Hum has a short list of causes and each sounds slightly different. Ten minutes of unplugging things usually finds it.
The isolation test
Volume at a normal listening level, nothing playing. Still humming with no source connected? Stop there; the amp itself needs a technician. Otherwise reconnect your sources one at a time, TV first, then the computer, the streamer, the turntable. The connection that makes the hum appear is the guilty pair: those two devices disagree about earth, and the difference rides your audio cable as a 100 Hz tone (in Europe; 120 Hz in the US).
Fixes, cheapest first
- Plug both offenders into the same power strip.
- Cable or satellite TV is the classic source. A coax ground isolator on the antenna line costs around €30 and ends it.
- A buzz that changes when you move a dimmer is the dimmer. Replace it, or put the amp's power on another circuit.
- Noise that shows up with a computer is usually dirty USB power. A powered hub or a proper audio interface cleans it up.
Whatever you find: never "fix" a hum by removing a power plug's ground pin or cutting the third prong off. That pin is there to trip the breaker if something faults, and defeating it turns a nuisance into a shock hazard.
If it's the turntable
Hum that only appears with the turntable selected is usually the ground wire. Connect the thin wire from the turntable, or its phono stage, to the GND terminal on the amp. While you're back there, check that the plugs are fully seated; a half-inserted plug picks up everything.
Telling hum from buzz
A pure, steady low tone points at grounding. A gritty, rasping buzz points at dimmers, switch-mode power supplies or fluorescent lighting nearby. Knowing which one you have halves the search.