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P/J bass buzzing woes.


Grassie
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I have a P bass that I converted to P/J a couple of years ago, and I recently bought a new wiring kit (solderless V/V/T) off of our very own Ki0gon. I've had to route out the cavity some more to accommodate the larger pots so I repainted the cavity using shielding paint. I connected the pickups as per the usual wiring diagrams and grounded to the bridge as usual. 

The issue I now have is that with the bridge pup turned up I have a horrible buzzing noise made even worse when I touch the bridge or strings or knobs. I don't know what I've done wrong. The split coil soloed is quiet with a very slight click when I touch it but it's unusable when I turn the bridge pup up.

I'm ready to start smashing stuff up...

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That J pickup.  Is it a single or a stacked coil one? 

Forgive me if I'm stating the obvious:

The way the P pickups work is that they are actually humbuckers with the magnets in different directions and the coils in different directions.  The signal from the strings adds but the pickup from nearby electric fields cancels out.

A standard J pickup is not humbucking as it only has one coil.  With a full Jazz Bass the two pickups are wound and magnetised in oppposite directions so they individually pickup noise from the surroundings but when added together do not.

So, if you add a non cancelling J to a cancelling P the noise no longer cancels and you get some hum.  The solution is to use a stacked coil J pickup which incorporates its own cancelling.

My J bass now has two stacked J pickups and is totally silent whatever balance I use, but previous incarnations were quite buzzy and did stuff lke pick up police radio and local taxis (pre mobile phones!!)

If its REALLY noisy you might have some other electrical fault - eg it's accidently wired up back to front so that the earth (strings etc) are accidently connected to the amps input and vice versa.

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Nick A's point is sound. Homemade PJs - where people simply add a standard J bass bridge pickup to a P bass - often suffer from hum/buzz because of it. Fender PJs use a hum cancelling J pickup to counteract this. Shielding paint is not the best thing to screen body cavities in my experience.  You can get self adhesive copper tape (via Amazon, eBay and others) which is much more effective.

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22 hours ago, NickA said:

That J pickup.  Is it a single or a stacked coil one? 

Forgive me if I'm stating the obvious:

The way the P pickups work is that they are actually humbuckers with the magnets in different directions and the coils in different directions.  The signal from the strings adds but the pickup from nearby electric fields cancels out.

A standard J pickup is not humbucking as it only has one coil.  With a full Jazz Bass the two pickups are wound and magnetised in oppposite directions so they individually pickup noise from the surroundings but when added together do not.

So, if you add a non cancelling J to a cancelling P the noise no longer cancels and you get some hum.  The solution is to use a stacked coil J pickup which incorporates its own cancelling.

My J bass now has two stacked J pickups and is totally silent whatever balance I use, but previous incarnations were quite buzzy and did stuff lke pick up police radio and local taxis (pre mobile phones!!)

If its REALLY noisy you might have some other electrical fault - eg it's accidently wired up back to front so that the earth (strings etc) are accidently connected to the amps input and vice versa.

It's a standard jazz pickup as far as I'm aware. I used to have this wired as a stack-knob - ie two stacked pots for each pick up, and this didn't give me any problems. Here's a photo...

 

PJ wiring.jpg

Edited by Grassie
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I can't quite see what is wired to what, but it looks like your J pickup may be connected back to front.  Ie the black and white wires are going to the wrong holes in the little terminal block.  That would cause noise to add and signals to cancel.

Try swapping the wires around (no guarantees).

If you really want to do it properly, then a) get a stacked coil J pickup,  b) twist the pcikup wires together  and keep them as short as possible (better still, use co-ax cable from the pickups to the control cavity) c) use screening foil or conducting paint inside the pickup cavities and the control cavity and make sure the surface of the cavities is connected to the bridge / pickup / jack-socket grounds.

A lot of people swear by copper foil for screening, but if you look inside a quality factory made bass (certainly, both my Wal and Warwick) you will find they are use conductive paint.  My project J-bass has painted cavities and has been totally silent, even with standard J-Bass wiring (as you have) since I got the stacked pickups.  The problem is, you NEED the pickups to pickup magnetic fields otherwise they can't see the strings, but really don't want them to pickup anything BUT the strings .. screening the cavities can only do so much as there is always a dirty great hole in the front of the pickup cavity!! 

If all else fails, I'm only down the road in Derby and happy to take a look for you.  You'll probably find another guitar playing electronics engineer closer, but the offer stands.

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She LIVES!!! :D

Thank you guys for the advice, tips etc. I did indeed have the J pot wired up wrong. I've also grounded the tone pot to the shielding. Result? Practically zero hum, no buzzing and a great set of tones thanks to the KiOgon wiring loom. 

I've strung her with a fresh set of Dunlop Super Brights (40-100) and will give her a good seeing to on Friday night....;)

Thanks again everyone. Basschat RULES! :D

 

20180514_190808.jpg

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11 minutes ago, rushbo said:

I have no technical advice to add to this thread, but I need to compliment you on an incredibly handsome bass. 

Thanks mate! 😊 She got her first gig last night, sounded great with the Dunlops on there, I'd forgotten how comfortable it is to play - I've been using my Sire V7 for gigs and although that too is a great sounding bass, they are a little on the heavy side. The P/J is a bit lighter but doesn't' feel insubstantial like some lighter basses. It certainly sounds heavy with the new pots. 😁

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