Grounding Pot Bodies

[Paul Marossy]

I know it is convention is that you solder your grounds to the back of the pots and connect all grounds together. But, couldn't one just do a ground bus instead? Is there any advantage to having the pot bodies themselves grounded? Is it mandatory for safety? Even so, I don't think it is a big thing since the knobs are plastic. Am I right or am I wrong in my thinking?

[Dugz Ink]

In my opinion, the method that kills the most noise is to run two seperate ground "circuits" that eventually go to the same ground point. Circuit #1 would include (but be limited to) all of the pickup wires that will be sent to "ground" and all of the pot/switch terminals that will be sent to "ground". Circuit #2 would include (but be limited to) all shielding (including pot/switch bodies) and the bridge. Both circuits would meet and terminate at the ground lug on the output jack.

This method helps to keep the things that pick up RFI from transmitting said RFI to the ground terminals in your audio chain as said RFI is going to the ground lug. Instead, the RFI travels a parallel path that does not have direct contact to the audio chain's ground until it gets to the ground lug... which is where you're bleeding off the RFI. (Unless your guitar cable is hooked to a bad ground... then everything is screwed.)

Some switches will have terminals that are connected to the switch cover/casing. In a case like that, you should avoid connecting the terminal to one circuit and the body to the other circuit. First, that introduces the RFI into the audio chain before it gets to the ground lug. Second, if there is any measureable resistance in one of the ground circuits (but not the other) it will create a ground-loop hum.

With all of that said, you CAN ground everything to everything on something as simple/small as a guitar and get away with it... most of the time. Especially if 1) you're not in an RFI-rich environment, and 2) you have really good connections.

But there are people who will argue to the death that there is ONLY one way to do it.

I'm not one of them. I've seen too many things that defied the laws of science.

D~s

[Paul Marossy]

I personally don't see anything wrong with your suggestions. So, the reason for grounding the pot bodies I take it has more to do with preventing problems with RFI / EMI than with safety?

[lovekraft]

At the signal levels we're using, there's probably not going to be any audible difference between a textbook star-ground setup and a buss system, or any other logical layout for that matter. Just do whatever you do in your amp chassis. The problems I see are usually caused by the belief that "ground" is at the same potential in all places, f'rinstance when everything is grounded to the copper foil of the shielding, but at different places, often with joints in between, or when there are multiple paths to ground from components, usually one wire and the shield. So long as you pick a single ground point (or buss) and route everything to it, you shouldn't have any problems. And you ground the pot bodies just to help shield everything, just like in an amp.

The only thing I've ever seen that defied the laws of science is the audience at the John Edwards Show.

[Paul Marossy]

So long as you pick a single ground point (or buss) and route everything to it, you shouldn't have any problems. And you ground the pot bodies just to help shield everything, just like in an amp.

I was just applying my experience with building three tube amps here with my original question. I was thinking that a ground buss would work fine, I just wasn't sure about the pot bodies, though. Now I think I get the idea behind the reasons why guitars are grounded the way that they are. Thanks!

[Dugz Ink]

So, the reason for grounding the pot bodies I take it has more to do with preventing problems with RFI / EMI than with safety?

The "shield" is exactly that; it shields the low-level signal from outside interference.

The metal body of a pot can do the same thing, if grounded properly.

Of course, if it's not grounded at all, it will basically absorb the RFI, which puts the low-level signal in an RFI hot-spot. That leads to things like picking up bad AM radio stations on your guitar... or a ton of "buzz" (EMI) from a computer's CRT video monitor while youre trying to record some new licks on your computer.

D~s

[Paul Marossy]

Of course, if it's not grounded at all, it will basically absorb the RFI, which puts the low-level signal in an RFI hot-spot. That leads to things like picking up bad AM radio stations on your guitar... or a ton of "buzz" (EMI) from a computer's CRT video monitor while youre trying to record some new licks on your computer.

Hmmm... I wonder if that is what the problem is with a bass that I own. I'm going to have to check that out!!