TecPro 2 way selector switch

[danburns]

I've done a quick search, but can't find anything appropriate (all my results seem to refer to the use of a Tecpro system with 2 way radios!)

 

At a local amateur theatre I help out at, we've got a loudspeaker station and two hard wired cans points in the control box (like beltpacks but attatched to the wall) and we'd like to be able to use them on either circuit.

 

We've got circuit A set up as a show relay channel for the cast, and make calls over this circuit, and B is set up as crew talkback.

Both circuits come into and loop out of the box, and currently terminate in a terminal strip before being distributed to each point. We've got a set of DPDT switches that we want to put in before each headset point to be able to switch between the two - does anyone know if it's possible to common the +24V supply that feeds each circuit without any ill effects?

 

This is one of those jobs that we'd like to do with bits from the raven store if at all possible!

 

Cheers

 

Dan

[boatman]

The Tecpro PS711 three circuit power supply does almost the same. In that box, the audio circuits can be commoned by switches but the power and ground are commoned permanently. You could get away with a SPDT switch just switching the audio line from each wall box between the two circuits.

[adamharman]

As you've already got DPDT switches, then you don't need to common the power supply anyway, just common the ground and switch the audio and +v lines.

If using seperate power supplies and only switching the audio, then I'd common the +v via a couple of diodes at each pack to avoid any possible problems.

[dbuckley]

There are versions of the wall stations that can connect to multiple party lines, and they use exactly the same technology you will use - a switch.

 

Dont common the power; some power supplies dont like it...

[paulears]

If I understand it, you want the ability to switch a pack between two different comm lines?

 

Common the power supply DC voltage line BUT remember the PSU also provided the line load for the audio - if you have two comms lines, one connected to the PSU audio line and the other floating - the floating one will howl like crazy as the impedance changes and the gain goes wild! Tecpro is quite sensitive to the line impedance - with the packs working in high impedance bridging mode across a relatively low line impedance. All you need to do in the switching box is ensure that when you disconnect one line, and all the packs on it, that you add a resistor to maintain the impedance. Then, they can all carry on as usual. This is the case if your switch is at the PSU end. If your cable arrangement is that you have two separate lines 'going past', then switching the audio from a single pack to one or the other of them works fine.

 

The Tecpro PSU has three outputs and the little switches between them let them operate independently or linked.

[danburns]

Cheers all - I'll be giving it a go in the next couple of days so will let you know how it goes!

[boatman]

If it helps, the termination on the signal line in a Tecpro compatible system looks like this. I can't seen to get the code tags to work properly so you'll have to copy and paste it into Notepad and view it in a fixed pitch font.

 

There must be one (and only one) AC termination present on the line at all times for the system to be stable. If you are using a standard Tecpro PS711 unit it has them built in.

 

	   ----o---- SIGNAL LINE
	   |
	  .-.
	  | | 200R
	  | |
	  '-'
	   |
	   o--------+
	   |		|
	  .-.	   |+
	  | | 4k7  === 10uF
	  | |	  --- 35V
	  '-'	   |
	   |		|
	---o--------o--- GND

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