Originally Posted by Trow
So I grounded the - of the input jack, and I grounded the two pots and the only thing that changed was now the hum increases whenever I touch anything metal: strings, bridge, even the tuning pegs. So... any idea whats wrong?
Let me explain "grounding". If you already know this, I apologize for sounding condescending.
"Ground" in electronics is the return path for electricity to flow. Electricity won't flow if it cannot complete a circuit. A switch, for instance, opens the circuit and electricity won't flow through that circuit until the switch is closed again. "Ground" gets its name from the earth, to which all electricity eventually flows.
You should be able to plug your guitar into your amp and read < 10 ohms of resistance from any metal part of the guitar to the ground prong on the amp's power plug. If you can get this reading, your guitar should be properly grounded. If you do get this reading and you still have the noise problem, try plugging your amp into a different socket in the house to see if the problem goes away. If it does, then you have a problem with the ground wiring on the first plug. If the noise doesn't go away, take the whole setup to another house or building and plug it in there and try it. If the noise goes away your house has a ground problem.
Be very careful if you find your house has a grounding problem. Improper grounding of electronic things that require a good ground can kill you if you touch the wrong thing at the wrong time. An example: touching your guitar strings while plugged into an amp and touching a microphone that's plugged into a PA system with your lips. Your body is the link between those two ungrounded circuits and if the voltage potential is high enough, you get zapped. Or killed.
If your house has a grounding problem, you need to get a qualified electrician to fix it ASAP. Don't plug your guitar amp into an ungrounded system. If you were to touch anything electric while touching the guitar, you might be electrocuted.
You can get an inexpensive tester to check home wiring at any Home Depot or Lowe's. Cheap insurance.
Now, on to your guitar's ground circuit: The "-" side of the jack is where all grounds inside your guitar run to, electrically speaking. All those black wires that congregate on the back of the pots are the grounds from all pups, the bridge, and anything else that needs a ground. Then one wire runs from the pots to the negative side of the jack. That side of the jack makes electrical contact with the barrel of the input cable; the other end's barrel makes electrical contact with the amplifier's ground circuit and out it goes to the power plug and eventually to earth through the house wiring. If you have all of these conditions, you have a properly grounded guitar. At this point touching the strings should have no effect on any humming or static noise.
Some hum comes from the pups. If you have humbuckers that hum should be minimized. Single coils like most found on Fenders are more susceptible to hum and there's not a lot you can do about that. This hum will not change by touching or letting go of the strings.