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#482863 08/25/11 01:18 PM
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I recently took on a new job at a school district. On the intercom systems where Valcom is installed, the original installers installed paging in the hallways of the schools using amplifiers wired for 25 volts. Why would anyone do this. I was thinking 7o volts was the normal. The paging sounds muffled at all locations. Also, they used the Aux input of the amp, instead of the telephone input for the Valcom system.

At 1 particular location, they installed a paging amp for one Zone, and self amplified speakers for another zone. I get a call today, and they reported that the zone the amp is on is bleeding onto the zone the self amplified speakers are on, causing the self amplified speakers to be broadcasting outside the school when the page was meant for inside.
When I looked at this I figured you shouldn't mix
self amplified speakers with speakers driven by an amplifier, or this could cause bleed over.

Am I correct, or am I missing something? Also, could the fact that all inside paging only speakers being on a 25 volt system and the amp connect to the aux port cause the muffle sound?


Gerald Ducote
NWA Telcom
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#482864 08/25/11 01:37 PM
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In some locales any wiring above 50 volts has to be in conduit, thus 25 volt gets around that requirement. You just tap the speakers differently on a 25 volt line.
I think most PA/intercom systems use 25 volts instead of 70.
Could be that the speakers are mis-tapped.


Jeff Moss

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#482865 08/25/11 02:03 PM
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Now after years of handyman workmanship and jury rigs a knowledgeable person steps into the position. I don't envy you your job!

#482866 08/25/11 02:05 PM
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25 volt is normal for school intercom partly because of the low voltage requirements as Jeff said and also because they don't need much power to each speaker. 1/4-1/2 watt is normal
The muffled could be either the amp is overloaded or an impedance mismatch on the input. You can run both a regular amp and self powered from the same source but you need to isolate both conductors of the signal from each other system so not to have bleed over.


Merritt

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#482867 08/25/11 03:12 PM
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What Jeff & Merritt said.

You're going to have to troubleshoot this. Do you have an impedance meter? It'll let you look at a run of speakers and see if the run is overloaded. If not you'll have to start from basics:

Disco all the speakers.
Hook up one speaker to one zone. Is it muffled or clean?
Add more speakers. Keep adding till you find the problem.
Start on the second zone.
Add one speaker. Are you getting bleed-through?

DO THIS ON T&M!!!! IT'S GOING TO TAKE A WHILE.

Sam


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#482868 08/25/11 04:16 PM
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Here in California 25volt is required for Schools.(don't want to shock the little bas*****).

#482869 08/25/11 11:20 PM
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K-Mart's were notorious for using 25 volts. The bad news was those systems don't take to kindly to employees "adding a speaker". You can usually tell that because you can fry an egg on the amp. They just keep on turning up the volume while the amp works its heart out to compensate for the 8 ohm load across the speaker line.

The only mistake I made was learning the reason you don't put your Mic cable in the same run as the speaker line. Probably the same reason you don't put Valcom amplified speakers in the same run as your speaker lines.... Fortunately I only did it once :-)

Carl


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#482870 08/26/11 09:23 AM
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If all else fails, use a relay to short the Valcom speech path, or power down the Valcom 24 Volt power when they're supposed to be silent.

As for the muffled sound, you have either got an overloaded amplifier, 1 or more 4-16 ohm speakers without 25 volt transformers, one or more bad speakers, or a 'tired' amplifier. In any case, you'll want to do an eyes on inspection and test of each 25 volt speaker.

As SAM said, T & M ONLY!!!! And the Impedance Meter will save you HOURS, or even DAYS.

One more possibility. I have seen neophytes try to use the 25 volt line power to power Valcom speakers! NO, IT WON'T WORK. If you're lucky there won't be any damage.


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#482871 08/26/11 03:36 PM
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The Valcom and 25 volt speakers can share a common audio source but cannot share a common power source. First I would make sure all the Valcoms are working correctly with one pair coming from the 24 volt power supply that is large enough to power the number of speakers you have. That is the biggest mistake that is made, a power supply that doesn't have enough units to power all the speakers. When connecting a 70 volt source to Valcom paging you should use PN v-1095. This single gang expansion module allows a Valcom system to be connected anywhere on 25/70/100 volt line without straining the the existing amp.


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#482872 08/29/11 07:34 AM
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Turns out the bleed over on the valcom self amplified speakers was caused by the background music option being turned on on the valcm intercom system, and no background music source installed. I turned it off, and no more bleed over.

Thanks for all your advice on troubleshooting, and 25 volt paging. I'm still working on the muffled problem.


Gerald Ducote
NWA Telcom
[email protected]
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