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Posted By: NWA Telcom 25 volt paging? - 08/25/11 05:18 PM
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?
Posted By: jeffmoss26 Re: 25 volt paging? - 08/25/11 05:37 PM
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.
Posted By: jwooten Re: 25 volt paging? - 08/25/11 06:03 PM
Now after years of handyman workmanship and jury rigs a knowledgeable person steps into the position. I don't envy you your job!
Posted By: metelcom Re: 25 volt paging? - 08/25/11 06:05 PM
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.
Posted By: Silversam Re: 25 volt paging? - 08/25/11 07:12 PM
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
Posted By: Jim Baldwin Re: 25 volt paging? - 08/25/11 08:16 PM
Here in California 25volt is required for Schools.(don't want to shock the little bas*****).
Posted By: Carl Navarro Re: 25 volt paging? - 08/26/11 03:20 AM
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
Posted By: Lightning horse Re: 25 volt paging? - 08/26/11 01:23 PM
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.
Posted By: Derrick Re: 25 volt paging? - 08/26/11 07:36 PM
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.
Posted By: NWA Telcom Re: 25 volt paging? - 08/29/11 11:34 AM
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.
Posted By: Silversam Re: 25 volt paging? - 08/30/11 05:42 AM
Quote
Originally posted by NWA Telcom:
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.
That's something I should have mentioned. Open inputs look for signal. If they don't have one of their own they'll hunt down someone else's.

Good catch. Keep working on the muffling. You'll get it.

Sam
Posted By: Owain Re: 25 volt paging? - 09/01/11 01:01 AM
Quote
Originally posted by Jim Baldwin:
Here in California 25volt is required for Schools.(don't want to shock the little bas*****).
Here in UK we just use 100V for audio mad
Posted By: Silversam Re: 25 volt paging? - 09/01/11 05:28 AM
Quote
Originally posted by Owain:
Quote
Originally posted by Jim Baldwin:
[b] Here in California 25volt is required for Schools.(don't want to shock the little bas*****).
Here in UK we just use 100V for audio mad [/b]
Yes, but you also use 240v for "standard" electrical service (which is much better then 120- but tthat's another thread).

I did a job for a British Company with offices here in NYC. The PA was spec'd by the home office and the equipment was 100V. Interestingly, the transformers had taps on them for 200V too!

Sam
Posted By: Owain Re: 25 volt paging? - 09/11/11 10:01 AM
Quote
Originally posted by Silversam:


I did a job for a British Company with offices here in NYC. The PA was spec'd by the home office and the equipment was 100V. Interestingly, the transformers had taps on them for 200V too!

Sam
I've never seen 200V used at the speakers but it's possible the 200V amp output was used for large installations such as Radio Butlins holiday camps, and there was a 200V-100V transformer closer to each speaker cluster or line of 'chalets'.

Hi-de-Hi!
Posted By: Renn Re: 25 volt paging? - 09/20/11 05:38 AM
Quote
Originally posted by NWA Telcom:
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?
Posted By: Renn Re: 25 volt paging? - 09/20/11 05:43 AM
I came across this site while trying to find someone that could help with my problem. I work for a K-12 school in Cincinnati. Six years ago we constructed a new building and had someone install a Valcom paging system. This was one of those (side jobs) by a cabling guy. Apparently he didn't know what he was doing because it has never worked properly. Every time it rains, the system does not work. It doesn't perform the "all call" function and any announcements made are filled with static. I have had a few companies come in and none have been able to identify the problem. I don't know what to do. We rely heavily on that system. Do any of you know of anyone in the greater Cincinnati area that knows how to work on a Valcom system? We do not have anyone on staff that understands the system. HELP!
Posted By: Owain Re: 25 volt paging? - 10/04/11 03:07 PM
Quote
Originally posted by Renn:
Apparently he didn't know what he was doing because it has never worked properly. Every time it rains, the system does not work.
well, you've obviously got cabling faults and water ingress. Go right back to the start and sketch out a diagram of every piece of equipment and length of cable. Disconnect every piece of equipment; test amplifiers etc on the test bench, test speakers in situ with a local (battery powered) test amp.

Megger every length of cable core-core and core-earth for insulation faults, shorts and open circuits.

Then reinstall the workinbg equipments in sections, working to the manufacturer's instructions, testing as you go.
https://www.valcom.com/techsupport/knowledge.htm
Posted By: jeffmoss26 Re: 25 volt paging? - 10/04/11 06:01 PM
Renn, PM sent.
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