Possible grounding problem

[KarenColumbo]

Hi, guys,
Just finished a little side project with am opamp clean booster (http://www.jer00n.nl/2010/07/28/clean-boost-for-guitar-or-bass/. So far it works fine, when it's not in its enclosure. When I put everything into the hammond box and connect it I get extreme sharp and loud pops when I touch the case with my finger and ground loop noises.

As you can see (at least I hope so), I use isolated plastic jacks, an isolated DC jack and a neoprene LED-socket. Only part directly connected to the chassis are the shaft of the 3pdt switch (although it is isolated with plastic washers top and bottom of the shaft) and the pot shaft respectively the housing (haven't any plastic washers left).

The board is affixed via double sided thick foam pad. No connection there.

How do I ground the whole thing so it doesn't kill my amp?

I wired everything according to plan - still it doesn't really work

[KarenColumbo]

[KarenColumbo]

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[EBK]

Some people will tell you to solder a ground wire to the back of the pot (I'm not one of those people).

If you are going to use isolated jacks, then I'd suggest adding a ground wire via a ring terminal  around the pot bushing, essentially acting like a washer.

I think you are overisolating, but I dont consider myself a grounding/shielding expert.

In my builds, the DC jack (plastic) and the input jack (via fiber shoulder washers) are all that are isolated.

[KarenColumbo]

Thank you for the answer. Only: What is a pot bushing? Couldn't find anything about that

You mean I could take the violet wire from the output jack (which is a ground wire), unplug it from the board (since it is connected to ground via several other wires) and put it on the pot housing?

[EBK]

The bushing is the threaded part of the pot that goes through the enclosure.

[EBK]

If your output jack is isolated, you can't disconnect its ground wire.  You could add another wire from there if you want, and connect that to the pot.

Your input jack is grounded too, right?

[KarenColumbo]

This, Sir, did the trick. Thank you VERY much! 

[KarenColumbo]

If your output jack is isolated, you can't disconnect its ground wire.  You could add another wire from there if you want, and connect that to the pot.

Your input jack is grounded too, right?

Yes, there is a ground wire leading from the input jack to the PDT board and from there to the respective ground pad on the board.

[digi2t]

That's why I'm not a big fan of isolated jacks, unless the circuit has some contingency at some point of transferring ground to the chassis. The open style jacks are fine for that, since the ground lug usually crimped with the bushing. Some folks will go as far as not using a wire between two open jack ground lugs, allowing for the enclosure to shunt ground between them. I always found this to be a bit chancy, especially if the jack nuts get loose over time, so I tend to add the wire.

[KarenColumbo]

I see now. Well, next order will be open type jacks, that's for sure.

[PRR]

The case "MUST" be connected to circuit ground. Otherwise it *attracts* crap, instead of catching and diverting crap.

If you really isolated EVERYthing, then put a screw in the case and jumper it to circuit common/ground.

Laying a short bare ground wire in the crack while you screw the lid on may be a low-class alternative.

Soldering to a all-metal pot body, or a pot bushing lug (they exist) will work. But pot bodies don't solder well.

Using at least one metal-bushing jack works very well without any added effort.

Multiple case grounds invites trouble in large systems, but seems benign in stomp-size boxes.

[blackieNYC]

you can stick with those jacks though, since you own some.  It might be tricky finding "ring terminals" that fit a pot shaft. shop for one for a bolt size of the shaft - what it that? 3/8
this would be a pretty good ground:

[EBK]

Here's the ones I have used before:

Allstar Performance ALL76006
3/8" Hole Ring Terminals Non-Insulated
Spec'd for 22-18 gauge wire.  It's hard to find a large ring terminal for small wire.

[blackieNYC]

If you bend EBK's along the center of the loop, it becomes a spring-like lockwasher, keeping pressure on the tightened-down pot, switch, jack. Hard to splain.

[EBK]

If you bend EBK's along the center of the loop, it becomes a spring-like lockwasher, keeping pressure on the tightened-down pot, switch, jack. Hard to splain.

Great idea!

[pinkjimiphoton]

always ground your casing to your star ground point if possible. or like paul says, it becomes an antennae.

i'd say always ground your pot casings too, if not in a metal enclosure. sometimes if ya "rock it before ya box it" and the pot casings aren't grounded, it can squeal like a pig (i had that issue with gus's octave up sick box until i grounded the pot cases... it was fine in the box, but testing it drove me thru all kindsa hoops)