Hi. I have a strange issue that is puzzling me.
I have my desktop PC hooked up to my stereo HiFi amp. When I am playing music or any audio, the quality is superb and it works perfectly with no audible hiss or hum or any kind of noise.
However approximately 4 seconds after the sound stops playing, such as the end of an album or when I press mute on the PC I get a very loud 50Hz hum.
The hum doesn't happen straight away, only after a few seconds, as if something is being switched???
I have this issue with the onboard sound card, a cheap USB soudn card, 2x creative soundblaster cards, an audigy card I borrowed. All exactly the same symptom. Work fine when playing, start humming when it stops.
I have tried using a stereo ground loop isolator. Which I as far as I understand is comprised of 2x 1:1 transformers so as to AC couple the signal like a DI box. However with the ground loop isolator the problem still exists so I do not expect it is a ground loop of any kind.
Does anyone know what might be causing this?
Thanks