I'm searching all over for info, and someone here might be able to help me
get an answer or idea. A few companies are selling whole-house sound systems
that place standard line-level audio --unbalanced-- onto unshielded twisted
pair CAT-5e/6 cables. They (the manufacturers) say this works fine up to a
couple hundred feet.

I can't find any reason this should work. In fact, as I search the web for a
rationale, I fine lots of examples where balanced signals are used on CAT
5/6, which makes good sense. Using unshielded cable makes me wonder, but
that can wait a moment. I can't find anything anywhere that says unbalanced
audio is OK on UTP cable.

Does anybody know of some documentation on this subject, or do any of you
have any experience with unbalanced line-level on UTP?

-Thanks!

-John O
Heathkit Educational Systems
(yes, *that* Heathkit!)

John O wrote:
I'm searching all over for info, and someone here might be able to help me
get an answer or idea. A few companies are selling whole-house sound systems
that place standard line-level audio --unbalanced-- onto unshielded twisted
pair CAT-5e/6 cables. They (the manufacturers) say this works fine up to a
couple hundred feet.

I can't find any reason this should work. In fact, as I search the web for a
rationale, I fine lots of examples where balanced signals are used on CAT
5/6, which makes good sense. Using unshielded cable makes me wonder, but
that can wait a moment. I can't find anything anywhere that says unbalanced
audio is OK on UTP cable.

You run telephones for miles on that stuff. The reason telephones work is
that they have extremely good balancing on either side of the line, very
low line impedances, and good RF rejection on the front end, so that RF
trash can't get into any place where it will be demodulated. The secret to
this: transformers.

Does anybody know of some documentation on this subject, or do any of you
have any experience with unbalanced line-level on UTP?

Sure, I did a 6 mile run on a burglar alarm circuit from a radio station to
a transmitter for years until they modernized their STL. And I do occasionally
run line signals on existing dry telco circuits, using transformer isolation
on both sides of the line to get high CMRR. Without electrostatic shielding,
this is the secret to making long runs work.

-John O
Heathkit Educational Systems
(yes, *that* Heathkit!)

So are you the place I go to get replacement wafer switches for my SB-620
spectrum analyzer?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article writes:

I'm searching all over for info, and someone here might be able to help me
get an answer or idea. A few companies are selling whole-house sound systems
that place standard line-level audio --unbalanced-- onto unshielded twisted
pair CAT-5e/6 cables. They (the manufacturers) say this works fine up to a
couple hundred feet.

It probalby does, as long as you use those little bitty speakers that
don't reproduce anything below about 200 Hz. But hum is relative. And
if you're lucky enough not to have any serious current-carrying power
runs parallel to and close enough to the audio cable, you may not have
much of a problem. I doubt that they put transformers at each drop and
run the lines balanced, but that's possible. Again, if you're willing
to sacrafice some audio quality to cheap transformers (you don't think
a builder would use GOOD transformers, do you?) you wouldn't have a
problem.

Steve Lampen of Belden speaks highly of using Belden Mediatwist (a
high grade UTP Ethernet cable) for running balanced audio.

If you're fears are those of "unbalanced is high impedance and you'll
have high frequency loss with a long cable run" that isn't the case. I
suspect it's just a matter of getting away with it and knowing that
real audiophiles aren't going to use builder-installed cable unless
they specify what kind of cable to use - and it wouldn't be unshielded
cable for unbalanced runs.


--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

I doubt that they put transformers at each drop and
run the lines balanced, but that's possible. Again, if you're willing
to sacrafice some audio quality to cheap transformers (you don't think
a builder would use GOOD transformers, do you?) you wouldn't have a
problem.

Nope, one of each pair of signal lines is dead ground, common with the power
ground. This happens to be a low-end whole-house audio system (A-Bus) and
fidelity is not one of the primary features.

The better systems used balanced lines, but they still do unshielded cable
by default. I agree...if it were me the cables would be shielded no matter
what. In the end, these systems are not intended for high-end listening or
primary audio...they're for music in the rooms during a party, coming from
in-wall/ceiling speakers. Home-muzak, if you will.

Thanks for the insight, guys. :-)

-John O