conductive black paint in the control cavity? is this right?

[Snoogles]

i just found out that the black paint inside of the control cavity is conductive.
its a 2 humbucker guitar
the numbers on my multi-meter jump around when i drag the probes across the paint
will this short out connections?
what about the grounding from the bridge to the pots and such?

 

[uOpt]

Re: conductive black paint in the control cavity? is this right?

The conductive paint is usually only used for shielding, not to connect things. If it is solid enough you could use it to connect things, e.g. not solder to the back of the pots (which is stupid anyway).

 

[idsnowdog]

Re: conductive black paint in the control cavity? is this right?

It's graphite paint and it's used for shielding control cavities. Although a poor conductor graphite is an adaquate shielding material and is easy to apply.

 

[Snoogles]

Re: conductive black paint in the control cavity? is this right?

but i'm getting a reading from the multimeter. is that not an issue with the pots and the pickup selector switch?

 

[hermetico]

Re: conductive black paint in the control cavity? is this right?

but i'm getting a reading from the multimeter. is that not an issue with the pots and the pickup selector switch?

What it's usually done is to screw a screw in one of the walls and then, to throw a wire from there to whatever your common ground spot is.
Don't worry about pots and switch. In fact, every pot's case should be grounded, and the switch two.
Just be sure that no hot spot enter in contact with those walls.

 

[constant mesh]

Re: conductive black paint in the control cavity? is this right?

e.g. not solder to the back of the pots (which is stupid anyway).

So, your solution is?

 

[Jason_The_Angry]

Re: conductive black paint in the control cavity? is this right?

I believe the intent was to say that if the conductive paint was thick enough (or conductive enough), the pot's and switch's contact with the paint alone could be sufficient for grounding purposes. However, I would guess the paint is not designed for this, so the electronics are physically wired with grounds. As Hermetico mentioned, as long as you don't have sloppy wiring where the bare "signal" or "hot" wires touch the conductive paint, you should not have issues with shorting, etc.

 

[blueman335]

Re: conductive black paint in the control cavity? is this right?

As Hermetico mentioned, as long as you don't have sloppy wiring where the bare "signal" or "hot" wires touch the conductive paint, you should not have issues with shorting, etc.

+1. If a hot wire or lug touches it, that will sort out the PU. Not an issue with ground wires or lugs, they're all in one big loop.

 

[constant mesh]

Re: conductive black paint in the control cavity? is this right?

I believe the intent was to say that if the conductive paint was thick enough (or conductive enough), the pot's and switch's contact with the paint alone could be sufficient for grounding purposes. However, I would guess the paint is not designed for this, so the electronics are physically wired with grounds. As Hermetico mentioned, as long as you don't have sloppy wiring where the bare "signal" or "hot" wires touch the conductive paint, you should not have issues with shorting, etc.

Well the paint/shielding does serve this exact purpose - to reassure common ground and possibly eliminate any unwanted RF frequencies by Farraday effect. You still have to solder the outer lug of the vol pot and the cap of the tone pot to the ground. Unless you want to have a tab screwed into the body and a bird's nest of wires going there, you still have to ground other wires somehow.
Soldering the pot's housing is less stressful than soldering a single lug. And you can't avoid that last part. The heat dissipates much better over the housing surface, where as with lugs it goes straight to the wafer.

Some people just strive to differentiate opinions on something that worked for decades even before our parents knew about pampers, just because it's posh to think differently.

 

[uOpt]

Re: conductive black paint in the control cavity? is this right?

So, your solution is?

Potentiometers like the ones we use in guitars are not meant to be soldered on the casing.

They are supposed to be grounded by mounting them into a metal plate, such as the front plate of an amp.

This fashion to use the back of the pot as "mass" for the whole guitar and then abuse the player's belly (or in the case of Les Paul players the balls) as shielding has simply been brought up because the original electric guitar manufacturers wanted to save money. And the pickups back in the day were all single coil and hummed like mofos anyway so shielding the cavity would be quite useless microoptimization. From there the fashion stuck because players wanted "vintage like" and manufacturers didn't mind since it's cheaper.

The only attempt to correct this was done by Gibson during some bad times when they had a thick copper shell all through the cavity, with a lid that you would put on. They were grounding the pots via the mount and they removed that life-threatening nonsense of grounding the strings. But the solution was totally overdone and people hated it. I never owned one of those but apparently the copper casing was so large and thick that it resonated mechanically and it had all kinds of unwanted electrical properties.

 

[constant mesh]

Re: conductive black paint in the control cavity? is this right?

Thanks for your opinion, you have a point there, and it can be, as you have said, mostly overdoing it, but it can be done differently, that's for sure. Nothing wrong with that, I'm a tweak freak too and forever will be. But just one more thing, and I'll try to express this in laymans terms, not because of you, but because of my limited knowledge on electronics so any corrections are welcome, please. The grounding issues in a guitar circuit are minimal. But amps runs at much higher voltages and frequencies especially and those are notorious to cause problems with multiple ground loops or improper grounding logics. In a guitar the signal is fed directly through passive components. The circuitry of amp is so diverse and full of components you have to make sure they are not interfering.

 

[Jason_The_Angry]

Re: conductive black paint in the control cavity? is this right?

... The grounding issues in a guitar circuit are minimal. But amps runs at much higher voltages and frequencies especially and those are notorious to cause problems with multiple ground loops or improper grounding logics. In a guitar the signal is fed directly through passive components. The circuitry of amp is so diverse and full of components you have to make sure they are not interfering.

Whew, I think we're going to need to start breaking this conversation into shielding and grounding! Related but seperate...

My suggestion, talk with some folks dealing with aircraft wiring and electronics for "the solution". There's some really wonderful, and outrageously expensive ways to deal with proper grounding and EMI. Like everything else, with enough time and money, an optimized solution could be found. I'd say the use of shielding paint and copper tape probably suffices for most of the issues that guitarists face.