Conductive paint ground loop?

sporks

New member
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9
I apologize if this information is available elsewhere and i missed it...

If i paint the control cavity with conductive paint, and it comes in contact with the jack (which is the ground)... will this introduce a ground loop since other components (pots, switches, etc) are touching the conductive paint?

I imagine it would... So should I take great care to ensure the ground terminal on the jack is NOT touching the conductive paint? And do i also have to be careful that the metal threaded end (which goes through the body's face) does not touch the paint as well?

Any experience/advice/etc would be greatly appreciated.

Thanks a lot.
- mark
 

line6man

Senior member
Messages
6,443
sporks said:
I apologize if this information is available elsewhere and i missed it...

If i paint the control cavity with conductive paint, and it comes in contact with the jack (which is the ground)... will this introduce a ground loop since other components (pots, switches, etc) are touching the conductive paint?

I imagine it would... So should I take great care to ensure the ground terminal on the jack is NOT touching the conductive paint? And do i also have to be careful that the metal threaded end (which goes through the body's face) does not touch the paint as well?

Any experience/advice/etc would be greatly appreciated.

Thanks a lot.
- mark

I have said this sentence a million times now...
YOU CANNOT GET GROUND LOOPS IN AN INSTRUMENT WITH ONLY ONE GROUND!
A guitar has only one ground point which is at the output jack.
The ground loop in the instrument is so insignificant that it will never cause any issues.
 

sporks

New member
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9
line6man said:
YOU CANNOT GET GROUND LOOPS IN AN INSTRUMENT WITH ONLY ONE GROUND!
A guitar has only one ground point which is at the output jack.
The ground loop in the instrument is so insignificant that it will never cause any issues.

Well... you can, in fact have ground loops.  The fact that there is one ground is irrelevant.  I don't think there's any disputing that.

Now the question of how significantly ground loops affect the sound quality is another matter. I'll take your experience (that they're insignificant) in consideration. Thanks.

But I still think it's prudent to avoid them if possible. It certainly can't hurt. So if anyone has any advice/input regarding my question (as to the logistics of preventing it with a painted cavity), i'd be interested to hear.
Thanks again.
 

line6man

Senior member
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6,443
Well, one tip i have for you is not to ground any components thru the shielding only. Always make sure that components have a direct path to ground, because that paint really isn't all that conductive. I have seen people get readings of as much as 2 ohms going from pickup cavity to pickup cavity.
 

Funky Phil

Senior member
Messages
324
Conductive paint has some resistance, so it's probably not the best ground...
If you use foil screening, then that would make more sense...

BUT, In my experience, shielding doesn't make that much difference anyway.
(Let's not start a thread about "to shield or not to shield"...it's been done many times before I think!)
 

dbw

Senior member
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4,531
I have 2 guitars with the pickups grounded only via conductive foil.  I measure the resistance at 0 ohms.
 

mayfly

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8,299
To help muddy the waters a bit more,

You might have two paths to ground from that output jack - one from the wire and one from the paint.  Technically this is a ground loop.

However

The only time a ground loop becomes a problem is if there is significant voltage difference between the two ground points.  If this is the case, then current starts to flow in your grounds.  It's the current that causes the audible noise.

How do you get this current?  Two things have to be in place:  you have to have one ground path that has a bit of resistance to it.  The paint would qualify.  The second is that you need to be dumping quite a bit of current through that path.  Like the negative lead in a power supply decoupling capacitor in a 100W tube amp for example. 

You are not pushing that kind of current in your guitar (esp if it's passive), so you can't end up with two ground points that are at different voltages. So, even if you have a ground loop, you won't get any noise.  Well, noise caused by that anyway.

Hope that helps and not makes it more opaque. 
 

line6man

Senior member
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6,443
dbw said:
I have 2 guitars with the pickups grounded only via conductive foil.  I measure the resistance at 0 ohms.

Conductive foil is fine. Conductive paint on the other hand is quite resistive. I always suggest that people should use the foil for shielding because it works better than paint.
 

sporks

New member
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9
In case it wasn't very clear, I just want to point out that I'm *not* trying to use the paint as a ground connection.  I think a few people got the wrong idea here.

I was trying to prevent a ground loop by ensuring the paint does NOT provide another path to the jack.

Mayfly, thanks for the info. Lol, yes you did muddy the waters of my mind.  I understand the currents are low, and the chances of noise are minimal. But I'm not sure I understand why you say i might actually *want* a ground loop.
The paint will definitely offer more resistance than my desired grounding path (a wire). So that's going to create some weird signals, i think.

I think (unless convinced otherwise) I'll go back to my original plan to simply tape up the jack leads, and scrape the paint away from the front of the jack. But otherwise I won't worry about it too much. Thanks to everyone for your input.
 

mayfly

Senior member
Messages
8,299
sporks said:
Mayfly, thanks for the info. Lol, yes you did muddy the waters of my mind.  I understand the currents are low, and the chances of noise are minimal. But I'm not sure I understand why you say i might actually *want* a ground loop.
The paint will definitely offer more resistance than my desired grounding path (a wire). So that's going to create some weird signals, i think.

Sorry if I was confusing. You don't want a ground loop under any conditions.
 

sporks

New member
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9
mayfly said:
Sorry if I was confusing. You don't want a ground loop under any conditions.

Whoops, no you weren't confusing. I just didn't read the first part of your reply correctly (for some reason I had it in my mind that you said I "might want" one). Hah, It's too early for me.
Thanks again.
 

Keyser Soze

Senior member
Messages
206
The shield needs to be connected to ground somewhere, otherwise it's not really a shield, more like a really poor reflector/antennae.  If nowhere else then grounding at the output jack is fine.

If you want to be 110% sure that there are no ground loops do not use the pot cases for grounding purposes - run all other grounds to a star and then connect the star to the ground lug of  the jack.

Personally I do not like shielding paint.  Copper foil is so much easier to work with (as long as you don't mind the occasional bleeding flesh wound.)
 

sporks

New member
Messages
9
Yea, the shield needs to be grounded.

Again... i think there's a lot of confusion here. Please read the original post.

The question was about inadvertently creating a ground loop due to multiple paths to the ground. For example:
1) volume pot -> ring connector -> jack
2) conductive paint -> ring connector -> jack
3) (inadvertent, introducing ground-loop): volume pot -> touching the paint (which is also connected to the ground via #2)

#3 is therefore a ground loop.
 

dbw

Senior member
Messages
4,531
Incidentally, anyone try these? They look kinda cool, aluminum shield that fits under a strat guard:

http://store.guitarfetish.com/alstpishunsc.html
yhst-50206111187217_2063_18278676
 

blue313

Senior member
Messages
2,824
Nope, but I like these.  It fixed my static issues on my Strat.  I got the Tele one recently, I'm hoping it'll help with that one too.

http://www.monteallums.com/shielding_supplies.html#pickguard

SSS_Copper_s.jpg
 
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