As in, where do you solder all the wires that go “to ground”?
I’ve my project guitar almost all done. I’ve soldered all of the “to ground” connections to the back of the volume pot, but when I plugged it in to test there’s an ungodly amount of hum. If I touch the volume pot, the hum goes away, which means (I think!) the volume pot itself isn’t grounded. Knowing next to nothing about electricity, I don’t know what to do about it.
Help? Thanks!
I have a couple of project guitars, and I shielded the cavities with copper tape. One 2" roll was enough to do two Telecasters. The tape is grounded, and the cavities are connected electrically by soldering a wires to the tape.
And here’s an article on how to shield a Strat.
One side of the wire from the pickup to the amp should be grounded, and the amp itself should be grounded with a proper 3-wire plug. Connecting everything to the back of the pot is good, but that doesn’t help if the pot is floating.
Another article, with pictures.
A google search indicates there are videos, but I haven’t looked at them.
and not only is the above a performance issue but also a safety issue. people have died when their instruments weren’t properly grounded.
Ive got a wire from the back of the pot to the ground part of the jack, and the amp is grounded (fender princeton, 3-prong plug). Shouldn’t that ground the pot?
Are your pot knobs metal Earthworm Jim? If the guitar wiring ground goes to the pot, and your amp is grounded, then I’d suspect that the strings are floating. The earthing point for this is at the bridge.
Ditto johnpost’s point, the guitar amp should always be earthed. But usually this is the only point in the setup that has a connection to the planet; two or more earthings will produce earth loops that will pick up extra hum and interference.
That certainly should do it.
The pots are metal.
I took the whole thing apart and shielded the cavity. There were a couple of extra-long wire runs, so I shortened those up. I tested with the multimeter between the jack body & bridge, jack body & volume pot; pretty much everywhere.
I also tested between the “hot” side of the jack and the ground, there was no current.
But I’ve still got terrible buzz on the individual single coils which disappears when I touch the outside of the jack. The buzz also disappears when I turn either volume or tone all the way down, and gets much worse when I touch the pickup itself.
All the clues here point to a floating earth somewhere - I suspect the strings are floating, but you say the bridge is connected to the common ground. Hmmm…
Here’s something to try: Plug a jack lead into your guitar, but nothing else, leaving the amp end of the lead unconnected. With the guitar volume pot at maximum, and the tone control set to the brighter end (or half way if in doubt), connect one end of your ohm meter to the body of the free jack plug, and buzz out the ground connections in your guitar. In particular, buzz out the connection to the strings.
A guitars pickup coils are very good at picking up mains hum. If the strings are floating they’ll pick up mains hum and radiate this to the coils. The body of the guitarist will also pick up mains hum, and radiate this to the coils also. I think your ground connection at the guitar jack output and pot is OK, as it’s grounding the mains hum from your body when you touch the volume knob or the output jack body.
If you can’t find the culprit connection, post the schematic you worked from and photos of your wiring. Don’t worry, the problem is fixable. I’m assuming you can get a decent signal underneath all the hum; if not, that would point to an open coil.
I can’t find my camera at the moment, so no picture, but here’s a link to the schematic I worked from; and I followed Johnny’s “How to shield a strat” link as best I could given this is a tiny little rear-routed control cavity. I plugged in the cable as Fridge suggested and tested connections again, from the cavity shielding, the bridge, the back of each pot, and the point where all the pickup grounds come together - good signal all through.
Just for grins I plugged it up to a different amp (Mesa triple rectifier) and it sounded great, and it was quiet when I wasn’t playing or touching it. Not silent, but quiet. But when I plugged it back into the princeton I had the same problem again. Tons of noise and even some whistling, almost like microphonic feedback.
I begin to suspect part of my problem is a bad volume pot, because the signal dropped out completely while I was playing. A couple of taps on the volume pot & it came back. Le sigh, that means I’m going to have to unsolder the pot & put in a new one - what a pain! And I’m going to have to try another guitar with single coils in that princeton.