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Volume pot hum...

I just ran into a problem I've never had before. When I plugged my guitar into a regular sized amp (as opposed to my 9 volt Honeytone amp) everything sounded fine when the volume was turned all the way up but when I turned the volume down, a very annoying hum popped up.

As in all my previous builds, I had parallel piezos wired in with a volume pot. I used an inexpensive 1 M pot from Gitty and I thought that might be the problem. I used two wires twisted together as I had in other guitars for all the wiring. I replaced the wiring with a shielded coax wire and that buzz totally disappeared.

Anyone have any guess why I would have this problem now when I never had it before. (I did plug in all the previous builds that I still have and none of them had that problem.)

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Permalink Reply by Jim Saraceno on December 20, 2016 at 6:35pm

Well, the problem was fixed when I replaced the twisted pair of wires with the shielded conductor so I know it is not the pot or grounding issues.

The reason I went with the 1M pot is in the Gitty description they said... "Higher-resistance pots such as these are often recommended for use with disc piezos, as they are better matched to the piezos' high impedance.

I previously used 500K pots and I can't honestly tell the difference in performance.

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Permalink Reply by Jim Saraceno on December 21, 2016 at 3:23am

No worries Wayfinder. As I said, I have used twisted pairs for many of my builds with no problems. As far as the proper matching of pots and piezos, I'm totally clueless. I've never experimented to see how different resistances affect the sound, I'm just going on what I have read here and on Gitty's website.

It is just so odd that I would have this problem on one guitar but not on three others that were wired similarly.

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Permalink Reply by Wichita Sam on December 22, 2016 at 1:40pm

florescent lights in shop/work area? I switch to halogens and a lot of the buzz issues went away.

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Permalink Reply by dave price on December 22, 2016 at 1:35am

A couple of things come to mind. First when using the battery powered amp the voltage is clean , The regular amp takes its supply from the mains. The D.C. Voltage carries a small ripple which can be picked up by Piezo sensor and 1meg pot.. Therefore good grounding is necessary. Is the pots metal cased. If yes connect the ground / common to the case.

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Permalink Reply by Jim Saraceno on December 22, 2016 at 3:13am

Thanks. I always ground the case. Actually, when I first wired this guitar, I had a huge buzz then realized I had mixed up my wires and grounded the outer ring of the jack instead of the inner ring. I swapped the wires and that took care of that problem. It wasn't until I plugged into a full amp that the volume turned down buzz popped up.

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Permalink Reply by Paul Craig on December 23, 2016 at 9:33am

A bigger AC powered amp is going to be more sensitive to RF noise from a hollow bodied git. This is why the shielded wires fixed the problem. I've started using this kind of wiring for my CBG's. If you don't have access to this kind of wiring, twist the negative and positive wires together from the jack up to the volume pot.(not meaning to connect the 2 wires, but wrapping them around each other while still being insulated from one another)
Lining the inside of the box with aluminum tape, copper tape or shielded paint is also a great idea for keeping the noise down with piezo's and single coil magnetic pickups.