Howling/Whining After Transplant Surgery... Digital Expert's Advice Needed!!

Paul Marossy · April 17, 2007, 10:05:23 AM

This is kind of a weird one that I don't know the answer to, so I am asking it here in the hopes that I can figure this out.

This guy I know decided to take the circuit board out of his Zoom G2 (small digital gutar FX unit) and put it into an aluminum enclosure. He likes this one setting and he never has to change it, so he's OK with having it in a box and not being able to tweak it. OK, so, here's the problem: After the "

transplant surgery", about 15 seconds after power up, it starts to howl and whine up to the point where it's louder than the guitar signal itself, which renders it unusable in its current state. He tried to put it back into the original Zoom enclosure, and it's still doing the same thing. So, apparently it's oscillating, but why?!

Any ideas? He would like me to fix it for him, but I am not sure where to start on this one. I don't actually have it in hand - yet.

EDIT: Here's a picture of it. I'm guessing something is supposed to be grounded, but isn't.
EDIT #2: All of the offboard switches and knobs are disconnected. That would leave stuff floating with respect to ground, wouldn't it?

db · April 17, 2007, 07:35:43 PM

Is it possible that the program has been corrupted in such a way which causes howl round e.g. regenerating reverb or something along those lines? Is there a factory reset option? I would try that with the unit back in the original enclosure with all controls connected before doing anything else. I can't see why it should be an electrical instability problem unless something has actually been damaged in the conversion process or there is a missing ground connection somewhere.

The whole thing sounds like a crazy idea given that if the preset is lost for any reason, one would presumably have to connect all the controls back up to be able restore it. But each to their own I suppose.

Paul Marossy · April 17, 2007, 08:31:39 PM

Yeah, it is a screwball idea, I know. He apparently did this with the idea that no one will be able to copy his tone by looking at his settings. I would never do this myself.

I have a hunch that his input/output jacks might be connected wrong and/or there is a missing connection to ground somewhere...

casey · April 17, 2007, 08:37:09 PM

dude, i know from experience what the issue is....

my guess is that taking the jacks from the board and mounting them to the enclosure has alot to do with it. when you start mixing analog, especially over the chips as seen, it can get kind of hairy. i had a similar issue one time with a rehouse where i made a digital effect true bypass, when i'd get the UNSHIELDED signal cables near the chips, the effect would go nuts..... he needs to get the cables as far from the chips as possible and at the same time as close to their original spots on the board......

hope this makes sense...

Paul Marossy · April 17, 2007, 09:53:08 PM

Quotemy guess is that taking the jacks from the board and mounting them to the enclosure has alot to do with it. when you start mixing analog, especially over the chips as seen, it can get kind of hairy. i had a similar issue one time with a rehouse where i made a digital effect true bypass, when i'd get the UNSHIELDED signal cables near the chips, the effect would go nuts..... he needs to get the cables as far from the chips as possible and at the same time as close to their original spots on the board......

You might be onto something there. Although, he said that it behaved the same way when he tried putting it back into the original Zoom enclosure. Still, food for thought...

Shepherd · April 17, 2007, 10:11:09 PM

Quote from: Paul Marossy on April 17, 2007, 08:31:39 PM
He apparently did this with the idea that no one will be able to copy his tone by looking at his settings.

This is too much. (Where can I find a paranoid, sweaty emoticon?)

We all know what he should have done is put the knobs on wrong. That way, when it looks like it's only up halfway, in reality it's dimed.

Paul Marossy · April 17, 2007, 10:18:18 PM

Yeah, I know, it's kind of nutty!

O · April 17, 2007, 10:18:55 PM

Paul, the corners look like they were snipped... is it possible that something got snipped that shouldn't have?

David · April 18, 2007, 08:18:03 AM

Quote from: O on April 17, 2007, 10:18:55 PM
Paul, the corners look like they were snipped... is it possible that something got snipped that shouldn't have?

+1

I think O is on to something. The symptoms seem to indicate that something was damaged during the rehouse.

Paul Marossy · April 18, 2007, 08:24:46 AM

Huh, I didn't notice those corners. Could be another source of problems. If the guy ever brings it over, I'll be sure to check it out!

Sir H C · April 18, 2007, 08:59:45 AM

He could have thought that it was a 2 layer PCB, saw that the corners were "safe" and cut to find out that it is more than 2 layers.

Also are all the screws that would have been in it to the original package in there? Often they will use some screws to ground things to the case.

Paul Marossy · April 18, 2007, 09:45:39 AM

QuoteHe could have thought that it was a 2 layer PCB, saw that the corners were "safe" and cut to find out that it is more than 2 layers.

That's a possibility.

QuoteAlso are all the screws that would have been in it to the original package in there? Often they will use some screws to ground things to the case.

Yeah, I'm aware of that. Thing is, I don't know if the case itself is grounded or not. I would assume so...

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Howling/Whining After Transplant Surgery... Digital Expert's Advice Needed!!

db