I’ve got an old Goodmans amp, all it’s connected to is the speakers and a Sony CD player, but recently there has been a loud hum coming from the speakers whenever it’s on. The hum isn’t affected by the volume knob. I’ve tried disconnecting and reconnecting everything, and also had a look inside the amp – nothing obvious.

So is the amp dying?

Cheers 😉

also known as a ground loop

you need to do some fault finding testing – switching to other sources etc etc

Sounds like an earth problem, possibly? Check the earth on the plug, maybe a loose connection internally? I’m no electronisist, but a hum usually indicates earthing issues, or maybe a transformer.
You need an expert really… 😀

The amp isn’t earthed, which struck me as a bit odd too – it’s double-insulated according to the label on the back. There is a ground screw – worth connecting that to earth?

If its anything like my kef speakers it will be a capacitor somewhere.