Earth loops

Earth the computer, and connect the other appliance earth wires to the pc case isntead

NT

Look for a hi-fi isolation transformer and connect it via that. They're available on Ebay and many other good outlets ! You'll need to insert phono plugs in both left and right sides, but it saves mesing about with the electrics.

Andy C

An isolation transformer in each audio path between the computer and the Hi-fi will definitely do it. They can be bought from just about any pro audio supplier. They may be sold as a ground lifter.

Other than that, you need to use a star earthing system, with all the earth connections on the Hi-fi and computer system going directly to a single point. Something like plugging everything into extension strips all connected to the same socket might help. It might even be something as daft as a loose earth wire on the ring main between the sockets you're using, or the two sockets you're using being on two different rings.

Can you just plug all the mains plugs into one of those six-way or eight-way sockets?

Bill

Easiest solution is an audio isolation transformer (one per channel) between computer and amp - removes the DC path from the audio.

They're often needed on car sound systems where an external amp or two is needed so a place that sells those should have them - or Ebay, of course.

A suggestion for suitable transformers are these ones from Rapid, and CPC have similar too.

Charles F

I'd presumably need one for input and one for output on the puter though. I'm thinking the biggest hum increase is always when I connect the monitor lead, and the hum goes higher in frequency as well, so I'm wondering if it might not be being induced from the signals for the monitor. I need to have a think about this. Brian

Already done that and it made no difference, except that it took me half a day to disentangle them all etc.. grin.

Brian

Not quite sure what you're trying to do. I play stuff from the PC into an amp and used to suffer the same hum but putting an isolation transformer in the lead eliminated it completely. If you're also trying to import a signal from the amp into the PC, then yes, I guess you'd need to break that too, else you've got the same earth loop in place.

Andy C

madness!

NT

What do you mean? Laptops are hardly going to have the highest of fi audio circuits and these transformers can be perfectly ok. They are cheap because they are made in huge quantities.

In article , Dave Plowman (News) scribeth thus

You might try an external USB connected sound card that sometimes can eliminate humm loop problems...

Well not that good for audio. If you do decide transformer isolation is the way to go then there are better ones that don't cost that much more;!...

There is a far cheaper simpler and better quality way to do it. A phone tra= nsformer with freq response down to 300Hz and up to who knows what is an aw= ful solution. Laptop line level output spec is far beyond such things.

You can of course do all sorts, I've even used mains transformers for audio= . But a far better simpler cheaper quicker solution exists.

NT

That is only saying it meets the spec for telephone lines. As was said they considerably exceed it. If you want a decent repcoil specifically made for high quality audio, expect to pay many times that amount.

And a mains isolation transformer costs what? Talk about taking a sledgehammer to crack a nut.

Well, everybody is right that you can get better audio transformers at higher prices than the Rapid telecom ones mentioned.

In a previous life I was part of the sound staff at one of the big five ITV companies, and as a sideline made an assortment of small talkback/communications gear for them, when the real maintenance dpt couldn't be bothered with the hassle of one offs and very short runs. I used the transformers mentioned to balance audio inputs and outputs, as a cost effective solution, as I needed a lot of them. I was getting -3db points at around 50hz and 18khz - not quite hi-fi, but perfectly adequate, and the gear sounded very clean. No one ever complained!

Since then I have balanced PC's in and out with these too, and they work ( and sound) fine.

Thanks to Dave P for your sensible support!

Charles F

"Charles Fearnley" wrote in message news:507ae010$0$1139$ snipped-for-privacy@news.zen.co.uk...

Final thought - to make their use entirely clear - I would (obviously) NOT put these in a broadcast audio chain, but for general use they can be very useful, and cheap enough to have a few in the spares box.

Charles F

It may much exceed it at the high end, but it won't at the low, doing so would be a waste or iron & money.

Indeed. Be sensible and reroute the mains earth, like every class I separates hifi system does.

NT

How exactly will you do that then?..