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 Post subject: Suppressing hum
PostPosted: 12 Feb 2015, 23:05 
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My old Linux PC was getting very flaky and not worth repairing, so I'm temporarily using another old computer as my media PC, pending the arrival of a replacement. The snag is that I'm getting a lot of hum from the (analog) sound output to my amp, which I'm guessing is caused by a ground loop or something. The PC I'm getting has an optical output so this isn't a long term problem, but it won't be delivered for a few days. I really don't want to spend a ton of money to fix it since it's a short-term thing, so what I'm wondering is if a ground loop suppressor, as sold for car stereos, will do the trick. Anyone know? Or able to suggest a good alternative?
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 Post subject: Re: Suppressing hum
PostPosted: 16 Feb 2015, 16:06 
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Try changing the location of the power plug? I've heard that can help in some instances, maybe a different outlet. You can always check to see if its a ground loop. Hook up your old pc to a UPS or backup battery and unplug the ups.
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 Post subject: Re: Suppressing hum
PostPosted: 16 Feb 2015, 17:20 
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Yup, that's the first thing to try.

If you can get (or build with transformers) a cheap/quick ground loop isolator it's worth trying that, but since you're doing the real fix in a few days anyway, eh.
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 Post subject: Re: Suppressing hum
PostPosted: 16 Feb 2015, 17:59 
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Unfortunately all of the sockets are on the same extension block, so that wouldn't work. I didn't think of an isolating transformer for the power supply, I'm guessing that would work but it's a bit too expensive to be cost effective. I've ended up plugging in an old pair of computer speakers to bypass the amp completely, and that's done the trick.
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 Post subject: Re: Suppressing hum
PostPosted: 16 Feb 2015, 18:04 
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Cool :)

The other thing to get cheap someday would be a USB audio 'card' with optical out, they're not expensive and very easy to use.
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 Post subject: Re: Suppressing hum
PostPosted: 16 Feb 2015, 22:11 
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happycube wrote:
Cool :)

The other thing to get cheap someday would be a USB audio 'card' with optical out, they're not expensive and very easy to use.

The "new" computer (a 2006 Mac Mini) has optical out built in. The one I'm temporarily using will eventually going onto ebay, I think, so it'll be someone else's problem.

later - and I've just realised that you can get a USB to microphone / speakers adapter for a couple of pounds, that would have presumably worked too.

later - out of curiosity I tried one of the USB adapters - I think it uses the same earth as the PC, the hum is still there.
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