Newsgroups: rec.audio.tech
Subject: Re: Long interconnects
References: <[email protected]>  <[email protected]>  <[email protected]>
Dave Crawford  writes:

> Richard Crowley wrote:
> > 
> > "Dave Crawford" wrote ...
> > > Construction was completed years before anybody heard of home theater,
> > > and there is no way to pull wires through the walls. I can at least
> > > adequately camouflage a CAT-5 running from one end of the room to the
> > > other. I'm looking at running line level from the HT receiver in the
> > > front to a separate power amp in the rear, powering the surrounds. I
> > > haven't been able to come up with a way to adequately hide 4 pair of
> > > speaker wires.
> > 
> > Several vendors (including some that specialize in HT) sell balun
> > transformers that allow you to run line-level audio over CAT-5.  Or are you
> > asking for an alternative to that method for some reason?
> > 
> 
> I thought of this potential solution because some of the DIY audiophile
> interconnects use a single pair from a CAT-5. They don't use a balun. 

That's true. This kind of interconnections are not good.
They could be better in carrying the audio signal itself (lower
capacitance than other cables if that matters), but they have
a poor interference protection (pick up neasily noise and RFI).
If you use this kind of cable for HiFi system, it is no
woder if radio interference is problematic and all kinds of tricks
might change the sound (poor shielding makis noise picking easy,
when wires are moved noise changes...)

CAT-5 twisted pair has very good noise immunity when used
to carry signals in balance manner. But if you use it
to carry unbalanced signals, most the good noise immunity
is immediatly lost, and this wire is not much better 
than any "unshielded cable".

To properly run audio through any considerable length of
unshielded twisted pair wiring (CAT-5 or other), the audio
needs to be balanced (balancing + twisted pair = good noise immunity
agains external noise and between pairs).
For the audio to be balanced, the equipments on the both ends
need to have balanced audio interfaces (usually XLR connectors)
or you need to do unbalanced-balanced conversion on both ends
of a cable (audio transformer can do this).

> It seems like an audio frequency balun would be rather large. Can you point
> me to one? 

Take a look at the following pages:
http://www.epanorama.net/documents/groundloop/audio_isolators.html
http://www.epanorama.net/documents/groundloop/audio_isolator_building.html

> I don't have "golden ears", and this is for the surround
> channels, so I thought maybe I could use all the pairs to make one long
> set of 4 interconnects to get the line level signal from one end of the
> room to the other.

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