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Author Topic: multi building 70volt wiring - is this normal?  (Read 2184 times)

Jeff Hague

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multi building 70volt wiring - is this normal?
« on: March 07, 2012, 10:12:51 am »

Hi all! Let me start by saying that I'm a live sound guy, not an install guy. But I have installed and worked on some distributed systems and I understand the operation of the speaker side of the amps anyway. The input side seems pretty straight forward too in most of what I've worked on but I am looking at a project right now that has me a bit baffled...
I have been asked to "fix" a paging system that spans 4 buildings. These are exhibit halls and 3 of them are just rectangle buildings with no partition walls and your basic 8" ceiling tile speakers - 8 in the smallest building, 24 in another and 36 in the largest building. Each of these buildings has a single zone 70volt amp with 1 mic input and 1 line input. The 4th building is the main one and has a lobby area with 12 ceiling speakers (3 zones of 4) and a very large expo area with 2 clusters of four 2 way (non 70volt) boxes hanging from the ceiling. That building has a 12 channel mixer and a 4 zone 70volt amp with several mic and line inputs plus a "regular" amp to feed the clusters. (Luckily at this point I have not been asked to do anything in the expo space.) Sometimes they need each of the paging systems to be independent and sometimes they need to feed audio from 1 building to 1, 2 or all of the other 3. To facilitate that each building has a double pole triple throw switch marked "send", "local" and "receive". In building 1 for instance they set that switch to "send" and then in building 2 they set that switch to "receive" - that sends whatever audio input therte is from building 1 to building 2. They can also go to building 3 and set its switch to "receive" and then the audio feed from building 1 would go to buildings 2 and 3, etc. It also works the other way - send audio from building 3 back to 2 and 1, whatever. In the "local" position that building doesn't send or receive from any other building. It doesn't seem to be the most elegant or versatile way of doing things in my mind but it has done what they needed it to do.
These buildings were built at different times between 20 and maybe 10 years ago and no real maintenance has been done on any of these systems since the installs. There has unfortunately been a lot of "fix it quick" work done though by various people at different times.
The complaints are that the system hums and buzzes, some areas are too loud, some aren't loud enough, there is distortion, yadda, yadda, yadda. They do realize that the system is old, probably isn't setup to do what they really need it to do and that it needs some attention and possibly outright replacement.
So I went to take a look and its a real mess! 1 of the buildings has 4 mic jacks in various locations and each of those wires come back to the closet where the amp is and are simply twisted to each other, then spliced to a piece of wire that is about 6" long which is then spliced to a manufactured mic cable that has been cut to provide an XLR input to the amp - sweet! None of this is soldered either, just twisted and taped... Thats just 1 example, there is a lot of that kind of wiring. In their initial contact with me they wanted me to take a look at the speakers because they are old and they felt thats the place to start but my recommendation to them is to start with the wiring - get that cleaned up first and then take a look at the components - and they agreed.
Now, what baffles me is the way they have the various buildings wired together through these "Send, Local & Receive" switches... I expected that these would be line level but when I looked I found that they are amp level. The lines between the buildings that feed the switches come off of an amplifier output, through a transformer just like the ones on the ceiling speakers and then into the switches. Is that normal? Is that done to help make the long runs between buildings - probably 75' or so for each run. Is that done to reduce RFI or EFI since they didn't (or couldn't?) use balanced & shielded runs? I haven't looked closely at what taps they used on the transformer in each building but in building 1 the input side is using the 16 ohm tap and the output side is using the 2.5 watt tap. If this is normal, is there a method to determine how to wire that transformer for this and would it be different from building to building? If it is different, how would you go about determining it?
Initially I am planning on just cleaning up the obvious wiring issues but keeping it wired as it is now. I will follow that up with recommendations on replacement but any help explaining what they have going on here would be much appreciated - thanks!

Jeff
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Hal Bissinger/COMSYSTEC

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Re: multi building 70volt wiring - is this normal?
« Reply #1 on: March 07, 2012, 01:26:51 pm »

Quote
Now, what baffles me is the way they have the various buildings wired together through these "Send, Local & Receive" switches... I expected that these would be line level but when I looked I found that they are amp level. The lines between the buildings that feed the switches come off of an amplifier output, through a transformer just like the ones on the ceiling speakers and then into the switches. Is that normal? Is that done to help make the long runs between buildings - probably 75' or so for each run. Is that done to reduce RFI or EFI since they didn't (or couldn't?) use balanced & shielded runs? I haven't looked closely at what taps they used on the transformer in each building but in building 1 the input side is using the 16 ohm tap and the output side is using the 2.5 watt tap. If this is normal, is there a method to determine how to wire that transformer for this and would it be different from building to building? If it is different, how would you go about determining it?
Now, what baffles me is the way they have the various buildings wired together through these "Send, Local & Receive" switches... I expected that these would be line level but when I looked I found that they are amp level. The lines between the buildings that feed the switches come off of an amplifier output, through a transformer just like the ones on the ceiling speakers and then into the switches. Is that normal? Is that done to help make the long runs between buildings - probably 75' or so for each run. Is that done to reduce RFI or EFI since they didn't (or couldn't?) use balanced & shielded runs? I haven't looked closely at what taps they used on the transformer in each building but in building 1 the input side is using the 16 ohm tap and the output side is using the 2.5 watt tap. If this is normal, is there a method to determine how to wire that transformer for this and would it be different from building to building? If it is different, how would you go about determining it?

I'm not sure either. I do know that there are transformers specifically made to tap off a main 70.7v line to feed line level inputs on amps for other areas. Using a speaker transformer 16 ohm tap on a 70v line is going to load it down (if that's how you say it's wired). I also don't understand the room combining switches. Combining rooms with the main I can see but combining in groups I can't.
 
Do these people want to spend any money? There are lots of ways to do room combining now.
 
-Hal
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Jeff Hague

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Re: multi building 70volt wiring - is this normal?
« Reply #2 on: March 07, 2012, 02:03:06 pm »


 
Do these people want to spend any money? There are lots of ways to do room combining now.
 
-Hal

They do and they don't... The master plan for the facility calls for most if not all of these buildings to be torn down and replaced possibly within 2 years but apparently that has been the plan for at least the last few years and it has not yet happened. The Events Director needs the system working and is willing to at least fix whats there. She also wants to see what additional options there are but wants to be sure that any new components purchased can be reused in the new space (if that comes to be) or possibly used in some of the other buildings at the complex. She also does understand that wiring would not be one of those reusable components. I plan on presenting several different options and expect the decision to be based entirely on currently available budget.
Thanks!
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ProSoundWeb Community

Re: multi building 70volt wiring - is this normal?
« Reply #2 on: March 07, 2012, 02:03:06 pm »


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