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25volt vs 70volt
#633331 10/17/19 01:31 AM
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I’m pretty familiar with 70 volt paging Systems
Basically you would use a 70v for long distances multiple speakers on the same zone

Occasionally I run into a situation where they using 25V

I was just wondering why somebody would use a 25v

I thought it might have something to do with talkback speakers

Anyways I have a school that they want me to correct some of the paging issues that they have
it’s wired using speaker wire and telephone wire The building is pretty tough to Run Cable in
The speakers seem to be all set at 25v
They are using a 35 W amplifier In one building and 100 W amplifier for the other building

The building that is having the issue which varies daily
Has really low ceilings 6 foot high in the hallways I think there’s just one speaker in each hallway and One speaker in each classroom
the classrooms are a little higher ceilings than the hallways when people walk by it they can hear the white noise (Power) coming out of the speaker

This is all Bogen wall baffles I think that they are tap too high
And I don’t believe there’s any volume controls on them


Any thoughts would be greatly appreciated

Thanks

JD

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Re: 25volt vs 70volt
teldata1 #633332 10/17/19 02:26 AM
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Ouch. Telephone wire for paging speakers is never a good idea except when using self amplified speakers. As for 70v vs 25v - this has been discussed in the past. Do a search if you really want to know more. I only use 70v as this is what I was taught almost 40 years ago from a company that specialized in large paging systems. Basically, 25v shouldn't be used outside of a very small installation and even then, I ask, Why? Of course, this doesn't address your speaker hiss but I tend to use relays when that is an issue. Since you probably won't replace the twisted pair wiring, try grounding the unused pairs.


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Re: 25volt vs 70volt
teldata1 #633334 10/17/19 02:34 AM
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Apparently, some regulations require 25V in schools because someone somewhere in California thinks 70V is dangerous to the kids. Go figure...

https://sundance-communications.com/forum/ubbthreads.php/ubb/showflat/Number/483169/Searchpage/2/Main/70050/Words/%2B25V/Search/true/re-25-volt-paging#Post483169


- Dave S. -

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Re: 25volt vs 70volt
teldata1 #633335 10/17/19 04:21 AM
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Well, don't know about California because I don't even want to know it exists. But the 25 volt system came about because there were (or are) some codes or requirements that require any voltage greater than 50V to be Class 1 wiring- that means the same type of wiring used for lighting and power. Out of those, for 70 volt speaker wiring your options are conduit or MC cable in those jurisdictions.

HOWEVER nearly all 70 volt amps today regardless of power only require CL2 wiring which can be regular speaker wire but we prefer to use something better. Unfortunately in those jurisdictions above I believe they still want it in conduit or MC cable.

If you think that's bad, would you believe Chicago requires all homes to be wired with all the wiring in conduit?

Quote
... when people walk by it they can hear the white noise (Power) coming out of the speaker


Power? grin That's hiss and could only come from the amp or its source. Could be the amp is turned up way too high to compensate for an input that's way too low or there is a noisy component in it and it needs repair. Could be the hiss is coming from before the amp- whatever it gets its audio from. Turn the input level and the master level down one at a time and see what happens.

Nothing to do with the speakers being tapped too high.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
Re: 25volt vs 70volt
teldata1 #633339 10/17/19 02:29 PM
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You can also remove the input sources and see if the hiss goes away. If it does it is probably an input source. Couple of ways to deal with that, my favorite being an isolation transformer.


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Re: 25volt vs 70volt
Daniel #633340 10/17/19 04:15 PM
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Originally Posted by Daniel
You can also remove the input sources and see if the hiss goes away. If it does it is probably an input source. Couple of ways to deal with that, my favorite being an isolation transformer.


Isolation transformer? For hum maybe- if it's because of a ground loop. But hiss is usually generated within equipment and no isolation transformer is going to help that. Good idea disconnecting the input source to see where it's coming from though.

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
Re: 25volt vs 70volt
teldata1 #633404 10/22/19 05:36 PM
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Ok

so I just did a site survey on the external paging system in one of the 2 building which has a 35 watt bogen amplifier the other building has a 100 watt speaker


They are using Toshiba phone system and they can page each building separately

all of the speakers are the wood grain wall baffles with volume controls

we have

19 speakers tapped at 4 watts

and several others that add up to 9 watts


for a total of 85 watts


There is also a 8 ohm speaker on the system as well

they are using the 25 volt on the amplifier

there are several rooms that don't have speakers that will need them but I was also wondering if they wanted to have the page go thru the phone



my question is how is this working I thought that you shouldn't go over the wattage of the Amp been installed for years


Re: 25volt vs 70volt
teldata1 #633409 10/22/19 06:40 PM
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You shouldn't go over the wattage of the amp. If the wood grain speakers with wall baffles are turned down far enough they would have a low enough wattage to not put the amp into protection. Not sure what the 8 ohm speaker is doing, or how it is working. (unless they are pulling some shenanigans with volts, ohms, and watts). You could possibly chain out of the amp, to another amp to run the new speakers leaving the old stuff alone. You could also put an amp in capable of running all of the things old and new.


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Re: 25volt vs 70volt
teldata1 #633420 10/22/19 10:30 PM
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Take the 8 ohm off and add a transformer to it that will allow the amp to run better. I always tried to keep the load at 2/3 or less of the amp rated power. 85 watts on a 100 watt amp should do fine for paging but if it runs music I would want more power. You can run 70 volt transformer on 25v output just figure a factor of 8 for the power difference. (70v tapped at 2 watt will give you 1/4 watt on 25v amp.)


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Re: 25volt vs 70volt
teldata1 #633425 10/23/19 12:20 AM
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Originally Posted by teldata1
Ok

So I just did a site survey on the external paging system in one of the 2 buildings which has a 35 watt bogen amplifier. The other building has a 100 watt speaker AMPLIFIER

We have 19 speakers tapped at 4 watts and several others that add up to 9 watts for a total of 85 watts. There is also a 8 ohm speaker on the system as well. They are using the 25 volt [OUTPUT] on the amplifier.

My question is how is this working? I thought that you shouldn't go over the wattage of the Amp?



Well, even after cleaning up your post to correct it and remove irrelevant information, I still don't completely understand you. Are you saying that the 35 watt amp has a total of 85 watts plus the 8 ohm speaker on it? Or is the 100 watt amp included in this somehow?

Assume here that it's only the 35 watt amp working into an 85 watt load and a speaker without a transformer that you are talking about and wondering why it works, of course it is going to work. Just don't expect to get much volume out of it (which is probably why it's cranked all the way up) and much life out of it either. If this were a larger amp driven with music and a more sophisticated protection design it probably would shut down. But with intermittent paging it looks like Bogen did a good job protecting this little amp from stupid.

So what I recommend you do is recommend to the customer that they replace that 35 W amp with another 100 W- maybe more depending on the additional speakers you might add.

Since all those existing speakers are tapped a 4 watts and have volume controls, after replacing the amp and getting everything operating correctly, you might want to check where they have those volume controls set to. If they are not turned all the way up, consider tapping down the speakers to maybe 1 or 2 watts to save on the size of the amp then just get rid of the volume controls. Remember, the wattage taps on the speaker transformers are there to adjust the volume. So if you have some that are too loud or not loud enough adjust the taps. You shouldn't need a volume control. That just wastes power.

And either get rid of that 8 ohm speaker or replace it with one with a transformer (or add a transformer).

-Hal
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CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
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