Thunderbird Issue

[David Payne]

I put together a Thunderbird from a body blank and vintage neck for a customer. He gave me all the parts so I don't know their exact history.

After he had the guitar for a while he began noticing a burst of noise intermittently while playing. I have checked the jack, pots and grounding and everything seems fine. However, I noticed that when I play over one set of poles on both of the humbuckers (Mighty Mites), I get a buzz that is like 60 cycle plus some static.

My guess is he gets this noise when he plays near or over the particular row of poles. Both pickups have this issue and there is a constant low level hum/static sound in the background. When I grab the ground of the cable jack or really plant my fingers on the strings the background noise drops to almost nothing.

If I touch the particular row of poles it really lets out a burst of noise. Both pole rows look identical so I can't tell which side of the humbucker is really being affected (hot or ground). On a guitar I can tell because there is a row of slugs and a row of adjustable poles.

Anyway, I wondered if any of you could suggest some theories. Humbuckers obviously are not supposed to hum.....

Thanks,

[Russell Vance]

All the usual suspects -
1. check the grounding wire from the bridge/stoptail to the guitar earth (usually the back of a pot)
2. remove each of the pickups from the circuit and hardwire them to the amp individually.
3. measure and test each individual winding (and the series link) separate from the guitar circuit
4. configure the individual windings to check for hum cancellation - wiring colors aren't always right.
5. test each pickup in the guitar electrically isolated from each other - then combine.
6. use a 'known good' pickup to substitute and check for difference (the most important step)
7. Physically destroy bad pickups so the next poor unsuspecting tech does not have to go through the same thing.
8. left field: if the bridge has plastic or Graph Tech saddles make sure the ground wire comes from the stoptail as the plastic will isolate the earth if the bridge is the earth connection.
9. Asymmetric wound humbuckers like Gibson Burstbuckers and Bare Knuckles will has a slightly diminished hum rejection (they are a bit noisier in the quiescent state) but, that the price we pay for tone. And, if you turn up anything loud enough it will hum - especially with high gain amps and analogue effects.
I'm sure I;ve forgotten a few but, Hope that helps. Rusty.

[FRANK]

RUSTY YOUR A GOOD MAN

[David Payne]

Thanks Rusty.

I had thought of disconnecting the pickups and soldering a jack straight onto each one but I had not considered the other possibilities. These a symmetrical humbuckers and you don't have to turn them up very far to hear the problem. I need to research the pickups but I think they might be kinda chessy. They are potted so I can't really check the internal wiring like you can on some pickups by carefully removing the tape on the bobbins etc.

Dave

[Len Biglin]

David as you have a noise that goes when you ground your body , I would be grounding the strings via tailpiece or bridge , that grounds you and the noise . That should be all thats needed , and follow Rusty's tips on graphtech saddles etc.Len

[Ted Kritikos]

I'm just guessing here, but you might have the pickup wired incorrectly. Just from checking online, the mightymites seem to have 3 leads coming off them, a red spliced wire for coil tapping, a white hot wire, and then some other wire which I bet has the cover of the humbucker attached to it as well as the ground of the pickup. If that wire is hooked up to your pot, touching the cover or pole pieces will make noise like touching the end of a guitar cable. Also, if just the red wire is hooked up, you might only have one coil going, so you wouldn't be canceling any noise.

[David Payne]

These pickups are potted with an epoxy type material and only have a white jacketed mini coax coming from each, I assume the shield is ground and center is hot (or signal).

Thanks,

Dave

[David Payne]

Hi everyone,

I looked under the bridge and was suspicious that the metal had some kind of passivation (anti-corrosion coating) on it so I sanded it to a bright finish and reinstalled the braided ground strap that goes directly to ground in the control cavity. The noise problem flat out disappeared.

Thanks to everyone for the suggestions.

However, I am also doing setup on this one and it has a vintage neck that is not straight but probably usable. I have done as much as I can with the truss rod adjustment and leveling and re-crowning the frets. After all that here are the specifications:

1. With a capo on fret 1 and fretting the strings at the 14th, I have .020" neck relief at the 8th fret.

2. The string height at the 14th is a little less than 3mm (.120") from the top of the fret to the bottom of the bass string. It is 2mm (.080") in the same place under the treble string.

I have lowered the bridge saddles as much as possible until just before it buzzes. The same with the nut....the slots are as deep as I can take them without getting open string buzzes.

So, does anyone have input on whether they think this setup is about right? The only thing I can think of is to shim the bolt on neck a little to get a negative neck angle and slightly reduce the string height up around the 12the fret and beyond.

I am a guitar person and not as experienced when it comes to basses.

Thanks in advance,

Dave