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Wiring problem

Haven't built anything in a while, but I got a hair to build a "nice" guitar, a four-string electric. Looking for a mellow "hollowbody electric sound.

Got a nice big Las Cabrillas box...

Got everything done over the weekend and started to wire the thing up. I'd decided to use the P-Bass pickups from Gitty and followed this wiring diagram, pretty simple:

http://www.seymourduncan.com/support/wiring-diagrams/schematics.php...

Got it done, did the "tap test" on the pickups and all seemed fine. Both volume and tone worked, good signal.

I put the strings on and.... Not so good.

I'm getting a strong buzz whenever I touch the strings or the grounded tailpiece. Buzz decreases greatly when I take my hand off.

Buzz almost goes away when I hold the output jack.

Very low signal...It's there, but not loud at all. I ran it through both my amps, my little Honeytone and my Behringer practice amp.

My gut feeling is that it's a ground problem, but I followed the diagram and can't find any visible fault.

Also, the strings are quite far away from the pickups; I might have to re-do the way the PUs are mounted.

Any clues as to what to look for?

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Permalink Reply by robert jones on October 5, 2013 at 11:07am

Reversing the leads at the jack would change the phase of the signal to the amp, wouldn't cause the noise you describe.

Anyway, be easier to determine the solution to the difficulty if you could provide a clear photo of the problem circuitry.

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Permalink Reply by The Phrygian Kid on October 5, 2013 at 3:06pm

Actually I'm betting it will improve things immensely.
Because I still think you've wired the bridge/strings to hot, so flipping the phase of the output will correct this....

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Permalink Reply by robert jones on October 5, 2013 at 11:21pm

I would think adding the ground connection that is missing in the linked schematic would have more affect on the problem described...simple enough to sort out if he'll post a pic of the actual wiring.

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Permalink Reply by David McQueen on October 6, 2013 at 3:43am

I got fooled by this. Go to the link and then click on the picture for a magnified view. The the missing ground link shows.

But agreed - post a pick of the actual build.

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Permalink Reply by Mark Werner on October 6, 2013 at 6:45am

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Permalink Reply by The Phrygian Kid on October 6, 2013 at 7:16am

There appears to be no continuity between the chassis of pot a and the chassis of pot b. Therefore the only signal which actually makes it to ground is what you bleed through from the hot side when the tone control is open, ie your tone control will be working as a kinda reverse volume control. All you really need to do to get it working is bridge the gap between pot chassis. This demonstrates a kinda shortcoming in a lot of guitar circuit diagrams imho, there is no common earth but the pots are all connected in a loop or star and then the whole thing is treated as a common earth. Easier to wire everything to the sleeve of the jack connector. You may know that you are operating both these coils in series all the time?
They'll certainly work like that, and be noise cancelling and nice and powerful to boot, but most guys clip the connecting wire between and treat em as two pickups

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Permalink Reply by John Sawyer on October 6, 2013 at 7:22am

First: I know my electronics, but not my pickups, so this is a question more than a statement: It looks to me that the polarity is reversed between the two pickups. . . so if we think of the pickups like a battery, the left pickup has a red wire on the right I will assume is + and the black is ground. If I assume the pickup on the right is the same polarity, this would be like wiring 2 9v batteries ground (-) together and expecting to see a voltage between the two + poles... if these are wound the same direction, wouldn't they cancel each other out? -Apologies for the hijack. Back to your regularly scheduled program.

John -Guitar noob

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Permalink Reply by robert jones on October 6, 2013 at 9:01am

Photo of wiring shows that most likely Mark didn't zoom in either since lack of the amazing suddenly appearing ground connection is the problem with his wiring...crazy way to display a wiring schematic.

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Permalink Reply by Mark Werner on October 6, 2013 at 9:10am

Someone else (on another forum...I floated this to several) pointed out the lack of connection between the two pots.

Of course, most guitars have conductive shielding... I didn't think of that.

So, just a Jumper wire, or should I pull them out and glue in a section of tinfoil or some-such?

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Permalink Reply by David McQueen on October 6, 2013 at 10:18am

1. Run a ground from the back of your volume pot to the ground lug on the jack and give it a try. That should give instant improvement.

2. If you are still getting odd things, try foiling the wires to give them a shield of sorts. On the next build, if you are not using shielded cable, twist the hot and ground wires together and the ground will give some shielding to the hot wire.