klem kedidelhopper wrote:

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


If the level is right, I would add a 12 volt relay to connect the audio
to the amp when the siren is on. It sounds like the level to that mic
input is way too hot. You say, 70 volt, but not the wattage so I can't
calculate the turns ratio. You also don't state the output level from
that siren driver. From working with alarms back 40 years ago, the
drivers were a minimum of 5 watts, and some were close to 45 watts. You
could be feeding several volts to that mic input when the siren goes,
and it may destroy the transistor or IC for that input. I always used a
pot after the transformer to set the maximum level. I used to make promo
tapes for Cinemax, HBO and other CATV channels and mail them out to
radio stations each month. They were recorded of C-band and the only
place to get the audio was from the external speaker jack on the
monitor. I put a 10 ohm resistor across the input, and used a 10K pot to
set level. No one ever complained about the audio quality.