volume/tone pot grounding

J.P. · #1 03-07-2008, 07:38 AM

Hello,

I shielded/grounded my Jazz bass pretty much using Lyle Caldwell's thread and everything came out great.

I moved on to my Rickenbacker 4003. Got everything shielded including the back of the pickguard. I wanted to change the ohms on the pots, so I got all new pots. All the "hot wires/caps" are hooked up. Just thinking through the grounding.

I have read about using the shielding on the pickguard to ground the pots to (no wires, just the pot housing touching the shielding). I like this idea, but:

If I have a lug on the pot that I need to go to ground, wouldn't I need to solder this lug to the pot casing for it to ground to the shielding?
Or am I missing something?

Thanks for any advise.

Also, where is the best place, really, for grounds to terminate? I put a ground lug in my Jazz with everything going there. And I planned on doing the same on the Ric, but I have read elsewhere that the best place for grounds to terminate is the output jack. So, which one is it?

Thanks again

i_got_a_mohawk · #2 03-07-2008, 07:54 AM

Yeah, you need to ground the lug to the casing. Just bend it back and solder it

joeyl · #3 03-07-2008, 08:11 AM

no, you need to keep signal grounds and shield grounds separate, so no bending back the tab to solder to the back of the pot, that would mix it up. run a wire from that lug to the common ground that goes out to the output jack,

notice that in Lyle's pic, no soldering is done to the pot casing, you have to apply the same principle to the Ric wiring

i_got_a_mohawk · #4 03-07-2008, 08:25 AM

Ive done it both ways, never had any additional noise or other issues through either.

joeyl · #5 03-07-2008, 08:31 AM

true, but I never liked soldering to the back of the pots anyway

I think it takes too much heat to get a clean enough solder joint using rosin core solder, and if you use flux, too much will cause the joint to corrode because of moisture (but that part may be because I live in the swamp state)

i_got_a_mohawk · #6 03-07-2008, 08:41 AM

I dare say thats true, your less likely to use too much heat and bugger up the pot!

J.P. · #7 03-07-2008, 10:39 AM

O.K. Thanks for the info guys.

So, I hooked everything up like the jazz (sort of). I have the pickups (negative) and the bridge going to a lug in the cavity. All the other grounds from volume/tone pots go to the output jack.

No soldering to pot casings. (I live in Lake Charles, Louisiana by the way--so I know about humidity!!)

I plugged into amp and got some pretty good hum (not the good kind). I opened the guitar back up while still plugged in and started looking around. Everything looked right (I could very well be missing something though).

I grabbed a jumper wire and just for the hell of it connected one end to the lug in the cavity and the other end to the ground on the output jack. Hum gone. Everything works well and is quiet. I can run a wire from the lug to output jack, no problem. I just don't understand why this gets rid of the hum.

Is it because: on the Jazz, although I didn't run a wire from lug to output jack, the output jack is physically against the metal control plate, which is in contact with the shielding and lug?

Can someone explain.

Thanks

joeyl · #8 03-07-2008, 03:04 PM

Quote:

Originally Posted by J.P.

Is it because: on the Jazz, although I didn't run a wire from lug to output jack, the output jack is physically against the metal control plate, which is in contact with the shielding and lug?

Can someone explain.

Thanks

that sounds about right. I always put a connection between lug and output jack also

DavidRavenMoon · #9 03-07-2008, 05:17 PM

Quote:

Originally Posted by J.P.

I grabbed a jumper wire and just for the hell of it connected one end to the lug in the cavity and the other end to the ground on the output jack. Hum gone. Everything works well and is quiet. I can run a wire from the lug to output jack, no problem. I just don't understand why this gets rid of the hum.

Is it because: on the Jazz, although I didn't run a wire from lug to output jack, the output jack is physically against the metal control plate, which is in contact with the shielding and lug?

Yes, that's the reason. You didn't have a valid ground connection on the Ric.

There's nothing at all wrong with soldering the grounds to the back of the pots. You will NOT get a ground loop. That's a myth. Ground loops come from two pieces of AC powered gear being plugged into two different grounded outlets, and then looped together by a patch cord.

You can't get a ground loop in a bass because there is only ONE ground.. the one that goes to the amp. The amp is the ground source.

The only problem with having the ground made from where the pots or jack connect to foil, or even a metal plate, is you run the risk of the foil having higher resistance than a piece of wire would, and also if the pots or jack come loose, you will lose your ground connection!

Look at the way EMG supply their prewired Strat controls. They have a solid piece of wire (bus wire) soldered across the back of each pot.

Think of it this way, look at an effects box. You have all the pots, switches and jacks connected to the same aluminum or steel box, so the back of the pots and the foil are just forming a shielded enclosure.

So all the shields in a bass should be connected together, and then run them to the main ground.

Here's a good illustrated how to:

MIMF.COM Bill Machrone's photo essay: Installing new pickups [Pictures]

joeyl · #10 03-07-2008, 05:32 PM

I reject your reality and substitute my own (mythbusters)

here is what I use, back in 1996 or 1997, Lane Poor sent me this. No risk of sound cutting off due to loose pots, the pot casings are merely little shields connected to the big shield of the cavity..

DavidRavenMoon · #11 03-08-2008, 03:43 AM

Quote:

Originally Posted by joeyl

the pot casings are merely little shields connected to the big shield of the cavity..

Yes, they are... but how is the cavity shield getting grounded?

The thing about bending the lug and soldering it... it's done because A) it doesn't require an extra piece of wire, and B) it's the shortest connection to ground.

If your soldering skills are not up to par, you might get a bad solder joint there, but that's the only issue with doing that.

It's been done for an awful long time with no problems.

I keep all my shield grounds separate from the pickups too, but as soon as you are at the controls, that separation is over. You only have one ground, which is at the jack. There wont be any advantage to having two wires, each a few inches long, compared to one going to the jack.

J.P. · #12 03-08-2008, 01:53 PM

Thanks guys for all the info. I really appreciate it.

All's well with the Ric. Sounds good and really quiet (electronically wise).

Here's one more question I have thought about though if someone feels like answering.

If you have, say, four pots that you need to ground, does it make any difference if you: a) run a wire from each individual pot to ground (the way I did it)or b)if you daisy chain them?

Is one supposed to really be better than the other, or does it matter? Just curious.

Thanks

DavidRavenMoon · #13 03-08-2008, 02:47 PM

Quote:

Originally Posted by J.P.

All's well with the Ric. Sounds good and really quiet (electronically wise).

Did you actually have a noise problem with the Ric? I always found my two '73 Rics to be pretty quiet, especially considering they have single coil pickups. I think the key is they use shielded wires.

Quote:

Originally Posted by J.P.

If you have, say, four pots that you need to ground, does it make any difference if you: a) run a wire from each individual pot to ground (the way I did it)or b)if you daisy chain them?

I would daisychain them, and then run the ground from the pots/switches/shields to the jack's ground separate from the signal, i.e., from the pot's terminals.

But I'd wager if you tried it both ways, as well as the way the Ric was wired stock, you wouldn't hear a difference.

Quote:

Originally Posted by J.P.

Is one supposed to really be better than the other, or does it matter? Just curious.

Some people seem to think so. I think the real reason is they start off with a noise unshielded guitar like a Strat or Jazz bass. They have minimal shielding, and don't use coax cable from the pickups or pots. Then they do all the mods at once, and attribute any improvement to everything they did, when it might just be the added shielding.

Anything you do in this case should be an improvement. Just replacing the unshielded wire to the jack should make a difference. But just redoing your grounds to a star ground layout, while not shielding the bass wont make it quieter, unless it had bad grounds to start with.

I have a few basses and guitars I made with minimal shielding... just some foil under the pots, but they have well shielded hum canceling pickups, and coax cable, and they are dead quiet.

I had one of my Rics completely shielded with copper foil, two humbuckers (a Gibson sidewidner and Bartolini Hi-A) and no string ground. That was the quietest bass I owned.