P90 phase switch

[Michael R]

Here's the situation:
My guitar has a two P90 setup and I upgraded it with DPDT phase switch for the neck pickup (SP90). The problem is HUM.
I thought that phase switch doesn't affect pickup's tone when exact pickup works but mine does! Not even tone slightly changes but hum appears when I switch to normal position.

What's wrong or is smth wrong with it?

Topic's closed! Thanks everybody!

 

[Funkfingers]

Re: P90 phase switch

Er, P-90s are single coil pickups. Used singly, they are always prone to RF interference.

Only when used as a pair is it possible to cancel hum. One P-90 has to be reverse wound and reverse magnetic polarity (RW/RP) with respect to the second.

Reversing the polarity via a DPDT switch negates the RP component. Hence, no more hum cancellation.

 

[Michael R]

Re: P90 phase switch

Yes, right, BUT
When I use neck pickup only there is a lot more hum (especially when I don't touch strings) in "normal" position.
Well...there're three hum levels now:
1. No hum (Both out of phase)
2. Regular noise (Single pickup work or both phase (bridge, neck in "out of phase" switch position))
3. More noise (neck pickup only, "normal" phase switch position)

 

[Zhangliqun]

Re: P90 phase switch

If they are braided leads, you have likely put one of the P90's baseplates on the hot side of the circuit in one of the positions on your phase switch, which means that whatever noise the baseplate picks up from RF, 60-cycle, etc., is being sent directly to your speaker instead of to ground.

Whether P90's or humbuckers, braided lead pickups are bad candidates for phase reversal for this reason. The ground lead from the coil is soldered to the baseplate, as is the braiding.

You need to convert one of the P90's (the one whose phase is being flipped) to a 3-conductor (hot, ground, bare wire/shield for baseplate ground) to avoid this extra noise. The baseplate needs to have a separate lead to ground so that it remains grounded at ALL TIMES.

 

[mudpuppy]

Re: P90 phase switch

If they are braided leads, .....

Check the picture, Zhangliqun. You nailed it.

 

[Zhangliqun]

Re: P90 phase switch

I was going by the picture too, but just in case my eyes had gone even further south than I thought and those braids were off the pickup selector switch or something, I hedged my bets.

 

[Funkfingers]

Re: P90 phase switch

I would like to know about the green and blue cables from the neck P90 to the phase inverter switch.

If these are the two ends of the neck P90 coil, there ought to be a third conductor for grounding the pickup's metal baseplate.

Judging by the photograph, the blue cable might be emerging from a braided screen but the light green cable is not.

If you appear to have "switchable hum" it is because your DPDT switch is altering the grounding status of the neck P90's baseplate. In one mode, the pickup works as it should. In another, you have turned the baseplate into an RF aerial - exaggerating the hum.

 

[Michael R]

Re: P90 phase switch

light blue cable soldered to the screen and the blue one is hot. Where should that third conductor be soldered? If I permanently ground baseplate would that switch work at all?

 

[Michael R]

Re: P90 phase switch

Ah! There is one thing I can do with it but...I need to replace wire from pickup...I don't want to. Well, is it serious that baseplate becomes an RF aerial?

 

[Michael R]

Re: P90 phase switch

Yss. now I understand where problem is. The question now is: is it really the problem?

 

[super rad stuff]

Re: P90 phase switch

if you're getting more "hum" than usual with the neck pickup and it's more pronounced when you let go of the strings, i'm assuming that it's because the guitar has a grounding issue.

 

[uOpt]

Re: P90 phase switch

These are {1-conductor plus shield} wires.

You cannot put them out of phase except by fliiping the magnets.

If you just switch phase at the wires you would put one shield'n'ground on hot and that's gonna hum like a mofo unless you sit yourself in a Faraday Cage.

 

[Michael R]

Re: P90 phase switch

Thank you guys! Now I know what's wrong. There's actually three mistakes in wiring and grounding and I'll solve them all soon.
Thanks!

 

[Funkfingers]

Re: P90 phase switch

The solution to your problem involves partially disassembling the neck position P90 in order to desolder the original output cable and attach a new one.

If you are anything less than totally confident about this modification, hand the job over to an experienced guitar repairer.

The new cable should be two conductor + shield. The two colour-coded output conductor cables should be soldered to the start and finish ends of the pickup coil, respectively. The shield wire should be soldered to the pickup's baseplate.

At the controls end of the cable, the two output conductors go to your phase inverter switch. The shield wire should be permanently soldered to ground, typically on the chassis of the volume of tone pot.

There will be no need to do anything to the magnets of the pickup.