EQD Disaster Transport Junior - popping when stomp switch engaged

[Philtre]

Hi, I've built and boxed up the EQD Disaster Transport Junior:

http://tagboardeffects.blogspot.co.uk/2017/12/earthquaker-disaster-transport-jr.html

The offboard wiring is as here - http://tagboardeffects.blogspot.co.uk/2012/02/offboard-wiring.html

Problem:

Works fine except for a loud pop when the stomp switch is pressed on and off. Also, when on, it causes any other pedals between it and the amp to have a pop when pressing their stop switches.

Analysis:

There is a 1M resistor between input and ground in the circuit. I tried adding another 1M resistor between output and ground but made no difference. Also tried disconnecting the LED in case that might affect it, again no difference.

Update - I measured DC voltage at the output. There is about 1.3v DC between output and ground.

Anything else I can try?

[induction]

The output cap on that layout is backward. That could easily cause your problem. I'd replace it rather than just reversing it, as it may be damaged by now.

P.S. Since you used the standard offboard wiring, I'm assuming you used the non-tails layout. Is that correct?

Philtre wrote

I tried adding another 1M resistor between output and ground but made no difference.

Just wanted to point out that there is already a 100k pulldown on the output.

[Philtre]

induction wrote

The output cap on that layout is backward. That could easily cause your problem. I'd replace it rather than just reversing it, as it may be damaged by now.

P.S. Since you used the standard offboard wiring, I'm assuming you used the non-tails layout. Is that correct?

Yes, non tails version.

You mean the 1uF cap top-right should have the negative side connected to the output?

[induction]

Philtre wrote

You mean the 1uF cap top-right should have the negative side connected to the output?

Exactly.

[Philtre]

I swapped the cap out and put it the right way and it works perfectly now.

Thanks very much for that, induction.  :-)

[induction]

My pleasure. Glad you got it working.

[Philtre]

Yeah, it was a perfect outcome. I was ready to ditch the pedal.

And, BTW, it looks like the layout has been updated already. https://tagboardeffects.blogspot.co.uk/2017/12/earthquaker-disaster-transport-jr.html?showComment=1522183301433#c2362691832189533748

Result! :-)

[Philtre]

I'm trying to understand the theory behind this. I know that a capacitor placed in series will block DC and allow AC to pass. But why was the AC and DC passing through the cap when the polarity was reversed?

[induction]

Electrolytic caps block DC only when polarized correctly. They act like caps in one direction and jumpers in the other direction. As DC current runs through a reversed electrolytic, it heats and destroys the dielectric material inside the cap, until the cap eventually fails (turns into a jumper in both directions) or even explodes.

[Philtre]

induction wrote

...or even explodes.

Now that would be an EQD Disaster!