Re: TV and sound over CAT5

[Keith Doxey <keith.doxey@xxxxxxx>]

Hi Ray,

The signal you sent was from a reasonably low impedance source which is
less prone to interference than a higher impedance source, but the signal
you sent was still unbalanced.

The hum you heard was a mixture of induced mains hum and earth loop hum.
The difference between the two hifi's could be down to an earthed piece of
equipment such as Satellite reciever downstairs or simply due to the
difference in earth potentials between the mains sockets. The upstairs of
the house is almost certainly on a different ring main and even if it is
the same ring the sockets are physically closer together so will have less
difference in the earth potential.

You will definately notice an improvement by moving to balanced signals
either with a box of active electronics or with transformers although you
should be aware that the transformers themselves could pick up hum if not
properly sheilded and can also affect the frequency response of the signal.

Keith

Keith Doxey
http://www.btinternet.com/~krazy.keith
Krazy Keith's World of DIY Home Automation

-----Original Message-----
From:	Raymond [SMTP:Reb.barnett@xxxxxxx]
Sent:	Wednesday, July 28, 1999 10:06 AM
To:	'ukha_d@xxxxxxx'
Subject:	[ukha_d] Re: TV and sound over CAT5

<SNIP>
With regard to running audio over CAT5, I experimented a little last
night. I cut a short (screened) cable used for connecting portable CD
players to hifis in half and soldered 14m of CAT5 between the two ends.
<SNIP>
The upshot was that when run from the PC (upstairs) to our more
expensive hifi (downstairs), the sound quality was fine (as compared to
how it normally sounds, although I didn't perform a blind test ;-) ).
However, if I turned the gain up high (half way) on the hifi, to allow
me to control the volume from the PC, there was an unacceptable level of
hum (sounded like mains) when no audio was playing. Interestingly, when
connected to the upstairs hifi (a cheaper Aiwa), using the same length
of cable, there was a much reduced level of hum, to the point that it
was tolerable.
<SNIP>
Am I likely to see an improved by moving to a balanced signal?
(presumably yes). Do I do this simply by sticking a transformer at
either end of the 10base T cable?


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