10 May
2009
10 May
'09
9:45 p.m.
On Sun, May 10, 2009 at 08:42:13AM -0700, Aaron L. wrote:
However, in the sense of diy (and there being some
great brains in this room),
I'd love to hear someones thoughts about this article.
http://www.mcmelectronics.com/content/en-US/diy/baluns
Scroll down to the yellow number 3.
Long unshielded transformer isolated twisted pair cable run for audio
... can work, but the things that would worry me are:
1. electromagnetic interference, or induced audio, ... at a gig I had a
twisted pair run parallel to speaker wire once and managed to induce
some crosstalk from the output back into the input, and the feedback
whistle was very different to audio air mediated feedback, and my mixing
position at the back of the building was not enough defense, ouch,
2. radiofrequency interference, you have a long antenna, ... probably
not a problem provided your equipment already has RF filtering, if
you've ever heard the GSM signalling from a nearby phone on your
equipment, then you know what I mean,
3. lightning strike, or telephone circuit fault current from a
neighbour ... you have your audio line running in the same sheath as a
telephone line, and the telephone line extends out of the house all the
way to wherever it is originated ... any lightning strike along that
path can raise the voltage on one pair in the sheath, which is harmless
to the other pair that you weren't using, since it is not terminated at
either end ... terminate it now to a transformer and the transformer
sits on the path to ground,
4. codes or regulations, ... some regulatory regimes prohibit this sort
of connection for various reasons, including safety of line workers ...
who dislike encountering strange voltages while buried up to their
ankles in mud next to an open cable termination ... ;-) while it should
not happen, it may, if the balun is faulty, or shorts, or is damaged by
a prior event that doesn't render it inoperative for audio.
--
James Cameron mailto:quozl@us.netrek.org http://quozl.netrek.org/