sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging School Intercom system problem.

Recently I added a three 25/70 volt 15 watt Outdoor PA horns to an existing Dukane Starcall system.

I added three new 35 watt Radio Shack amplifiers due to the layout of the building and I didn't want to overload anything. All of the horns are tapped well below the max. I installed a Bogen adapter that reduces the line voltage (25/70 volts) from a speaker output from the Dukane system to a 600 ohm balanced output and used it for the input of my amps in the Tel/Aux input. I forget the Bogen part number but I can get it if needed.

Before I was called to add the horns another vendor added six 25/70 volt speakers in portable buildings near one of the horn locations. The teachers complained of low volume so I added them to the load on one of the new amps. All was fine until about a week ago and now I get no sound in any of the six classrooms which are on the same cable that feeds my horn. The horn still works and the cable is good going into the portables. When I put my toner on the wire at the splice where the horn is I can hear it faintly in all six rooms.
I've disconnected the horn and still nothing in the rooms.
I've tried connecting the room cables one at a time but nothing works.

Anyone ever see anything like this before?

You either have an open in one side of your feed wire or all the speakers are fried. You said you get a faint tone do you get continuity at the main splice? Have you tested a speaker to make sure they work ok they could have a damaged the voice coils

Thanks Merritt. We figured it out after removing all the room speakers.

It appears one room cable was going to ground on the Tip side and another room cable was grounded on the Ring side. Apparently the short wasn't enough to register with an ohm meter but the problem intensified when voltage was applied.

The only logical explanation for the horn still working I can come up with is that it's the first speaker on the loop. :shrug: