sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging loud humm

I have a weird problem with a paging system. I have a Panasonic switch which I am using an external page port to a bogen 60 wat amp over a 25 pair feed cable to an out building. I hooked everything up yesterday and all worked good till the next day when they came in the building the horns were humming so loud they had to un plug the amp. I checked the system port at the system and no humm but when I hook up to the 25 pair feed cable I get humm. I cant hear it at the system side but when I go to the amp side I hear it. I switches pairs and the same thing loud humm. Any suggestions?

It sounds like the amp is mounted in the out building and is being fed through the 25 pair - correct?

If this is the case, what happens when you disconnect the 25pr at the switch end but leave it connected at the amp end? I'm thinking ground loop.

When i dissconnect the system i still have a hum but it is not as loud as when it is pluged in to the system.

You didn't answer my question, I take it the amp is mounted in the out building?

If you are getting hum when you disconnect all inputs at the amp, you have a different problem. If the amp only hums when there are lines connected to the input, try the following:

-Are you using a 600ohm paging input on the amp? (reason I'm asking - this input would normally be through a built-in transformer which would isolate the amp from the phone system)

-You could try plugging the amp into another electrical outlet, trying to find one on the same electrical phase as the KSU. Keep in mind that it may be 3 phase hydro so it might take a few tries from different electrical outlets in different locations to find the same phase.

-Some amps have a ground jumper or strap between the GND and the COM terminal. You could try removing that.

-You can install an isolation transformer between the page port and the amp. Preferably a 1:1 ratio audio transformer.

It hums because it doesn't know the words? Sorry couldn't help it. :rolleyes: If you hear a little hum with it disconnect you're just amplifying the noise with the amp hooked up. All the things Twisted Pair points out, plus you may have AC power induction in the 25pr cable if it isn't grounded and that's what your hearing and amplifying.

You might also want to disconnect all of the wires going out to the speakers.
Sometimes you can get a ground from them as well because as has been suggested it sounds as if you have a ground coming from somewhere. Or maybe you have earth ground coming from more than one source and when everything is hooked up it magnifies the problem.

When you say you "hooked it all up" does that mean you are using existing cables and speakers, did you install a new amp, is the telephone system new?

If you can provide as much detail as possible as far as everything you have done I'm sure we will be able to help you.

TW,
if it Speaker with build in amp. you have to take off of external Amp. cause it picking up white noise and amplifies it. If this is regular Speaker you have to put matching transformers between Amp's output and Speaker or agjust output to lover level. That is all.