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Author Topic: High pitched buzzing in 25 volt paging system  (Read 746 times)

Roger Rhea

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High pitched buzzing in 25 volt paging system
« on: May 04, 2018, 08:36:18 am »

First off, new to the forum and looking forward to the vast information provided here.

I work for a telecom company and we often install paging systems for our customers. We use Valcom exclusively due to the ease of utilizing twisted pair cabling. That said, I recently replaced a Telecor 25 volt system with a Valcom Class Connections system. In addition to the existing 25 volt talkback and one way speakers we also installed several Valcom ceiling speakers for additional coverage in hallways. Everything was fine at first but now I'm getting a high pitched buzz through the one way 25 volt speakers and horns. It doesn't affect the one way Valcom speaker or the 25 volt talkback speakers. The one way 25 volt speakers and horns are powered by a 200 watt 2 channel amp to a 25 volt transformer and then to the speakers and horns. I thought I found the problem via a grounding issue as it went away for about 2 days but returned. This is a barely audible, (to a 64 year old installer) buzz but can be readily heard by the teenagers in the high school. I haven't isolated wiring yet but figure that's the next step. The original Telcor system either took a power hit or storm damage.

Thanks for any help!
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Roger Rhea

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Re: High pitched buzzing in 25 volt paging system
« Reply #1 on: May 04, 2018, 02:46:36 pm »

First off, new to the forum and looking forward to the vast information provided here.

I work for a telecom company and we often install paging systems for our customers. We use Valcom exclusively due to the ease of utilizing twisted pair cabling. That said, I recently replaced a Telecor 25 volt system with a Valcom Class Connections system. In addition to the existing 25 volt talkback and one way speakers we also installed several Valcom ceiling speakers for additional coverage in hallways. Everything was fine at first but now I'm getting a high pitched buzz through the one way 25 volt speakers and horns. It doesn't affect the one way Valcom speaker or the 25 volt talkback speakers. The one way 25 volt speakers and horns are powered by a 200 watt 2 channel amp to a 25 volt transformer and then to the speakers and horns. I thought I found the problem via a grounding issue as it went away for about 2 days but returned. This is a barely audible, (to a 64 year old installer) buzz but can be readily heard by the teenagers in the high school. I haven't isolated wiring yet but figure that's the next step. The original Telcor system either took a power hit or storm damage.

Thanks for any help!

Back onsite today and connected a 25 volt one way speaker at the system itself and still had the buzzing. Long story short it appears we have a ground loop. I have ordered a couple of ground loop isolation units, one for each of the 2 channels on the amp. This should clear up the problem.
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Scott Holtzman

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Re: High pitched buzzing in 25 volt paging system
« Reply #2 on: May 04, 2018, 03:31:19 pm »

Back onsite today and connected a 25 volt one way speaker at the system itself and still had the buzzing. Long story short it appears we have a ground loop. I have ordered a couple of ground loop isolation units, one for each of the 2 channels on the amp. This should clear up the problem.

God forbid we should actually fix the issue before putting something else in on the signal chain.

Sorry this is one of my pet peeves.

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Scott AKA "Skyking" Holtzman
River Delta Audio is now:

Ghost Audio Visual Solutions, LLC
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www.ghostav.rocks

Jean-Pierre Coetzee

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Re: High pitched buzzing in 25 volt paging system
« Reply #3 on: May 07, 2018, 11:29:17 am »

High pitched buzzing that teenagers hear but not a 65 year old. I would see that as a sign of potential equipment failure rather than a ground loop.

Any ground loop should be at most like a 7th harmonic of your mains frequency and the 7th harmonic should be the softest of them not the loudest(ok maybe 13th but then I doubt it would be that loud compared to the massive 50/100 60/120 Hz hum you will have)
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Hal Bissinger/COMSYSTEC

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Re: High pitched buzzing in 25 volt paging system
« Reply #4 on: May 09, 2018, 10:22:19 pm »

Quote
The one way 25 volt speakers and horns are powered by a 200 watt 2 channel amp to a 25 volt transformer and then to the speakers and horns.

Tell me more about that two channel 200w amp, the 25v transformer and how it's connected.

-Hal
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