# 70v PA system



## te12co2w

We have been asked to trouble shoot a PA system in a senior center. Quite a few of the speakers don't work or maybe they are working but at very low volume. Th amp is a Speco P-60FACD. This is a 60 watt 70v system. The speakers I have looked at are Soundolier FD. I have found one Dukane 5a607 in there. All the speakers that I have looked at have a 70.7v transformer, 8 ohms except one. One of the speakers has a 25v transformer. I have counted a total of 36 speakers on this system. There might be some that I am not aware of, but probably not too many. Most of the speakers that I have looked at are on the one watt tap. One speaker was on the .5w tap. One was on the 2 watt tap. I don't think they are overdriving their amp? He said it was replaced almost a year ago. Someone spilled a drink in the old one.
I found one speaker with a 25v transformer, and that one was working. I have only opened 10 or 12 of these speakers. They are fed with something that looks like beldon cable. Some of it has a ground some of it doesn't. Black and red wire. Bigger than phone wire but smaller than #14. 
I have tried to check voltage at the speaker locations, but am not getting any thing meaningful to me. Less than one volt and it seems to change a little during testing. Used 2 different fluke meters. One with a low z adapter, one without, and a milwaukee on lowz and regular. Is there any way to test for proper voltage at speaker locations?
One room has 6 speaker that don't appear to work at all. The maintenance man says they haven't worked since he has been there. 5 years. 2 of those speakers might have very reduced volume on them. Some of these speakers are in an addition to this building. Anything could have happened.
Down one hallway the 2 speakers at the very end work fine, but 3 or 4 between those speakers and presumably the amp either don't work at all or at very reduced volume. Some speakers have a volume knob right in the middle of the speaker grill. Should I take those out of the circuit entirely?
Anything could have happened over the years, but I am working under the impression that this all worked at some point.
Oh yeah, the zones leave the amp in lamp/speaker cord, but each speaker has this beldon type cable to it, so there is a splice somewhere. Very crowded up in the attic. Lots of equipment, fire walls, etc. It is going to be a bear to chase out. Thanks. Sorry for such a long post. Maybe someone will take the time to read through it.


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## wildleg

mismatched speaker impedance can play havoc with any audio system. that's all I know. I would disconnect anything not impedance matched and if it worked ok that's your problem. maybe someone will come along soon with a better suggestion.


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## Semi-Ret Electrician

Have you tried a new speaker w/ a 70.7 trans ?

Over the years they could all be bad.

I would not overthink this


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## wendon

Take one of the speakers out and connect it directly to the amp. If the speaker with the 25 volt xfmr is hooked to the 1 watt tap, I doubt if it would hurt anything. Are you sure that the speaker is only made for 25 volt? Most of those paging speakers have taps for both. Are there volume controls for different areas? Make sure that someone hasn't installed the wrong type. At 70 volts it wouldn't be uncommon for the speakers to be fed with smaller wire. I presume you checked to make sure the new amp is connected correctly? (Com and 70 volt tap)


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## drsparky

70 volt system, 60 watt amp: the 25W goes away, just toss it. Add the total wattage of the taps and it must be less than 60 w. Volume is set by the taps ie. you could have 120 very quiet 1/2 watt speakers or 1 loud 30 watt speakers and 30 quiet 1 watt speakers. Just keep the total speaker tap wattage below the amps total output. don't worry about impedance of the system.


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## guest

te12co2w said:


> We have been asked to trouble shoot a PA system in a senior center. Quite a few of the speakers don't work or maybe they are working but at very low volume. Th amp is a Speco P-60FACD. This is a 60 watt 70v system. The speakers I have looked at are Soundolier FD. I have found one Dukane 5a607 in there. All the speakers that I have looked at have a 70.7v transformer, 8 ohms except one. One of the speakers has a 25v transformer. I have counted a total of 36 speakers on this system. There might be some that I am not aware of, but probably not too many. Most of the speakers that I have looked at are on the one watt tap. One speaker was on the .5w tap. One was on the 2 watt tap. I don't think they are overdriving their amp? *He said it was replaced almost a year ago. Someone spilled a drink in the old one.*
> I found one speaker with a 25v transformer, and that one was working. I have only opened 10 or 12 of these speakers. They are fed with something that looks like beldon cable. Some of it has a ground some of it doesn't. Black and red wire. Bigger than phone wire but smaller than #14.
> I have tried to check voltage at the speaker locations, but am not getting any thing meaningful to me. Less than one volt and it seems to change a little during testing. Used 2 different fluke meters. One with a low z adapter, one without, and a milwaukee on lowz and regular. Is there any way to test for proper voltage at speaker locations?
> One room has 6 speaker that don't appear to work at all. The maintenance man says they haven't worked since he has been there. 5 years. 2 of those speakers might have very reduced volume on them. Some of these speakers are in an addition to this building. Anything could have happened.
> Down one hallway the 2 speakers at the very end work fine, but 3 or 4 between those speakers and presumably the amp either don't work at all or at very reduced volume. Some speakers have a volume knob right in the middle of the speaker grill. Should I take those out of the circuit entirely?
> Anything could have happened over the years, but I am working under the impression that this all worked at some point.
> Oh yeah, the zones leave the amp in lamp/speaker cord, but each speaker has this beldon type cable to it, so there is a splice somewhere. Very crowded up in the attic. Lots of equipment, fire walls, etc. It is going to be a bear to chase out. Thanks. Sorry for such a long post. Maybe someone will take the time to read through it.


Since someone spilled a drink in the old amplifier, I am willing to bet that the speakers that are at low volume or don't work are blown out and need to be replaced. A shorted amplifier will put out all kinds of very bad things to the output, including DC voltage that will either fry the 70 transformers or permanently magnetize them making them unable to pass audio any more. 

To start with, disconnect ALL of the speakers and see if any of the lines are shorted. Fix any that are. 

Next, to check for opens, short ONE speaker location at a time and look for continuity at the amp "home run" end. Any that show no continuity means a break in the wire. Repeat for all speaker locations and be sure to only have ONE speaker at a time shorted.

Finally, take each speaker, one at a time, to the amplifier and test it with a music source. Replace any that are not clean and reasonable volume for the tap in use. 

See this thread http://www.electriciantalk.com/f10/70v-distributed-line-pa-systems-facts-myths-tips-72371/ for more info. 

The speaker wire you referred to sounds like Belden 8451/9451 which is only 22ga. and is way too small for this application. MINIMUM wire size for most 70v systems should be 16ga.


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## te12co2w

*Thank you*

Thanks for all the replies. I will be back with info as I gather it. I like this site!


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## te12co2w

Semi-Ret Electrician said:


> Have you tried a new speaker w/ a 70.7 trans ?
> 
> Over the years they could all be bad.
> 
> I would not overthink this


 I have not tried a new speaker, but did try a known working one in place of a nonworking one. No deal.


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## te12co2w

wendon said:


> Take one of the speakers out and connect it directly to the amp. If the speaker with the 25 volt xfmr is hooked to the 1 watt tap, I doubt if it would hurt anything. Are you sure that the speaker is only made for 25 volt? Most of those paging speakers have taps for both. Are there volume controls for different areas? Make sure that someone hasn't installed the wrong type. At 70 volts it wouldn't be uncommon for the speakers to be fed with smaller wire. I presume you checked to make sure the new amp is connected correctly? (Com and 70 volt tap)


 I will connect one or two speakers directly to the amp. Don't know why I didn't think of it at the time. The nurses won't like me taking over their little cubbyhole, but they will get over it. The speaker transformer says 25v primary. There is one volume control that supposedly operates the speakers in the dining room. I wrote down the # but I don't have it right now. It is a soundelier if memory serve me well. Com & 70v correct.


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## te12co2w

drsparky said:


> 70 volt system, 60 watt amp: the 25W goes away, just toss it. Add the total wattage of the taps and it must be less than 60 w. Volume is set by the taps ie. you could have 120 very quiet 1/2 watt speakers or 1 loud 30 watt speakers and 30 quiet 1 watt speakers. Just keep the total speaker tap wattage below the amps total output. don't worry about impedance of the system.


 Total is definitely below 60w


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## te12co2w

mxslick said:


> Since someone spilled a drink in the old amplifier, I am willing to bet that the speakers that are at low volume or don't work are blown out and need to be replaced. A shorted amplifier will put out all kinds of very bad things to the output, including DC voltage that will either fry the 70 transformers or permanently magnetize them making them unable to pass audio any more.
> 
> To start with, disconnect ALL of the speakers and see if any of the lines are shorted. Fix any that are.
> 
> Next, to check for opens, short ONE speaker location at a time and look for continuity at the amp "home run" end. Any that show no continuity means a break in the wire. Repeat for all speaker locations and be sure to only have ONE speaker at a time shorted.
> 
> Finally, take each speaker, one at a time, to the amplifier and test it with a music source. Replace any that are not clean and reasonable volume for the tap in use.
> 
> See this thread http://www.electriciantalk.com/f10/70v-distributed-line-pa-systems-facts-myths-tips-72371/ for more info.
> 
> The speaker wire you referred to sounds like Belden 8451/9451 which is only 22ga. and is way too small for this application. MINIMUM wire size for most 70v systems should be 16ga.


 Lots of good ideas here. I will try them all. I did read your post for 70v pa systems before I went there the first time. Appreciate it.


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## Speedskater

For other readers, this white paper.

*Constant-Voltage Audio Distribution Systems*
http://www.rane.com/note136.html

Dennis Bohn, Rane Corporation
RaneNote 136 written 1997; last revised 3/07


25, 70.7 & 100 Volts
U.S. Standards
Just What_ is_ "Constant" Anyway?
Voltage Variations -- Make Up Your Mind
Calculating Losses -- Chasing Your Tail


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## DCooper

Are these in-wall or in ceiling speakers? If they are in ceiling and not a drop ceiling start pulling them down one by one. I found one that some genius installed where the wires had been pinched by the housing and the Ductwork, speaker was too deep.


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## Birken Vogt

The 25v tx wired across a 70v line will work; it just gives a higher wattage setting than indicated. Some tx have the taps dual marked for wattages at the different voltages.


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## te12co2w

DCooper said:


> Are these in-wall or in ceiling speakers? If they are in ceiling and not a drop ceiling start pulling them down one by one. I found one that some genius installed where the wires had been pinched by the housing and the Ductwork, speaker was too deep.


 In ceiling. Most of them do not have a back box. Loose cellulose fiber insulation about 2" deep up there. Taking each one out creates a big mess.


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## te12co2w

Finally found one of the main problems. One feed to the dining room had been disconnected altogether. Took 2 of us more than 2 days to find it. That got a big issue resolved. The 2 nurses that had been there the longest said that they had never heard those speakers working.
There are a mix of 25v and 70v speakers in this system. There are 4 zones. The home runs from the amp are all 2 conductor speaker wire. 2 of those runs change to some beldon wire or some other brand in the ceiling. The other 2 pass through fire walls and the speakers down those two hallways seem to be working. I decided not to chase them out. The other 2 zones each have a mix of the 25v and 70v speakers. The 25v speakers seem the loudest in those zones. I almost have to believe combining the 2 types is not the best idea. Since the 25v speakers seem the loudest, would it be reasonable to expect better performance if all the 70v speakers were replaced with 25v?
The loudest zone is one with almost all 25v speakers. There is no way to control the volume of each zone independently. Therefore, the people listening to that zone always complain that the music is too loud, and the people listening to the other three zones sometimes can barely hear it at all. Would an independent volume control located in each zone fox this? i.e. could I wire from zone 1 to the attic, then drop down in the wall to a volume control and then to the speakers? That seem logical to me. I don't have authorization to modify anything yet.
One more question? What code article (s) covers this? It seems 70 volts might create some wiring issues?


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## te12co2w

Speedskater said:


> For other readers, this white paper.
> 
> *Constant-Voltage Audio Distribution Systems*
> http://www.rane.com/note136.html
> 
> Dennis Bohn, Rane Corporation
> RaneNote 136 written 1997; last revised 3/07
> 
> 
> 25, 70.7 & 100 Volts
> U.S. Standards
> Just What_ is_ "Constant" Anyway?
> Voltage Variations -- Make Up Your Mind
> Calculating Losses -- Chasing Your Tail


 Thanks for posting this. I will copy and read with your permission.


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## guest

te12co2w said:


> Finally found one of the main problems. One feed to the dining room had been disconnected altogether. Took 2 of us more than 2 days to find it. That got a big issue resolved. The 2 nurses that had been there the longest said that they had never heard those speakers working.
> There are a mix of 25v and 70v speakers in this system. There are 4 zones. The home runs from the amp are all 2 conductor speaker wire. 2 of those runs change to some beldon wire or some other brand in the ceiling. The other 2 pass through fire walls and the speakers down those two hallways seem to be working. I decided not to chase them out. The other 2 zones each have a mix of the 25v and 70v speakers. The 25v speakers seem the loudest in those zones. *I almost have to believe combining the 2 types is not the best idea. *


No it is not the best idea, it is a very bad idea and technically a Code violation. 



te12co2w said:


> Since the 25v speakers seem the loudest, *would it be reasonable to expect better performance if all the 70v speakers were replaced with 25v?*


No and you will run the risk of overloading the amplifier or burning up the transformers in the speakers. 



te12co2w said:


> The *loudest zone is one with almost all 25v speakers.* There is no way to control the volume of each zone independently. Therefore, the people listening to that zone always complain that the music is too loud, and the people listening to the other three zones sometimes can barely hear it at all. *Would an independent volume control located in each zone fox this? i.e. could I wire from zone 1 to the attic, then drop down in the wall to a volume control and then to the speakers? *That seem logical to me. I don't have authorization to modify anything yet.


No surprise about the loudest zone being the 25v zone. And yes, they make volume controls for 70v systems and yes you can get one for each zone and do as you suggested. Each control will get a "home run" line from the amp (and a SINGLE run of at least 16ga 2 conductor can be used to feed all four zones, wire each volume control as if were wiring receptacles for example) and then from the volume control to all of the speakers in the selected zone. 



te12co2w said:


> One more question? What code article (s) covers this? It seems 70 volts might create some wiring issues?


That was actually 2 questions, and I don't have my code book handy but there is a section specifically addressing audio system wiring. (Google is your friend, I found it)..Art. 640 is the one you need to look at. :thumbup:


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## guest

Birken Vogt said:


> The 25v tx wired across a 70v line will work; it just *gives a higher wattage setting than indicated.* * Some tx have the taps dual marked for wattages at the different voltages.*


Correct and correct. BUT, a speaker where the taps are not SPECIFICALLY marked for BOTH voltages should not be used on the wrong voltage. You can overload the amplifier, blow out the speaker or burn up the transformer. (Think about it.. using a 25v speaker on a 70v system is, in theory, the same as running a 120v load on 336 volts, a 2.8 times overvoltage.)

Mixing speaker voltages in the system is bad practice and _technically an NEC violation._ (Equipment not used according to listing.)


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## te12co2w

There is a note in the installation manual That TV71? called to my attention. There is a jumper internal to this amp that can select for 25v or 70v. I did not open this thing up when I was fooling with it. Thanks for all the replies.


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