Hearthrob Tremolo DC on output...help??

[sixstringphil]

Just finished Markm's hearthrob using his PCB layout. Sounds great, but I had bad popping on the switch. I've tried pulldowns on input and output, but not much better. When bypassed, I'm getting DC voltage of between 2-3 volts at the output. I've tried reversing and replacing the 4.7uF elec. cap at the output, but still get voltage. Is this normal, or do I have a problem somewhere else? Thanks for the help!!

[John Lyons]

You may have a leaky cap. Even with the pulldowns you get this voltage?

John

[sixstringphil]

That measurement was without the pulldowns and the effect bypassed. With a 1meg pulldown on the output, the popping would gradually go away if I switched several times. I've had pop issues before, but not with that much voltage.

[sixstringphil]

The suspect cap would be the 4.7uF at output? Should it block all DC, or would I expect to see a couple of volts there?

[raulgrell]

It should block pretty much all DC... You'd get some leak, but I wouldn't expect that much...
Try changing caps...

[sixstringphil]

I've tried several of the same cap (and double-checked the polarity). They're the zicon mini electrolytics from Mouser. That's all I have in that value. Should I try another type in a higher/lower value in its place? Also, I tried 1M and 2.2M pulldown resistors, both still pop.

[sixstringphil]

Tried different values of caps, and still getting DC on the output. I checked the voltage at C4 (the last 4.7uF cap) On the positive side, I read 3.05v. On the negative side, (effect output), It starts around 2.7 and slowly drops. Can anyone confirm what the voltage should be before the cap? (My power supply is providing 9.73v) Thanks for all the help so far. This has become extremely frustrating!!

here's a link to markm's layout:
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Hearthrob_Tremolo_LAYOUT.gif.html

[earthtonesaudio]

Have you ruled out a solder bridge?  That signal output trace is awfully close to the 9V supply trace...

Spend a little time looking for careless mistakes, and a lot of times you'll save yourself a lot of time looking for faulty components.

[sixstringphil]

Yes, I noticed how close that particular trace was and made sure that there was no chance of a solder bridge; I even eliminated any flux between the traces. I've also ruled out anything funny in the switch. I'm hooking straight into the jacks and still getting voltage. I'm sure I've missed something carelessly, but I'm not seeing it now.

Just found this thread. Funny, I've been searching all day, and this one just turned up???
http://www.diystompboxes.com/smfforum/index.php?topic=60773.0

[John Lyons]

There may be some voltage on the outside of the cap but really only when the effect is bypassed and without a pulldown resistor.
I would think it to be less than a volt though. The output cap should block all (or almost all) DC from the outgoing signal. That's it's job.

John

[sixstringphil]

Well, I'm going to walk away for a while. I've added 1M pulldowns to both the input and output. That seems to help alot, but the first few switches still pop. I've still got to add the LED tomorrow, so that should really make things interesting!!!