On Feb 18, 12:10*pm, "Michael A. Terrell"
wrote:
klem kedidelhopper wrote:

To further explain this, the amplifier's, (which is located in one
building), output is taken off the 70 V tap, however as Phil alluded
to the voltage on the line could be and in fact in this case is very
low, ,just a few volts. This is all I need because, again this is VERY
low background music and the level seems to be satisfactory throughout
the building. As far as the lines being balanced, I'm assuming that
they still are as I have done nothing anywhere that I can think of to
cause an unbalance.

* *Old cable can have a conductor shorted to ground somewhere. I've
found wire with badly abraded jacket laying on steel beams, or nicked on
the corner of an electrical box.

As I mentioned before this balanced line output
leaves the amp on two pairs of a CAT3 cable. I used two pairs because
they are the main feed for all the speakers. This "main" cable runs
from this building underground through PVC pipe to the 66 block in the
other building. At that location all the other CAT3 wires also appear
on that block as well. On each cable that was reused the brown pair is
connected to a speaker. in a different room. These brown pairs are all
placed in parallel and then connected to the 70V feed. So this is all
well. It is not however the problem. The problem is occurring when I
try to sample the siren driver output from the alarm and apply it to
the low level input of the music amplifier. That's when I hear the
data noise which I'm certain is being picked up by the "antenna" which
is the sample wire and fed into the mic input of the amplifier.

* *Is that "Siren driver output" the actual speaker connection, or DC to
power the sirens? *Is the connection isolated by a transformer?

When the alarm is activated, 12VDC is applied to the "siren driver".
The driver outputs a "whoop whoop" sound to an 8 ohm speaker. The
speaker is located in a different building than the alarm system. The
CAT3 cable to the speaker is punched down onto a 66 block near the
alarm system control box. This cable serves two functions. It sends
the siren driver output to the speaker, and also by cross connecting
another of it's pairs on the 66 block also sends the siren driver
output back to the PA amp where I connected it to the 70V transformer
primary and then connected the 45 ohm secondary to the mic input.
That's when I heard the "ticking" or "fluttering" noise. I really do
think that the cables are physically in good shape. Lenny