Noisy sound system automatic power-off.

[ghorizo]

Hello, please help me with this little problem of mine.
I find myself with a rather noisy surround system producing a hum particularly noticeable when no music is playing.
I was wondering if it would be possible to insert a relay after the main switch that turns on when power is detected on the line-in or would that mean lots of isolation circuitry? Can't seem to find anything of the sort.
Otherwise I thought of having the computer control the relay whenever something is playing with a usb relay board.
What do you think?

[NiHaoMike]

Try using a digital input on the amplifier if there is one?

[ghorizo]

Sadly no digital input, it's quite a cheap little 5.1 surround. The cables aren't even detachable from the unit. At least the subwoofer features connectors.
Probably not worth dealing with for many but it sort of works, and since I have some relays  around, I hoped it would not be too difficult but I don't know much.

[NiHaoMike]

Turn the volume on the PC all the way up (or slightly less if it starts clipping) and turn down the volume on the amplifier.

[ghorizo]

Had tried that at the beginning but even if I turn the ampifier way down to zero the sound from the speakers remains always constant.

[themadhippy]

sound/vox  operated switches were a fairly common project in magazines several moons ago,and google search for "sound operated switch turns up plenty of circuits" .Do be aware  youll miss the first bit of the audio and you need to have the hold on delay time long enough so its not turning off during any silent passages

[NiHaoMike]

Had tried that at the beginning but even if I turn the ampifier way down to zero the sound from the speakers remains always constant.

That means the amplifier itself is junk, you could replace it with a better one - try your local Goodwill or similar if you want something cheap, specifically look for ones that have S/PDIF but no HDMI or those that have HDMI but no 4K passthrough for some nice deals. Or you can try connecting power resistors in series with the speakers to increase the usable SNR, experiment with lower powered resistors with nothing playing to find out what minimum value gets the noise to tolerable levels.

The more advanced hackers can start reverse engineering the amplifier and try to redesign it for better SNR. If you can provide pictures of the boards inside, we might be able to suggest reasonably simple mods.