, and it was wired with the anti-pop true bypass that grounds the input when the pedal is off. The other side was shunted by the volume pot.

I added a LED pop filter from the excellent AMZ web, just to be sure, and if there have been a slight pop somewhere, the pedal was then dead quiet.

I sent it back and the guy then sent me a video of the pedal, and it pops no matter what, and really loud. It was battery fed and connected simply: guitar > pedal > amp. There was a delay in the FX loop to hear the pop better as it repeated.

Do you guys have any idea what may cause this behaviour?

[antonis]

Amp input cap without pull-down resistor, perhaps..??

P.S.
Despite output "grounded" via Volume pot, it should also be grounded when effect bypassed..

[Lino22]

The 3PDT switch was wired the way the pedal input was grounded when bypassed. So any leaked DC was shunted with 0 resistance to the ground. But the pop on his amp was louder when the pedal was turned on.
Do you think it was the amp?

Why should be the effect output grounded when bypassed? The 100k pot must work better than a 1M puldown right?

[antonis]

I mean directly grounded, when bypassed, hence caps instantly discharged..
(no practically RC time constant..)

[Lino22]

Hmm ... but the input cap was directly wired to ground, but the pop was really loud.

[antonis]

But the output cap wasn't directly grounded, was it..??

[Lino22]

No it wasn't. Do you think that may be it? The 100k should shunt the DC to the ground pretty fast, and he took time between the on/off when he presented the pop.

Is there a trick how to wire 3PDT and ground both input and output when bypassed?

[antonis]

[patricks]

Outside thought, but what else does he have connected? Does the pedal pop when it's the only thing in the chain, or is he connecting it within his pedalboard?
My TC Electronic polytune puts some DC on the input of the pedals down the chain from it and I get pops from my true bypass pedals with it in the line, I have to run it in a loop for things to be quiet.

[GibsonGM]

Yes, my thoughts too, Patricks...is the amp input cap leaking DC?   Where is it coming from?
 
Should be able to trace with a meter, IF you have an offending amp available...

[Lino22]

Thank you everybody. I told him to try a different amp and passive pickups (maybe, although i can't see the connection).

He is not able to measure anything

[amptramp]

One thing that is never specified with a 3PDT switch is the order in which the three switch sections transfer contact.  You could have one faster than the other on a batch of switches then another batch will behave differently.  And the order will usually be different for the 'on' and 'off' directions.  This may have nothing to do with your problem, but maybe if you swap switch functions from one pole to another, the problem may be different (I doubt it will be cured).

[Mark Hammer]

Amp input cap without pull-down resistor, perhaps..??

P.S.
Despite output "grounded" via Volume pot, it should also be grounded when effect bypassed..

The basis of pedal ventriloquism.

[Andon]

Is there an output cap on the pedal?

[Lino22]

Yes, 4.7u

[Lino22]

I love this!

[Lino22]

It is the LED. I disconnected it, and the pop is completely gone, even when both my amp and the pedal volume are at max. By the way, i measured 1-5mV leak at the output, but this gets dragged down by the volume, especially when the volume is not all the way up. But the main thing is - the miniature DC leak is not audible.

So the pop is solely a product of the LED current spike that appears on the voltage rail - and here it is - it has the AMZ filter installed. Shall i go for a bigger cap, bigger current restricting resistor, or a different LED? It is a low current LED, no bright.

[GibsonGM]

It's a low current LED?  And it's not bright?  Well, find the proper LEDs to make it the correct brightness and break the 2 resistors into half each.   If original R was 3.3k, for example, try 2x 1.5k resistors...   

I don't know if I would like a 1 to 5mA DC on the output....faulty output cap most likely...will it get worse over time?  Will make the volume scratchy.

[Lino22]

I went for a bigger cap on the AMZ filter 10u -> 47u and the pop is audibly quieter. The resistor split is a good idea, thanks.
Sorry, i mean mV, not mA ))). Elyte caps leak, and yes, they get worse over time when under voltage. I wanted to say that i use low current LEDs, they are not that bright. I don't like the bright ones. Also - less current flow, less pop prone. Well, the power boost has a lot of gain, so that's why the pop gets so loud. I think.

[GibsonGM]

I was wondering where 'mA' came from   I would say a few mV is just normal leakage, it is ok.

You say you run your LEDs at low current...that is good.  High resistance. Modern LEDs are pretty much 'high efficiency', so when an old schematic calls for 390R, we usually need to increase that MUCH (3.9k, 4.7k and higher!)   Adjust the 'anti pop network' accordingly. 

You are correct - the more the circuit is amplifying, the more ANY noise is amplified.