ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2  All   Go Down

Author Topic: DC Relay in a 70v System?  (Read 7917 times)

Scott Hofmann

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 344
DC Relay in a 70v System?
« on: August 29, 2019, 02:48:33 pm »

I want to incorporate a TOA  S-04S(T) chime module in an existing TOA 900 series mixer/amp in an auditorium’s 70v show relay/paging system. The chime will obviously go to all the areas of the theatre that have show relay speakers already. The catch is that the lobby does not have any existing 70v speakers and that’s what really needs the chime signal for start of show and intermission.
There is a show relay speaker in the lobby box office though, so the wiring is accessible and it would be relatively easy to add a couple of speakers in the lobby.

But here’s the issue…. I don’t want the show relay and paging constantly going thru the “new” lobby speakers, just the chime. So my idea would be to send a low-voltage DC signal on the speaker wires (system-wide) which would operate a relay to close the speaker connection to the new speakers only when someone pushed a DPST momentary chime button. The 70v transformers would block the DC from getting to all the speakers.

Is there a reason this wouldn’t work and would I need to use capacitors to keep from feeding the DC back into the mixer/amplifier’s output terminals?
Logged
Scott Hofmann

Scott Holtzman

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 6003
  • Ghost AV - Avon Lake, OH
    • Ghost Audio Visual Systems, LLC
Re: DC Relay in a 70v System?
« Reply #1 on: August 29, 2019, 02:55:10 pm »

I want to incorporate a TOA  S-04S(T) chime module in an existing TOA 900 series mixer/amp in an auditorium’s 70v show relay/paging system. The chime will obviously go to all the areas of the theatre that have show relay speakers already. The catch is that the lobby does not have any existing 70v speakers and that’s what really needs the chime signal for start of show and intermission.
There is a show relay speaker in the lobby box office though, so the wiring is accessible and it would be relatively easy to add a couple of speakers in the lobby.

But here’s the issue…. I don’t want the show relay and paging constantly going thru the “new” lobby speakers, just the chime. So my idea would be to send a low-voltage DC signal on the speaker wires (system-wide) which would operate a relay to close the speaker connection to the new speakers only when someone pushed a DPST momentary chime button. The 70v transformers would block the DC from getting to all the speakers.

Is there a reason this wouldn’t work and would I need to use capacitors to keep from feeding the DC back into the mixer/amplifier’s output terminals?

I would put the DC blocking cap on the amp for safety.  Other than that you have described how a phone works, DC signalling AC audio....Should work fine
Logged
Scott AKA "Skyking" Holtzman

Ghost Audio Visual Solutions, LLC
Cleveland OH
www.ghostav.rocks

Kurt J Nemer

  • Newbie
  • *
  • Offline Offline
  • Posts: 7
Re: DC Relay in a 70v System?
« Reply #2 on: August 29, 2019, 03:10:58 pm »

Probably will get an audible pop when you apply the DC, might not be problem though.
 I"d be concern about the DCR of all those 70V transformers in parallel, might look a lot like a short circuit to DC.

If both speaker leads are ungrounded maybe set it up like phantom power. Apply the DC from a transformer "center tap" to ground.
Logged

Marc Sibilia

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 71
  • Princeton, New Jersey
Re: DC Relay in a 70v System?
« Reply #3 on: August 29, 2019, 03:12:53 pm »

Is there a reason this wouldn’t work and would I need to use capacitors to keep from feeding the DC back into the mixer/amplifier’s output terminals?

You can't apply DC directly to the transformer.  While it is true that the DC won't pass, it can cause saturation in the primary of the transformer, which will at a minimum cause distortion, and if the saturation of the iron is complete, will cause the amplifier will see a near dead short (the very low DC resistance of the primary instead of the transformed by the turns ratio squared impedance of the load connected to the secondary).  You will need a large enough capacitor to pass the audio into the transformer and block the DC.
Logged

David Allred

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1842
Re: DC Relay in a 70v System?
« Reply #4 on: August 29, 2019, 03:32:56 pm »

My solution 1) Play a chime track through the system.
My solution 2) Buy a wireless doorbell (chime).
Logged

Hal Bissinger/COMSYSTEC

  • Full Member
  • ***
  • Offline Offline
  • Posts: 215
    • COMSYSTEC
Re: DC Relay in a 70v System?
« Reply #5 on: August 30, 2019, 02:26:48 am »

How hard would it be to run the wiring for the new speakers back to the amp location and provide a relay there?
-Hal
Logged

Scott Hofmann

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 344
Re: DC Relay in a 70v System?
« Reply #6 on: August 30, 2019, 10:17:42 am »

How hard would it be to run the wiring for the new speakers back to the amp location and provide a relay there?
-Hal
After reviewing all the great posts, I think the best solution would be to add a small amp with the chime module at the amp rack location and run a speaker line from it to two new lobby speakers, which will not put show relay/paging into the new speakers. Also take the line out of this amp and feed into an input on the existing mixer/amp to get the chime signal to all the existing 70v show relay/paging speakers.
Thanks for the great discussion!
Logged
Scott Hofmann

Scott Hofmann

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 344
Re: DC Relay in a 70v System?
« Reply #7 on: August 30, 2019, 10:22:31 am »

My solution 1) Play a chime track through the system.
My solution 2) Buy a wireless doorbell (chime).
I appreciate your suggestions but....
Solution 1: show relay/paging will still go to the lobby which is not desired.
Solution 2:they have just put about a dozen of these all over the place (without my input) and you can barely hear them, especially in the lobby! Hence the need for a new plan.
Logged
Scott Hofmann

David Allred

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1842
Re: DC Relay in a 70v System?
« Reply #8 on: August 30, 2019, 01:05:08 pm »

I appreciate your suggestions but....
Solution 1: show relay/paging will still go to the lobby which is not desired.
Solution 2:they have just put about a dozen of these all over the place (without my input) and you can barely hear them, especially in the lobby! Hence the need for a new plan.

Maybe you could put a relay to turn on and off those speakers.   ;D

The doorbell would work in my local community theatre lobby.  You must be on a larger scale. 
Logged

Scott Hofmann

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 344
Re: DC Relay in a 70v System?
« Reply #9 on: August 30, 2019, 03:26:24 pm »

Maybe you could put a relay to turn on and off those speakers.   ;D

The doorbell would work in my local community theatre lobby.  You must be on a larger scale.
1500 seat auditorium.
Logged
Scott Hofmann

ProSoundWeb Community

Re: DC Relay in a 70v System?
« Reply #9 on: August 30, 2019, 03:26:24 pm »


Pages: [1] 2  All   Go Up
 



Page created in 0.037 seconds with 25 queries.