Earth loops

[Brian Gaff]

Just a word in case anyone has an idea here. I use a computer as a source on my hi fi, but when I plug in the monitor lead I get an earth loop. IE loud nasty buzzing on that input. the problem is a loop as unplugging the earthed items of the system apart from one, say, a mixer and the monitor, then it goes away as the only earth is then via the computer, or unearth the computer and earth the psu on the monitor etc, well you get the drift. Even unplugging a video lead from a set top box to the monitor reduces it. Now its really not safe to start unwiring 13amp maiins plugs earths, so I'm a bit out of ideas here.

Brian

[meow2222]

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

NT

[Andy Cap]

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

[John Williamson]

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.

[Bill Wright]

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

Bill

[Dave Plowman (News)]

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.

[Charles Fearnley]

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

are actually intended for telecom applications, and are speced at only

200 to 4k accordingly, but actually have a much wider freq response. I've used them in various applications similar to yours, and found them to be a sensible and low cost (£4ish) solution.

Charles F

[Brian Gaff]

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

[Brian Gaff]

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

Brian

[Andy Cap]

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

[meow2222]

madness!

NT

[Dave Plowman (News)]

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.

[tony sayer]

In article , Dave Plowman (News) scribeth thus

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

[tony sayer]

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;!...

RS have the Oxford electronic components range which are around a tenner each..

[meow2222]

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

[Dave Plowman (News)]

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.

[Charles Fearnley]

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]

"Charles Fearnley" wrote in message news:507ae010$0$1139$ [e-mail]...

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

[meow2222]

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

[tony sayer]

How exactly will you do that then?..