I have a Fender Telecaster that hums loudly--much more so than other similar guitars. It's a standard Tele with single-coil pickups. The humming noise stops when the player touches the strings or other metal parts of the guitar. The guitar is plugged into a simple solid-state guitar amplifier. The humming noise sounds like 120Hz hum (see update below). I've tried plugging into a different outlet, turning off all the other electrical devices in the room including the lights, etc. Nothing helps.
I would like to understand:
- What is causing the hum? I know it's "mains current" or something like that. I would like to understand what is actually happening.
- Why does this guitar hum much louder than a Fender Stratocaster, which also has single-coil pickups?
- Why does touching the strings cause the humming to stop?
The strings and other metal parts of the guitar are all connected to the jack and cable sleeve and all comprise the "ground" of the guitar-amplifier circuit. The cable sleeve is in turn connected to the metal amplifier chassis and ultimately to the mains ground.
I'm posting this question here because whenever I search for information about this on the web, I find all sorts of answers/explanations from people who don't know much about electronics that all contradict each other.
Some explanations I've heard:
"Ground loop." Ok, where's the loop? It's just a guitar plugged into an amplifier. This "explanation" is usually followed by advice to "break the loop," try removing/re-installing wires, use a ground-lifting cable or device, or something like that. How can I diagnose a ground loop like an engineer, maybe with a multimeter?
"Loose wire." The person providing this answer recommends checking solder connections etc. In the same thread, people have pointed to the fact that touching the strings eliminates the hum as both evidence of there being a wire loose ("your body completes the circuit!") and of there definitely not being a wire loose ("your body is being grounded through the guitar").
"Not enough shielding." Maybe? But why does touching the strings cause the humming to stop (after all the electronics are still unshielded right?) and couldn't we just do whatever touching the strings does, electrically, and thereby stop the humming?
"Your body is an antenna/capacitor plate." This explanation suggests the there is some potential being generated in the player's body that is being transferred to the pickup and that touching the strings grounds the player. This explanation seems promising but is always presented in a hand-wavy manner. Okay, so my body is an antenna, but why does that cause the guitar to hum, and why don't I cause other electronic devices to hum as I move around the room?
"Everyone knows Telecasters hum, just get used to it." I'm having trouble accepting that Fender would continue to produce a guitar that hums like mad when they obviously have the technology to mitigate the problem, as evidenced by the behavior of the Stratocaster in the exact same situation, in the same place, plugged into the same amp. I understand that single-coil pickups hum, but the Stratocaster hums like, well, every other Strat, while the Telecaster hum is obnoxiously loud.
The question was answered on Music: Practice & Theory Stack Exchange, but the answer there is typical of what I've found online. The answer is "grounding and shielding" and advises checking wires, changing components, etc. Someone brings up the "your body is an antenna" explanation in the comments. There's no explanation of what is actually going on.
I'm hoping that by posting this question in EESE, I can get a more satisfactory/scientific answer than the ones I've found so far.
Update to this question, 21-Sep-2019: I was able to do more investigation of this issue. I checked the grounding and confirmed that there is continuity all the way from the strings to the cable sleeve to the amp chassis and to the ground in the wall power socket. So whatever the problem is, it's not a missing or floating ground. Also, I took the guitar to a different location, with a different amplifier, and in that location, with that amp, the hum was greatly reduced and was more like typical single-coil pickup hum. I checked ground continuity in the new location, and it was fine. So it's some issue that is at least partially environmental (having to do with either the amplifier or the place) but only affects this guitar, or at least affects it more than it does other single-coil guitars like the Strat.
Another update: Actually the noise isn't a 60Hz hum; it sounds like the 120Hz "angry insect" hum that is often associated with ground loops. But I can't identify a ground loop here. The guitar is just plugged into one amplifier, which is plugged into one wall outlet.