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noisy controls-Help!

I have had a problem with two of my piezo/pot combos. All that I am doing is controlling volume. The sound is clear when wide open to 10, but if I back off the volume I get a lot of hum.

I think that I am free of any ground loop... am using the better quality 500k pots from CBGitty and they are super-smooth. I am using terminal 3 as ground, and grounded to the pot. I have the hot from piezo to 1 and hot to the jack on 2.

any suggestions are appreciated.

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Permalink Reply by Skeesix on December 17, 2012 at 9:16am

Ground wire loose on piezo? I've had that happen.

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Permalink Reply by Ron "Oily" Sprague on December 17, 2012 at 10:56am

Despite the fact that you say you have no ground loop, iffen yer gettin' the hum at less than wide open, then, ummm, yeah, you do. You need to recheck your solder joints. At all points. Also, if you have a metal saddle ( like a bolt) then you need to ground that to the back ( not one of the lugs) of the vol pot, as well. Scrape off, really really well, the back coating of the vol pot to get to base metal, and attach all of your grounds to that point. Solder to that, and make 100% sure, using a multimeter, that your solder joints are good.

Check 'em twice. Then once more.

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Permalink Reply by Mark on December 18, 2012 at 11:18am

No, if he's using a piezo pickup there's no need at all to ground the bridge/saddle. You only need to ground bridge, strings etc. when using magnetic pickups.

Sounds like the right wires are connected to the right terminals. It's worth checking the existing solder joints to make sure they're not the source of the problem.

However it could be that wiring is actually OK. There are certain inherent problems with using simple piezos as pickups when plugging into a conventional guitar amp - mostly to do with mismatch in impedance - can be especially noticeable when you use simple passive controls. When you say you hear a lot of hum, can you give a better indication of how loud it is?

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Permalink Reply by ROBERT GREGORY on December 19, 2012 at 8:27pm

Thanks for the reply. The puzzling part is that I have a perfectly clear signal at wide open, and the hum only kicks in as I roll back away from 10. 1-9, hum. I wired one other CBG with the same type piezo and jack (no pots) and it is clear as a bell. The two CBG's that I am running thru volume pots are making the exact same noise. Could it be the pots inducing some noise?

I have everything on the ground side bonded to the pot and the ground terminal on my pot (#1) is bonded to the pot back as well. The output from my pot is on #2 and runs straight to my jack. The positive from my piezo runs to number 3 terminal. Does that sound right?

The hum isn't super loud and, I can dial it out if I roll off all of the mids and highs on my amp, but who wants to do that? BTW it stops if I touch my jack plate. My meter shows continuity between my plate and the negative side of the output jack. So, I didn't run a ground to the jack plate, should I?