Newsgroups: rec.audio.tech,comp.home.automation,sci.electronics.basics
Subject: Re: Running Audio on Cat5 -- Possible???
References: <[email protected]>
"Ringo Langly"  writes:

> Hi all,
> 
> I'm looking at wiring up my home with Cat5, and I have some rather odd
> questions.  First every room will be wired with two pairs of Cat5 cable
> -- one definately for ethernet but the other I'd like to keep open for
> other applications, which is the purpose of this email.
> 
> First...  I want to run two phone lines on the Cat5 -- which will
> eat-up two pairs and leaves me 2 more pairs.  Is it possible to run
> audio over those other two pairs?  By audio, I mean wire-up a standard
> Left and Right (RCA) jack to either pair for stereo audio.  Is this
> possible?  

It is possible to run normal line level audio signals through 
CAT5 wiring together with other signals. I have personally 
done this, typically with video signal on the same cable. 
But there shoudl not be any problem with telephone on the same 
wire either (some crosstalk from rign signal and pulse dial possible). 

There is on "secret" on running the audio signal through CAT5 wiring 
successfully: the signals must be balanced. 
Balanced signals can be transported nicely through twisted pair 
cables without considerable crosstalk or without picking much 
noise on the way. The CAT5 twistred pair cable is not a suitable 
medium for transporting unbalalanced audio signals (the 
signal transfer method used n consumer audio RCA connectors and such). 
If you wire unbalanced signal source to CAT5 UTP, you will 
get considerable crosstalk between the signals on different pairs 
and the signal will very easily pick up humming noise. 

Balanced signals are available directly from professional audio 
equipment and can be directly wired to CAT5 UTP. One audio 
signal takes one wire pair. For left and right audio you need two 
wire pairs. 
If you want to connect equipment that do not have balanced 
connections on them, you need to use audio transformers on the 
both ends of the CAT5 UTP cable to perform balanced-unbalanced 
conversion (from unbalanced RCA to balanced on signal source end and and 
back from balanaced to unbalanced in the receiving end). 
In addition to signal balancing such tranformers will provide 
galvanic isolation on the audio interconenction 
(without isolation many times conenctions from one room 
to another will pick up humming noise). 
Ground currents can't flow across the insulation between 
the transformer windings. 
Audio transformers are available as separate components 
and there are also commecially adapters that can convert 
RCA audio to CAT5 wiring and back. 

> I'll have a patch panel each cable will run to, so wiring-up
> some audio cables shouldn't be too difficult.  

You need to wire those audio transforemers to your circuit as well 
between your RCA and wire on the wall. You just can't just patch-in 
the cable from the hifi equipment to your patch panel. 

> I'm just technically not
> sure if audio will even run over a small gauge of wires for this length
> -- which I'm looking at 50-60 feet.  

Line level audio will run though this wire this distance quite well. 
Been there, done that. I have one system at my home where I run 
the audio and video trough CAT5e wiring from my computer room 
to my living room TV/hifi system. Cabling distance is about 15 meters. 
No problems. The adapters are homebuilt (my own design). 
The audio adapter part is built out of one of those RCA stereo audio 
signal isolators sold or solving ground loop problems. 
Basicly have opened one the device (it includes two audio transformr), 
cut out the original signal out cable, disconnected the audio 
transformer secondaries from original wiring completely and 
soldered to two pairs on the CAT5 wiring. Works very well, 
is easy to build (if you know how to solder), and cost 
is very reasonable (those RCA isolators cost around 10-20 USD). 
Just build two of theose adapters, one for each end of the connection. 
Or go to a shot and buy a ready made box at considerably higher price.

> Also I'm not sure if there'll be
> interference with two phone lines and two sets of audio cables running
> through the same Cat5 cable -- given the cables can support the audio.

There is potential for some interference, but it could work 
well acceptably for you. 

> Thanks in advance for any ideas or suggestions.  I'm just trying to
> make wiring my home both easier and as simple as possible.  Take care,
> Ringo



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