Hummmmmmmm

[Marty]

I just finished the JP 42 tone mod found in this forum. All the switches work as they should, however I have a significant humming that only goes away when I turn either of the tone pots all the way down (meaning the opposite of the tone pots turned up so the sound is bright). I've attached the schematic from the JP Mod posting. Any solutions or ideas on where I should start tracking down the source of the hum. Hum?

http://music-electronics-forum.com/a...9&d=1169861231

[David Schwab]

One thing to look for with these types of mods is that the pickups' ground is separate from all the signal wires. For example, with 2 conductor pickup wires, the shield is also part of the signal, so if you were to flip the phase of that pickup, or run it in series, you will get hum because the shield is now hot.

Assuming your pickups both have four conductor cables, make sure the drain wires are grounded, and that they connect to the baseplate on the pickups, and that none of the signal wires go to ground at the pickup end. And check that your bridge is still grounded.

Other than that, just check all your wires, and make sure the back of the pots are all grounded. On the pots with the switches, there is usually a ground lug you can solder to, or on the side of the pot. If you don't have foil or conductive paint shielding in the control cavity, it would be a good time to add some, since you have a lot more wires in there now.

[Marty]

Now that you mention it, I don't recall having heard the humming until I plugged the guitar into an amp that is located in a room with a couple of low voltage light transformers right overhead. I wonder if RF from those transformers were source of the hum. Before that I was in my workroom playing through a personal amp with headphones. That room is lit using incandescent lighting. You may have saved me a ton of time looking for the problem. I'll test this when I get home and let you know. Thanks

P.S. I wouldn't mind my guitar humming if it would just hum along with what I'm playing.

[Marty]

One thing to look for with these types of mods is that the pickups' ground is separate from all the signal wires. For example, with 2 conductor pickup wires, the shield is also part of the signal, so if you were to flip the phase of that pickup, or run it in series, you will get hum because the shield is now hot.

Assuming your pickups both have four conductor cables, make sure the drain wires are grounded, and that they connect to the baseplate on the pickups, and that none of the signal wires go to ground at the pickup end. And check that your bridge is still grounded.

Other than that, just check all your wires, and make sure the back of the pots are all grounded. On the pots with the switches, there is usually a ground lug you can solder to, or on the side of the pot. If you don't have foil or conductive paint shielding in the control cavity, it would be a good time to add some, since you have a lot more wires in there now.

The hum seems to have gone away all by itself. My guess is that whatever RF the additional wiring was picking up is gone for the time being. Nevertheless, I have ordered some copper foil and conductive paint to treat the control cavity and prevent any futher occcurences. Thanks again for the advice.