P90 Grounding Question

Uncle Vinnie

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I have an 1996 R6, stock wiring.

Should there be a soldered-in ground between the two tone pots?

Getting a ground buzz. Haven't checked the input jack. Everything else looks good.
 

CB91710

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The pot shells should be grounded.
I'm assuming you have prior experience with single coil pickups? They can be noisy, pretty bad at high gain.
Does the buzz change when you:
1 - Touch the strings/bridge
2 - Switch to both pickups

I don't know if the Gibson P90s are RWRP, but that is a trick that Fender uses on the middle pickup to get a humbucking effect in the 2 and 4 "slot" positions.
 

Uncle Vinnie

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Does the buzz change when you:
1 - Touch the strings/bridge? YES
2 - Switch to both pickups? NO
I expect a little buzz with P90s, but this is excessive compared to my LP Pro Deluxe.
 

ARandall

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All 4 pots should be grounded.....either by a wire or a metal baseplate.
The typical wire horseshoe ground only connects on 3 sides (c shaped). So there will be one of the 4 sides that has no direct connection.
 

DarrellV

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The pot shells should be grounded.
I'm assuming you have prior experience with single coil pickups? They can be noisy, pretty bad at high gain.
Does the buzz change when you:
1 - Touch the strings/bridge
2 - Switch to both pickups

I don't know if the Gibson P90s are RWRP, but that is a trick that Fender uses on the middle pickup to get a humbucking effect in the 2 and 4 "slot" positions.
They were on my 2018 Classic Player.... AFAIK stock Gibby P-90's are hum cancel in the middle..
Someone on here was nice enough to point that out to me.:thumb:
 

efstop

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All 4 pots should be grounded.....either by a wire or a metal baseplate.
The typical wire horseshoe ground only connects on 3 sides (c shaped). So there will be one of the 4 sides that has no direct connection.
Connecting all four pots with wire creates a loop, a one turn coil, where EMI can come in. Base plate grounding does not. All four are properly connected with the C shape.

grounding pots
 

Tubejockey

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Your body catches all the noise in the room and your pickups do what they do. P90s are more susceptible to this as they are hotter single coils without shielded covers. Set the guitar down and step away, the noise should be less.
 

CB91710

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Connecting all four pots with wire creates a loop, a one turn coil, where EMI can come in. Base plate grounding does not. All four are properly connected with the C shape.

grounding pots
A shorted coil ;)
A one-turn coil would be if the ground wire were insulated, and looped around the cavity prior to being connected to the jack.

If Vinny has a Strat, a good comparison would be between the Lester and the Strat.
Same room, same time, same guitar, amp, and body position, same amp settings. The buzz will be there, and should be comparable.

Now remove the cell phone and tablet from the room, turn the computer and lights off.
LED lighting is a big improvement over CFL and tubes, but it can still be noisy, particularly with a dimmer.
 

efstop

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A shorted coil ;)
A one-turn coil would be if the ground wire were insulated, and looped around the cavity prior to being connected to the jack.
I'm just repeating what's in the article and it doesn't specify insulation :) but four pots connected on all sides would still be a loop, no? Most LP wiring I've seen is three sides only, or a ground plate. I'd like to try making a ground plate sometime and using that instead of the wire.
 

CB91710

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I'm just repeating what's in the article and it doesn't specify insulation :) but four pots connected on all sides would still be a loop, no? Most LP wiring I've seen is three sides only, or a ground plate. I'd like to try making a ground plate sometime and using that instead of the wire.
I only brought up insulation because it would prevent the loop from shorting.
But no... a shorted single-turn coil will not pick up enough EMI to produce noise. A single UNSHORTED turn of the ground wire in the cavity will not pick up enough EMI to produce noise.
You'll get more impact from the loop of wire under the pickup... and think back to those old coiled guitar cables.
 

Uncle Vinnie

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I'm not a tech, but everything looks good, and the input jack looks good.











 

efstop

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Um, this may be a dumb question, but why is there two sets of wire for each pickup? I can't find a reference or image for a P-90 wired like that. The wires to and from the switch look normal, but the control cavity wiring seems excessive.

Hopefully someone here knows what's up with that.
 

ARandall

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Thats a normal cavity.......braids from pickup to pots.....braids from pots to switch, single braid (with black ground shield) out to jack.
 

CB91710

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I am NOT liking the look of that solder joint, mister! :eek2:

View attachment 457606
Ya... Tough call, it looks like it's connected and there's just two stray strands.

But I agree... I'd probably resolder that one.

Js7DWKo.jpg


I don't see anything wrong in the cavity.
I do have a concern in that I don't see all three of the braided jackets soldered together at any single point, and I don't see a connection between the volume pots.
Normally, you'd have 3 cables in the switch pocket with all of the braids on that center ground tab, but I only really see one.
I'd like to see that switch withdrawn from the cavity before saying anything positively.


Back to the cavity... that's "modern" wiring.
Move the caps to the volume pot wipers for vintage wiring.
 

DarrellV

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Ya... Tough call, it looks like it's connected and there's just two stray strands.

But I agree... I'd probably resolder that one.

View attachment 457675

I don't see anything wrong in the cavity.
I do have a concern in that I don't see all three of the braided jackets soldered together at any single point, and I don't see a connection between the volume pots.
Normally, you'd have 3 cables in the switch pocket with all of the braids on that center ground tab, but I only really see one.
I'd like to see that switch withdrawn from the cavity before saying anything positively.


Back to the cavity... that's "modern" wiring.
Move the caps to the volume pot wipers for vintage wiring.
I'm thinking on this the braids all pick up ground from the switch and bring it to each set of pots..

That's why I'm even more concerned with a bad solder joint at the switch since it is the central point of all grounding in this case....
 

ARandall

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I guess as long as you have the braids touching at some point, then you have grounding between volume pots - even if its not direct.
 

CB91710

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I guess as long as you have the braids touching at some point, then you have grounding between volume pots - even if its not direct.
As long as they are soldered.
They are certainly "touching" in the channel to the switch.
Not seeing any braid in the switch cavity has me hoping that they are all 3 soldered to a pigtail that picks up the switch frame.

The guitar works and Vinnie didn't mention any intermittent noise, so I would assume that to be the case.
 


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