Split P Bass pickups and hum.

[Stratz]

I just installed a split P bass pickup in a custom Jazz bass. I routed the neck slot for the split P bass pickup, built the P bass pickup (RW/RP), installed it and there's what sounds like 60 hz hum. The bridge ground is wired up to the back of the pots but the hum is the same sound as if it weren't.

The bridge pickup is a Fender Noiseless Jazz bass and it's dead quiet.
The control/wiring scheme is Bridge Vol, Neck Vol and master Tone. 250k CTS pots with a .022uf disc cap.


I also noticed a little out of phase sound when the P bass pickup is turned up from about 9.5 to 10.
The hum is present whenever the P bass pickup is brought in to the mix.

Thanks for any recommendations.

[mr fab]

I guess I am stating the obvious, but did you wire the pickup halves start to finish?. did you check each half for resistance? you may have a broken winding

also check that the pot is earthed using your ohmmeter

[Stratz]

I guess I am stating the obvious, but did you wire the pickup halves start to finish?. did you check each half for resistance? you may have a broken winding

also check that the pot is earthed using your ohmmeter

Yes sir. I checked all of the above. It's wired in series and reads ~11.5k and the pots are all grounded but the hum is still present.
Thanks for the suggestions though.
This can be very aggravating.

[big_teee]

I've had noise issues with P-bass pickups in the past.
Fender must have had these issues too.
That is probably why he put the brass ground plate under the pickups.
Aluminum foil on the full pickguard helps too.
The vintage 71 set I rewound, the bass coil was wound CW finish to the ground plate.
The Treble Coil was wound CCW + output to the start lead.
The finish of the Treble coil was tied to the start of the bass coil.
On my own sets I wire them outside in.
+ output to finish of treble coil, ground on start lead of bass coil.
Coils are wound RWRP.
GL,
T

[David King]

Something is wrong, have you tried grounding the magnets? The 4 strings have equal volume?

[Stratz]

David, all strings sound fine and equal volume. I'll try removing the lacquer and putting a strip of copper shielding across the bottom of the magnets then to ground. If this works I'll order a P bass plate. Still still dont understand why they would hum though.

Do you think grounding also has something to do with the slight out of phase sound when I turn the P volume from 9 to 10 when the Jazz bridge pickup is on?

Thanks

[mr fab]

that slight out of phase sound has me curious and I am sure the key to solving this issue. do you insulate the magnets or lacquer them? if lacquered, you may have a short to one of the magnets...

[Stratz]

I dip them in lacquer twice to seal the bobbins and hold them together. Before I wind them I always insulate the rod magnets with polyimide. No shorts to the rod magnets.... ever.
I've heard the same slight OOP sound on Jazz bass pickups that I've installed as well. Never figured this out.

I'll be trying the grounding as soon as the customer brings the guitar back for me to install a new bridge pickup.

Anymore suggestions guys?
Thanks for the replies.

[rjb]

I'll be trying the grounding as soon as the customer brings the guitar back for me to install a new bridge pickup.

Anymore suggestions guys?

If the grounding doesn't fix it, I'd do the "isolate the problem" routine. How does the pickup sound wired directly to an output jack? Through the volume pot? Through a different volume pot?

[Stratz]

Thats on my list when I get the bass back.
Thanks!

[David King]

The diminution of volume between 9-10 when two pickups are mixed is due to the slight difference in signal phase resulting from the pickup's differing locations. The further they are apart the greater the cancellation. One way to deal with this might be to connect the two pickups in series rather than in parallel.

Grounding the magnets is different from adding the brass plate to the back of the cavity. The ungrounded magnets (if they are conductive) act as noise antennas, same as the strings and the player's body which is why we ground the bridge. You'd be better off shielding the whole cavity with conductive paint or copper foil though you may want to slit the corners of the shield to minimize eddy currents.

The best way to maintain a magnet ground is to use the nickel conductive paint on the back of the flat work and apply copper tape (with conductive adhesive) to that to allow a solder joint. You can apply the copper tape directly to the magnets but you need to keep direct pressure on the back of it to maintain a connection. The springy foam blocks work pretty well for this.

[Stratz]

Thank you David. Great information.

[Sock Puppet]

Have you checked that the magnets in one half are opposite polarity to the other?

Otherwise it won't be humbucking...

[Stratz]

Yes sir

[big_teee]

Have you checked that the magnets in one half are opposite polarity to the other?

Otherwise it won't be humbucking...

That's not the case.
"Reverse Wound is What Cancels Hum, and Polarity is what sets the Phase."
We have that chiseled in stone on the B/H forum.
With the two coils end to end, the magnet polarity doesn't matter for the operation of the Split- P.
The phase of the P magnets does matter to the J pickup when played together.
The 3 coils will never cancel hum when all three played together.
any of these will work.
P--N/N
J--N

P--N/S
J--N

P--S/S
J--S

P--S/N
J--S