DC on output when bypassed = pop.

[edgar uses tools]

Hey, everyone.

I built a Red Snapper and CAE Boost/Buffer in the same box, both from the layouts over at tagboard effects (such a great site!). I omitted the buffer/boost switch from the CAE side since I can just run the boost pot at minimum if I want a buffer.

http://tagboardeffects.blogspot.com/2012/04/menatone-red-snapper-4-knob.html
http://tagboardeffects.blogspot.com/2014/03/mxr-mc-401.html


The RS works great, and the CAE also works great, but the CAE side is giving me a loud pop. I'm getting readings of about 12.5mv on the pedal's output when the CAE is bypassed and .4mv when it's engaged. My understanding is that a pulldown resistor would help if there's DC present when the pedal is engaged, but I can't figure out how I'm getting DC on the output when both effects are bypassed  :hmmm:

Any thoughts? I'm using footswitch PCBs that ground the effect input when bypassed. I've used the wiring scheme as in the image below, and the footswitches are really just PCB versions of that. I've used them in about a dozen other builds with no problems:


Thanks in advance!

[bloxstompboxes]

Might be a good idea to show us your wiring. If you are measuring the output of the board then it is possible to get a voltage if there is no pulldown resistor regardless if the effect is engaged or not. This is because the board always has power since the guitar plug and jack act as a switch in most wiring configurations. The true bypass switch just determines if you hear the effected signal or the original signal from the guitar. Post a pic of your wiring or at least a diagram of the wiring scheme you're using.

Edit: also, your links are not done properly. They resultant page gives a doesn't exist error when clicking on them. I'm at work right now so can't really dig a whole lot further than that.

[edgar uses tools]

Sorry about the links! I'll fix those and give a rundown of the wiring when I'm at my computer and not on a phone.


I'm getting dc on the output jack of the pedal when both effects are bypassed, which seems strange.

[edgar uses tools]

First post edited with the wiring details and corrected links. Thanks!

[bloxstompboxes]

I don't see a pulldown resistor on either one of those boards. I hate looking at vero/stripboard but here it goes. Try adding a 1Meg or better from each input to GND one effect at a time and then see if the pop is still there. You could also try one on the output of each if one on the input doesn't solve it. The booster has quite a few large caps at the in and out side of the board so that is probably the culprit board if not both. The caps rapidly carging and discharging when stomping on the swithces is what is most likely causing the pop. Start with the booster first.

[nocentelli]

Both veroboards already have a 1 meg pulldown resistor on their respective inputs; the red snapper also has a 250k or less volume pot as a pulldown on the output, and the booster has a 10k resistor to ground on the output cap. Additional pulldowns are unlikely to help.

[induction]

I don't see a pulldown resistor on either one of those boards. I hate looking at vero/stripboard but here it goes. Try adding a 1Meg or better from each input to GND one effect at a time and then see if the pop is still there. You could also try one on the output of each if one on the input doesn't solve it. The booster has quite a few large caps at the in and out side of the board so that is probably the culprit board if not both. The caps rapidly carging and discharging when stomping on the swithces is what is most likely causing the pop. Start with the booster first.

There are 1M input pulldowns on both boards. The CAE has a 10k output pulldown and the Snapper has a 250k volume pot at the output.

Even if there were no pulldowns, it wouldn't explain why there is DC offset at the output jack in bypass. It has to be something else. It could be a bad stomp switch, or the DC could be coming from something else in the chain.

OP: When you made your measurements was anything else connected before or after the pedal? Other pedals/amp/guitar?

Edit: Sneaky ninja Nocentelli.

[edgar uses tools]

Thanks for the replies! Induction: the popping is present with other pedals in the chain and also without them. I took the measurements without anything plugged into either the input or output.

[induction]

Have you tried replacing the footswitch and/or its pcb?

[bloxstompboxes]

I don't see a pulldown resistor on either one of those boards. I hate looking at vero/stripboard but here it goes. Try adding a 1Meg or better from each input to GND one effect at a time and then see if the pop is still there. You could also try one on the output of each if one on the input doesn't solve it. The booster has quite a few large caps at the in and out side of the board so that is probably the culprit board if not both. The caps rapidly carging and discharging when stomping on the swithces is what is most likely causing the pop. Start with the booster first.

There are 1M input pulldowns on both boards. The CAE has a 10k output pulldown and the Snapper has a 250k volume pot at the output.

Even if there were no pulldowns, it wouldn't explain why there is DC offset at the output jack in bypass. It has to be something else. It could be a bad stomp switch, or the DC could be coming from something else in the chain.

OP: When you made your measurements was anything else connected before or after the pedal? Other pedals/amp/guitar?

Edit: Sneaky ninja Nocentelli.

Told ya I hate vero/stripboard.  This overtime is killing me too. Sorry about that.

[edgar uses tools]

I finally had some time and tried a new footswitch on the boost side of things. No luck--I'm still getting pops...

[antonis]

Maybe it's time for grounding the output also..