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Author Topic: Relay with 70V volume control  (Read 4954 times)

Matt Tudor

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Relay with 70V volume control
« on: December 19, 2012, 11:49:41 pm »

Was working on a 70V paging system today in the lobby and hall of our conference center and found relays wired with the local volume controls in the various zones. Having relays with the potentiometers is new to me and I'm hoping someone here can shed some light on this, and explain what I'm looking at.  The potentiometers are Soundolier AT-75, the relay has a model number MS 64-913, ( appears to be a generic part number used by several manufactures?) The Soundolier PN led me to Atlas site but I couldn't find this entire package listed anywhere.

For each Volume control I have 1 or more 16/2 cables wire in parallel with the coil of the relay, I also have 3 smaller cables (2 conductor of various gauges). Of theses three, the black wires are tied to the potentiometer common and relay common, one white wire is relay common, and the other two white wire are tied to NO pole on the relay, which is also wired to potentiometer in. Potentiometer out is tied to relay NC. Me looking at it, it looks like its using voltage on the speaker line to pull in the relay to switch between two sources. accept I only have one source and that doesn't explain how the potentiometer fits into the system.

I've found a few references on-line, mostly home audio and DIY forums, that talk about relay volume control compared to steppers, but no wiring diagrams. Of course none of the wires in this system are labeled in a way that means anything. FWIW the building is about 25 years old, and this much of the system is probably original to the building. Is this a different/better way of controlling volume? This ring a bell to anyone?
Thanks in advance
Matt
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Mac Kerr

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Re: Relay with 70V volume control
« Reply #1 on: December 19, 2012, 11:54:50 pm »

Was working on a 70V paging system today in the lobby and hall of our conference center and found relays wired with the local volume controls in the various zones. Having relays with the potentiometers is new to me and I'm hoping someone here can shed some light on this, and explain what I'm looking at.  The potentiometers are Soundolier AT-75, the relay has a model number MS 64-913, ( appears to be a generic part number used by several manufactures?) The Soundolier PN led me to Atlas site but I couldn't find this entire package listed anywhere.

For each Volume control I have 1 or more 16/2 cables wire in parallel with the coil of the relay, I also have 3 smaller cables (2 conductor of various gauges). Of theses three, the black wires are tied to the potentiometer common and relay common, one white wire is relay common, and the other two white wire are tied to NO pole on the relay, which is also wired to potentiometer in. Potentiometer out is tied to relay NC. Me looking at it, it looks like its using voltage on the speaker line to pull in the relay to switch between two sources. accept I only have one source and that doesn't explain how the potentiometer fits into the system.

I've found a few references on-line, mostly home audio and DIY forums, that talk about relay volume control compared to steppers, but no wiring diagrams. Of course none of the wires in this system are labeled in a way that means anything. FWIW the building is about 25 years old, and this much of the system is probably original to the building. Is this a different/better way of controlling volume? This ring a bell to anyone?
Thanks in advance
Matt

It's a priority relay. It is meant to bypass the volume control when pages are made. the idea being that if the talent turns down the program feed the announcements still get through. The relay is tripped by the PTT switch on the announce mic.

Mac
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Hal Bissinger/COMSYSTEC

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Re: Relay with 70V volume control
« Reply #2 on: December 20, 2012, 04:47:08 pm »

It's a priority relay. It is meant to bypass the volume control when pages are made. the idea being that if the talent turns down the program feed the announcements still get through. The relay is tripped by the PTT switch on the announce mic.

Mac

Hmmm, probably but it might be "home brew". Atlas doesn't make an AT-75(PA). Is the relay part of the volume control or just hanging there by the wiring?
 
Here's the spec sheet for the AT(PA) series. And these things are not a potentiometers. They are auto-transformers with a rotary switch off the taps.
 
http://www.atlassound.com/FileDownload/Data%20Sheet_____ID2105.pdf
 
The way it works is when you apply 24vdc to the +24 and -24 terminals on the Phoenix connector the relay pulls in bypassing the control and the volume goes to full. From your wiring explanation it sounds like that's what you have does.
 
-Hal
 
 
« Last Edit: December 20, 2012, 04:53:33 pm by Hal Bissinger/COMSYSTEC »
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Matt Tudor

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Re: Relay with 70V volume control
« Reply #3 on: December 20, 2012, 10:20:36 pm »


Hmmm, probably but it might be "home brew". Atlas doesn't make an AT-75(PA). Is the relay part of the volume control or just hanging there by the wiring?
 
Here's the spec sheet for the AT(PA) series. And these things are not a potentiometers. They are auto-transformers with a rotary switch off the taps.
 
http://www.atlassound.com/FileDownload/Data%20Sheet_____ID2105.pdf
 
The way it works is when you apply 24vdc to the +24 and -24 terminals on the Phoenix connector the relay pulls in bypassing the control and the volume goes to full. From your wiring explanation it sounds like that's what you have does.
 
-Hal

Ahhh, OK. Makes sense. I can test that tomorrow easily enough to verify. Thanks to both of you for the help. The linked page isn't the particular device that I have but What I've got looks to be commercially made, possibly a previous generation. That also explains the extra wire hooked up to the PTT switch on the mic and the need for the monster power supply in the equipment rack.

This whole project has been a bit of a zoo, even without the addition of priority override relays. As I go though this system, I'm finding 2 distinctly different types of labels, and enough wire nut splices tossed above ceiling tiles to make me believe the system has gone through at least two major modifications already, with no significant documentation.  If I could just find the ends of wires 61, 23, and 14...... ::)

It's a good day when I learn something
Thanks again
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Hal Bissinger/COMSYSTEC

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Re: Relay with 70V volume control
« Reply #4 on: December 21, 2012, 10:38:48 pm »

Yeah, if yours says AT75 it's probably from years ago because as you see they no longer make the AT75 with a relay. Does it have a Phoenix connector or wire leads?
 
Keep in mind that the picture in that brochure doesn't show the volume control with the relay.
 
I don't know why the power supply is so large. Are there a lot of these volume controls? The relay coils only draw 10ma @24vdc.
 
-Hal
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Matt Tudor

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Re: Relay with 70V volume control
« Reply #5 on: December 25, 2012, 06:43:19 pm »

Yeah, if yours says AT75 it's probably from years ago because as you see they no longer make the AT75 with a relay. Does it have a Phoenix connector or wire leads?
 
Keep in mind that the picture in that brochure doesn't show the volume control with the relay.
 
I don't know why the power supply is so large. Are there a lot of these volume controls? The relay coils only draw 10ma @24vdc.
 
-Hal

You guys were right, works just like you said. Thanks. WRT the size of the power supply it's, 10A @24VDC. So Far, I've only found 3 volume controls with the relays, and one uncontrolled zone, but one of those three was hidden behind a bookshelf and half forgotten about. I've also got more relay control wires connected together in one junction than I have volume controls so there could be more out there hidden in closets somewhere. At least one of these volume controls is 200+ feet out from the power supply so the original designer may have been anticipating some cable loss. Just gotta keep looking...
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Hal Bissinger/COMSYSTEC

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Re: Relay with 70V volume control
« Reply #6 on: December 25, 2012, 10:09:38 pm »

At least one of these volume controls is 200+ feet out from the power supply so the original designer may have been anticipating some cable loss.

Wire resistance and voltage drop wouldn't be a reason to use a higher current power supply. Larger wire would, but I kinda think without getting out my calculator that 10ma with 200 feet of 16ga isn't going to be a problem.
 
-Hal
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Re: Relay with 70V volume control
« Reply #6 on: December 25, 2012, 10:09:38 pm »


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