Running Audio on Cat5 -- Possible???

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

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

 

First... I want to run two phone lines on the Cat5 -- which will

What you are seeking to do is possible, but how well it works will
vary.

If you simply RCA-terminate the two audio lines and go right into your
audio components, I predict horrible problems with crosstalk, and
especially with hum. You'll probably end up with a severe ground loop.

A better approach is to use a "balun" (balanced to unbalanced audio
transformer) at each end of each audio pair in the cable. A 1:1 audio
isolation transformer is really what you want... connect an
RCA-plug-terminated audio coax cable to one winding, and the RF-45
wire pair to the other winding. Using such a device will have two
effects:

- It'll prevent ground loops, by providing galvanic isolation of the
grounds in the two rooms. Ground currents can't flow across the
insulation between the transformer windings.

- It'll probably reduce hum and crosstalk, by using each twisted
pair in a fully-balanced mode.

You can buy commercial audio baluns (http://www.svideo.com/500019.html
is one such), or try homebrewing your own using audio isolation
transformers (e.g. Radio Shack #273-1374) and connectors and casing of
your own choosing.

 

It's possible. For line level signals, there will likely be
some discernable cross-talk, especially near the high
end of the audio range.

Not a problem unless you are driving speakers thru those
wires or hoping to get microphone input levels thru them
without some noise pickup.

Interference (aka "cross-talk") would be my only concern.

 

Possibly, but if your on the phone, you shouldn't be as worried about
the audio on the stereo.

 

What you want is entirely possible using a KAT5 transmitter and
receiver.

http://www.kat5.tv/index1.html

Although the KAT5 units are primarily for video, they convey an
audiophile-quality stereo signal. The wiring is as follows:

Blue (4&5) Left Audio
Orange (1&2) Composite Video/S-video Luma
Green (3&6) Right Audio
Brown (7&8) 2nd Video Circuit/S-video Chroma/Digital Audio

You can connect the audio pairs and leave the others unconnected. That's
what I do, and it works perfectly. Alternatively you could use SPDIF and
get *two* stereo signals down your two pairs.

I can't tell you about phone lines, but FWIW I have about 10 metres of
cat5 fixed wiring conveying KAT5 audio and ethernet in the same cable.
[To the structured wiring police: yes, I know, I know.] At each end
there's a specially-wired dual-RJ45 wallplate, with one outlet labelled
"LAN" and one labelled "Audio" going to the KAT5 unit. I've detected no
interference. To ask about phone lines you could contact Keith Doxey,
the KAT5 designer:

http://www.kat5.tv/contact.html

 

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.

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.

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.

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

 

I expect the 'phone circuits, now or in the near future, may be
carrying an ADSL carrier for broadband internet.

 

It'll be far from ideal anyway.

Or you could go a simpler route, and know that it will work, with
off the shelf components. Check out the exstreamer and instreamer
products from Barix.com. Very cool, interesting developer community
working on bolting them into various home automation systems.

All you need is normal CAT5 (or higher) plugged into your network
switch wherever you want to run audio.

 

I went the ready-made route and got two of these:

http://www.videocapturecard.com/svideobalun2.html

They transport the A/V from my PC across a distance of ~30 meters to a
stereo A/V modulator that merges the signal with my cable TV. It works
very well indeed.

Ximinez