Newsgroups: rec.audio.tech
Subject: Re: Sound out from computer to receiver - hum is heard!
References:    <%[email protected]>  
"LarryLOOK"  writes:

> > If the ground loop problem is the reason, then generally the
> > problem does not go away by using external USB audio device
> > with line output. Both on the USB audio adapters and the PC
> > soundcards (all I know this type of devices) the audio
> > output ground is connected to PC case ground
> > (which gets connected to mains ground through power
> > lead ground pin). In this kind of connection both
> > internal sound card and USB device would make the noise.
> >
> > Generally the best way to get rid of ground loop problem is to
> > isolate the audio signal using audio isolation transformer.
> > This gets rid of the grounding related noise.
> > Usually this is done using external audio isolator adapter
> 
> Not sure how to buy or use an external audio isolater adapter.  Is this 
> complex and/or expensive? I'd prefer not to have to go into the computer and 
> mess around if I don't have to - I'm afraid I'll do more harm than good. 
> Can you send me a link to this device?

Audio isolator adapter is very simple to use device if you get 
right kind of device. Those typically are just a small box 
/made of plastic or metal). There are two cable pairs coming 
out of it. One is terminated to two RCA make connectors and other 
is terminated with two RCA female connectors. 
Intallation is simple: Just put this device between your cable 
coming form computer and your amplifier. So just diconnect computer 
cable RCA connectors form amplifier, plug in RCA connectors from 
audio isolator to amplifier inputs and plug the RCA connectors 
from computer audio cable to free RCA male connectors on the isolator. 
Now thigns should work nicely and without noise. 
You can fidn picture of one device I have used at 
http://www.biltema.fi/osteri/data/Kuvat/31_441iso.jpg

This product is sold in Finland for little less than 10 Euros
http://www.biltema.fi/osteri/osteri.cgi?sivu=skriptisivut/index_kauppa.htm&linkki=31441.htm&tuote=31441&ryhmaid=30
I have used this successfully to solve this kind of ground 
loop problems many times. 

There are links to some other commecially available products at 
the end of the web page at 
http://www.epanorama.net/documents/groundloop/audio_isolators.html
(those links are for all kinds of isolators, one with RCA 
connectors and also other ones with different connectors that 
might not be directly suitable ot you).

> > (theoretically this function could be built into USB audio
> > device or PC soundcards, but I don't know any product that does this).
> > If you can make the connection using optical digital
> > interface, that connection will carry sound as well
> > without noise.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/