Clearcom/Telex Systems Integration

[MaxS]

I'm prepping for a show later this month, and we're renting out a Telex BTR-200 system to expand our current Clearcom wired IC. I was told that it wasn't compatible, so I sent the following email to our TD as a potential fix:

Given the model of the Telex basestation, it may be possible to wire an interface between the systems. The pinout for Clearcom 3XLR is as follows:
1 = Ground/Shield/Common
2 = +24-30 VDC
3 = Tx Signal (+5-10VDC for call)

The original, legacy Telex series pinout is as follows:
1 = Ground/Shield/Common
2 = - Signal Polarity
3 = + Signal Polarity

This essentially results in a balanced/unbalanced situation (Telex/Clearcom), with a few other considerations. IF the Telex basestation uses this pinout, and not the newer two-channel standard, it would be fairly straightforward to link the sources. This could be done either with a direct box or a custom device. The "other considerations" are as follows. All relate to the clear-com side: Pin 2 would have to be manually lifted, bypassing the DC supply. A 1uF, 50V, non-polar, capacitor would also be used on pin 3 to keep any DC "call-button" current from reaching the DI and the Telex basestation. Finally, the 3XLR pin 1 ground would be wired to "sleeve" on a TS connector, and pin 3 to "tip." This would provide an acceptable unbalanced-end signal for the DI, outputting a balanced XLR line, which is directly compatible with Telex.

This could all be done easily with a modified XLR on the clearcom side and a DI. Please confirm this if it is indeed the case and that the above set-up would function properly. It would definitely allow the Telex system to "hear" the clear-com system, however I can't speak in confidence for performance in the other direction. Using a DI in reverse/full-duplex isn't exactly kosher, and I'm not sure that it would work well, if at all. It may be worth looking in to if it's the only option, however.

After doing some more digging, however, I found that the manual describes how to use internal DIP switches to configure the unit for Clearcom interoperability on pages 20-21. This makes my previous plan irrelevant for this particular application.
http://www.swaindigital.com/ebay/BTR-200 TR-200 Operating Instructions.pdf

 

[museav]

Max, was this something where others might potentially run into the same problem and benefit by knowing how you solved it?

 

[MaxS]

Sure, it might. Sorry, it was late and I had just finished up striking a show. I had a "duh" moment when I finally found the manual for the unit, however the original solution that I had come up with may still be used by someone if it works. Telex also makes an interface unit of their own, the CCB-1.

 

[WooferHound]

MaxS said . . . - Quote -
Given the model of the Telex basestation, it may be possible to wire an interface between the systems. The pinout for Clearcom 3XLR is as follows:
1 = Ground/Shield/Common
2 = +24-30 VDC
3 = Tx Signal (+5-10VDC for call)

The original, legacy Telex series pinout is as follows:
1 = Ground/Shield/Common
2 = - Signal Polarity
3 = + Signal Polarity
- End quote -

The Clearcom pinout is accurate, but your Telex pinout does not include the power arrangement that powers the beltpack. It works very much like Phantom power where the Positive voltage appears on both of the 2 signal wires, and the Negative voltage appears on the shield/drain. Because of this it is not possible to make an adapter to connect the 2 different systems together.

 

[Chris15]

The Clearcom pinout is accurate, but your Telex pinout does not include the power arrangement that powers the beltpack. It works very much like Phantom power where the Positive voltage appears on both of the 2 signal wires, and the Negative voltage appears on the shield/drain. Because of this it is not possible to make an adapter to connect the 2 different systems together.

Um... When was the last time a transformer cared about a common mode voltage, say like phantom power?

 

[WooferHound]

A transformer will not pass a DC voltage, and it doesen't care if one side of a DC voltage is presented to both sides of any of the windings, therefore a transformer will not pass the voltage that an intercom system needs to operate, Therefore it is not possable to make an adapter to go between a Telix and a Clearcom system.

 

[MaxS]

A transformer will not pass a DC voltage, and it doesen't care if one side of a DC voltage is presented to both sides of any of the windings, therefore a transformer will not pass the voltage that an intercom system needs to operate, Therefore it is not possable to make an adapter to go between a Telix and a Clearcom system.

You forget that the Telex leg contains its own basestation, a self-powered wireless transceiver. Therefore it is already supplying its own power to its side of the transformer. The transformer won't pass along the phantom-style DC current from the signal wires in the Telex leg, which is actually ideal. The DC supply from either side has no means of reaching the other, allowing for a simpler design that only deals with the actual audio signals. The only limitation of what I've laid out is that calling will be disabled from both sides, between the capacitor/transformer on the Clearcom side, and the fact that a 20KHz tone is used on the Telex signal wire, as opposed to a voltage bump.

 

[Chris15]

You forget that the Telex leg contains its own basestation, a self-powered wireless transceiver. Therefore it is already supplying its own power to its side of the transformer. The transformer won't pass along the phantom-style DC current from the signal wires in the Telex leg, which is actually ideal. The DC supply from either side has no means of reaching the other, allowing for a simpler design that only deals with the actual audio signals. The only limitation of what I've laid out is that calling will be disabled from both sides, between the capacitor/transformer on the Clearcom side, and the fact that a 20KHz tone is used on the Telex signal wire, as opposed to a voltage bump.

The wireless base doesn't probably have a PSU in it, but it doesn't need one either.
The call should still work on each side of the ring, but it just won't traverse the connection between the two. If you find that the clearcom side is not behaving quite as it used to, throw a capacitor in series with the transformer and that ought to sort the problem out...