A hum that is present with no cable connected comes from the amplifier or the mains, not from the guitar. Try a different socket and a different room before assuming the amplifier is at fault.
Isolate it in two minutes
No cable, hum present: amplifier or mains. Cable plugged in but not the guitar, hum appears: the cable. Guitar plugged in, hum appears: the pickups or the room.
What often fixes mains hum
A different socket, ideally on a different circuit, and removing chargers and dimmers from the same extension lead.
What does not
A more expensive instrument cable. If the hum is there with nothing plugged in, the cable is not involved.
Check your own manual before you plug anything in. Voltage, polarity and current draw differ from model to model, and the manufacturer’s figures take precedence over anything written here. A supply of the wrong polarity can damage a pedal in seconds, phantom power is safe for most microphones but not for every one, and the required voltage is printed next to the socket or stated in the manual — not inferred from a connector that happens to fit.
The questions players ask
Can a dimmer switch cause it?
Yes. Dimmers, chargers and some LED lighting inject noise into a mains circuit, and an amplifier on the same circuit can pick it up.
What if the hum appears only when the guitar is plugged in?
Then it is the guitar or the cable — single-coil pickups and long unbalanced cables are the usual explanation.
Last reviewed 2026-08-18