Grounding Problem?

[KerryF]

Ok, so I built a pedal for someone and it worked great and all.  I shipped it to him and he recieved it.  Well, when he plugged into it to play, he said there was a lot of interference.  Well, I did use a plastic box and all.  But he said that when he touches the nut on the jack holding the jack on the box, the interference goes away, and the fuzz works.  I thought maybe it was because of the box not being grounded (here it doesnt need to be grounded, we dont get interference).  So I told him to connect a wire to the outside of the jack and touch it to the ground to see if that would act as the box being grounded.  He did it and it still didnt work, but when he touches the end of the wire, the interference goes away again.  He says it works fine when bypassed, so im not quite sure.

If anyone can give me maybe an idea of what the problem could be, that would be great.

Thanks. 

[Gilles C]

Did you connect all the jacks (Input and Output) body together in your box?

And what jack does he touch to make the hum go away? Input or Output?

I had the same problem last week when I tried a circuit I mounted on a metal front plate. It was powered by an isolated 9Vdc (spyder style). None of the jacks or pots were connected to the plate. The metal plate was floating. And when I was touching the plate, I was hearing hum. I had to connect the metal plate to the ground.

Being in a plastic box, a ground connection could  be missing. It could do the same while touching the pots. The metal body of these parts are acting as antennas when not connected to ground.

Gilles

[Gilles C]

Double post...

[KerryF]

Hmmm... So how can I solve this for him?  I have no metal plates on the bottom of it.  Everything is connected fine because it worked fine for me before I shipped it.

[KerryF]

ok, so i went through some debugging inside the pedal (made sure nothing was touching, everything was connected, etc.).  well i got him to take a wire and connect the input jack and output jack together (they are connected on the board).  he said that this took away some of the buzz and allowed him to hear the actual fuzz pedal which he says does sound great.  i am wondering, I got him to get some buzz away by connecting the jacks like that.  what else can he do to maybe make less buzz?  Maybe also connect that wire to the jack's grounds?  but that doesnt really make much sense .  so what else can he do?

thanks

[GibsonGM]

With a plastic box, since it's non-conductive, you might try removing all the components from the box.  Line the box with aluminum foil, using a spray contact adhesive or whatever.  Pop holes for pots & jacks.  Replace all the components.   Run a ground from the input jack ground point to board.   Output jack gets grounded to the board, too, at the same location (star grounding, all grounds to same place).   When you install the jacks, the body of the input jack then connects the foil to ground.   
Make sure the bottom of the box has the foil, too, and that it will positively contact the foil in the rest of the box when it's closed up.   This prevents RF interference, a likely source of your problem   OR, use a metal box 

When you've got the stuff out in the open, re-check the pots etc. for good ground contact, another source of noise. 

Hope this helps!

[KerryF]

Well, the guy has this pedal, and its not radio frequencies because when he touiches the jack on the outside, the buzz stops.  So I dont think it has to do with that.  That parts are fine and all.  He says it sound great when he is touching the jack and the buzz stops.

[Gilles C]

I also would have suggested to add some shielding, but the fact that it's not available makes things a bit (lot...) more difficult.

The fact that it worked well before shipping could mean that a wire got loose, or something is not as shielded in this guy's stuff, or that the wiring of his home is generating more hum than yours.

I know that the wires in my room makes it a good place to test for hum... It could be the same that guy, and you may have a clean (hum free) room.

I'm affraid of telling the crazy things I would try myself  Like wrapping the box in aluminium paper with the ground touching the alum paper. It would tell if it needs more shielding. Then, I would keep working on the grounds with a wire. Not easy to work from a distance.

Gilles

[GibsonGM]

Exactly, Gilles is on the right track....problems may come back if the guy uses the pedal in a different location, etc.  Maybe he should just mail it back, and you can do the mods on it.  I like the idea of wrapping the whole thing in aluminum foil on the OUTSIDE temporarily, connected to board ground or batt -9v, just for testing.

I do seriously suspect that the output jack needs to be connected to ground, something has come loose or twisted, if the buzz stops when touching it.   Ask him to try different cables, too, maybe....or the jack might be defective, etc etc.  Easiest to fix if you can get at rather than him!   If the wire between in & out does something, start there....yes, they should both go to ground - and MUST, if the box is plastic and the output isn't grounded!   
Is this a positive ground fuzz pedal?  I've read about buzz with the negative conversions for the PNP circuits...

[MetalUpYerEye]

Could be his set-up. I know that when my friends plug their guitars into my set-up it sounds like a thrashing machine rather than musical sound.

+1 for him shipping the pedal back so you can look at it. After all you built it, not him.   

[KerryF]

ok guys, so the problem with taking it back to fix is that I dont have any buzz or frequency feedback here.  so it will be hard to fix it if i cant hear it and test it for myself.

this is positive ground (PNP).

Its cant be his setup (at least not the amp Vox AC30).  I will ask about cables but he says it works when bypassed fine.  I will look at the schematic again to see whatesle i can think of.