Pedal pops even with a pulldown resistor

[kraigen]

Hello, all!
I built an OCD today and my pedal produces a loud pop when engaged, even though I am using a 1M pulldown resistor, as stated in the pcb I'm basing my pedal on.
http://effectslayouts.blogspot.mx/2016/06/fulltone-ocd.html

[Kipper4]

Use your meter to check for DC at the input and output.
popping can be a sign theres some dc voltage at the input / output.

Tell us about your signal chain? Is there some dc coming from the amp?
Are there other pedals in the chain?
Which switching did you use?
a picture can paint a thousand words....

[anotherjim]

Popping can also happen on the output - you have fitted the volume control? That acts as the output antipop pulldown. You can also get a pop if the next thing the pedal drives doesn't have anti-pop or is leaking DC.

I see no provision for an indicator LED. If done wrong, the LED current can be excessive and generate a pop in the circuit by making the 9v supply dip or capacitively coupling to the signal wires in a 3PDT bypass switch.

[GiovannyS10]

I already had a problem like this, i used pulldown, ground in, led resistor, voltage divider, capacitor, and nothing worked. I solved it groundening the board out on 3PDT.

Like in the image below:

[R.G.]

1M pulldown resistors are not magic amulets protecting you from pops. They do one thing - they pull the leakage of input and output capacitors down to too low a DC voltage to be a significant pop.

In particular, they do not make up for things like mis-wiring or particularly, incorrect orientation of electrolytic caps on the input or output. They can't pull enough current to ground to make up for the huge leakage of a reversed electro.

There are also many other ways to get pop that don't respond to the 1M. As noted, check the input and output of the PCB for DC from other causes, too.

Check that and report it back here.

[kraigen]

Popping can also happen on the output - you have fitted the volume control? That acts as the output antipop pulldown. You can also get a pop if the next thing the pedal drives doesn't have anti-pop or is leaking DC.

I see no provision for an indicator LED. If done wrong, the LED current can be excessive and generate a pop in the circuit by making the 9v supply dip or capacitively coupling to the signal wires in a 3PDT bypass switch.

I used a 1k resistor for my LED, and it was wired this way. I've used this configuration with success before.

[GGBB]

If you want to determine whether its an LED problem or not, disconnect the LED (or - probably easier - jumper it always on).

[JerS]

Double check the orientation of the 2.2Uf electro cap on the output of the pedal. If reversed, it could cause the pop. Also check for a small short across the pins of the same electro cap. A short here could also cause the volume issue you are having.

Cheers - Jer

[kraigen]

Double check the orientation of the 2.2Uf electro cap on the output of the pedal. If reversed, it could cause the pop. Also check for a small short across the pins of the same electro cap. A short here could also cause the volume issue you are having.

Cheers - Jer

I've checked all the electro caps and their orientation is correct, there isn't a short in the one you mention either, or any other.

[R.G.]

Third time, I think.

>>> Is there a DC voltage on the input or output of the signal connections in/out of the PCB?? <<<

[kraigen]

Third time, I think.

>>> Is there a DC voltage on the input or output of the signal connections in/out of the PCB?? <<<

Sorry, I forgot to answer this. I measured for DC voltage in both and there was aboout 3 mV.

[anotherjim]

1K LED resistor is actually a touch low value, even for ordinary 20mA LED's. With a modern high brightness LED, you could probably see it from space! I find 6k8 is a good minimum.

If you have fitted a pull-down on the input, the strap wire on the 3pdt that grounds the board input when bypassed, is probably best removed as it is causing a large step change in the input conditions of what can be a very high gain circuit.

I think the in and out coupling capacitors of the OCD are both film types in nF values, which are rarely any problem unless faulty.

[Rixen]

IMHO it is impossible to eliminate all noise from typical true bypass switching. The switch itself generates piezo-electricity from it's materials.

[Plexi]

I had that problem one time.
I found out that was a very very small, a few microns  of welding hair crossing two tracks.

[MrStab]

another possible solution is the 2nd diagram here: http://www.muzique.com/lab/led.htm , though this won't mask any other underlying problems with the setup.