Tying two com systems together?

[Lambda]

At my school theater, we have two intercom systems. One of them is an Telex Audiocom PS2000L system, and the other is a portable system with no brand name, which I'm pretty sure is made by Eartec. The Eartec is the one that we use, the Telex is a legacy system that we no longer use most of the time. The Telex uses regular XLR3 mic cable, and the Eartec uses XLR4

Eartec system

Supposedly, they "upgraded" because of the wireless capability of the Eartec system and because it allowed us to have four stations in the booth instead of three. The wireless base unit is now broken, and we don't have the budget to fix it. That leaves us without wireless capability. We also have a bad shortage of XLR4 cable, which makes it a challenge to hook up all four headsets in the booth, especially when we have two spot-ops.
We also don't have enough com stations backstage. One stage right and another stage left, that's it. We need one in the orchestra area, and we'd like another in the green room.
Splitting the feed from the Eartec unit is difficult: It requires a special piece of hardware that contains a lot of circuitry. It doesn't seem to be digital, though, the circuitry is comprised mostly of op-amps and passive components, no microcontrollers.
The base unit is set up so that the four coms plug into the bottom row of connectors, the one labeled "master" goes to the now-defunct wireless unit, and the other connector next to the master connects to the splitter box backstage.
During musicals, we have to use the Telex system because it has a jack right in the orchestra area. Of course, we also have to use the Eartec system because we need four coms in the booth. It ends up that the SM wears two headsets at the same time, one Eartec and one Telex.

I want to figure out how to combine these two systems so that audio from either one can reach the other one. That way, I can put coms in the green room, orchestra area, and have more in the booth and backstage.
From what I can tell from the manual and from testing, the Telex system uses balanced audio in the same fashion as mics do, with 24 volts applied equally to pins 2 and 3.
The Eartec system is different: It uses XLR4, and from what I can tell it uses 12 and 6 volt power, applied on pins 1 and 3, and 2 and 4 respectively. I highly doubt it is balanced, because of the buzz on the line from the dimmers. (you can always tell when a light cue changes from the sound of the buzz)
In this system, I'm not quite sure how the audio is actually carried. Due to its size, weight, and the fact that it's practically built into my workbench, it wouldn't be all that easy to take my oscilloscope into school to really analyze this system.

So, any suggestions as to how I can do this on a spare-parts budget? I've considered just using two beltpacks, one from each system, taking the sound output, bringing it down to mic level and feeding it into the other mic input. But I don't want to lose two beltpacks. I'm sure there's a way to connect them simply, all I need to do is figure out how to send/receive audio from the Eartec system.

 

[David Ashton]

OK your Telex is not balanced, pin 1 is common 2 is 30 volt power and 3 is audio, the 4 pin is simply headset power, I guess you can plug your Telex subs in to your "master" on the eartec and this will work, but do not join the power supply from the telex in, you only need 1 power source, 2 could stuff it up.In effect your eartec box is a power supply and 4 subs in a box, all the common talkbacks use compatable wiring systems, I assume eartec do.If you really need to join them together with both power supplies then remove link 2 in the joining lead.

 

[museav]

OK your Telex is not balanced, pin 1 is common 2 is 30 volt power and 3 is audio, the 4 pin is simply headset power, I guess you can plug your Telex subs in to your "master" on the eartec and this will work, but do not join the power supply from the telex in, you only need 1 power source, 2 could stuff it up.In effect your eartec box is a power supply and 4 subs in a box, all the common talkbacks use compatable wiring systems, I assume eartec do.If you really need to join them together with both power supplies then remove link 2 in the joining lead.

Maybe you are thinking of the standard Clear-Com wiring, however the Telex PS2000L supplies +24VDC rather than +30VDC and can be set for either balanced AudioCom (Pin 1=Common, Pins 2 and 3=Audio and +24VDC) or unbalanced Clear-Com (Pin 1=Common, Pin 2=+24VDC and Pin 3=Audio) operation via an internal selector switch. It sounds like this system is operating in the balanced Telex AudioCom mode.

As to the Eartec, the master stations look like they're made in someone's basement and they seem to provide absolutely no technical information, so who knows.

Based on the above, the fact that your wireless has died and that the Telex PS2000L can function as either a one or two channel system, I would tend to look at switching over to the Telex system. Maybe you could get rid of the Eartec interface and make up some 3 pin to 4 pin cables that allow you to use the installed Eartec system cabling for Telex AudioCom communications.

 

[Lambda]

It sounds like this system is operating in the balanced Telex AudioCom mode.

That's correct, it is.

As to the Eartec, the master stations look like they're made in someone's basement and they seem to provide absolutely no technical information, so who knows.

My first thoughts exactly. The wiring inside seems to confirm this, the circuit board is glued to the side of the box (a commercially available product from Underwater Kinetics), and all the ground wires are attached to the negative terminal on the battery. Yikes. But the circuit board is professionally done, printed, with surface-mount components and a revision number labeled on it. The beltpack boxes are constructed similarly.
Here is a link to pictures of its internals.
This leads me to believe that it was made by Eartec. The one shown here is similar. Ours may have been part of a limited production run.

Based on the above, the fact that your wireless has died and that the Telex PS2000L can function as either a one or two channel system, I would tend to look at switching over to the Telex system. Maybe you could get rid of the Eartec interface and make up some 3 pin to 4 pin cables that allow you to use the installed Eartec system cabling for Telex AudioCom communications.

I've considered it, but we don't have enough beltpacks and headsets to do that. We need at least 4 in the booth, one in each wing backstage, one near the orchestra, and I'd like to have one in the greenroom (but we can live without). That's 7, I don't have the inventory sheet in front of me but I think we only have 4 or 5 working Telex beltpacks.

 

[museav]

My first thoughts exactly. The wiring inside seems to confirm this, the circuit board is glued to the side of the box (a commercially available product from Underwater Kinetics), and all the ground wires are attached to the negative terminal on the battery. Yikes. But the circuit board is professionally done, printed, with surface-mount components and a revision number labeled on it. The beltpack boxes are constructed similarly.
Here is a link to pictures of its internals.
This leads me to believe that it was made by Eartec. The one shown here is similar. Ours may have been part of a limited production run.

I agree that it looks like an Eartec product, their wired intercom products do look a bit like somebody's weekend DIY project. The real issue is that the Eartec web site provides literally no detailed product or technical information on their wired intercom products.

This is further complicated by the fact that your systems does seem to be a custom or no longer offered product. The standard TCX hybrid system includes the four headset connections and the connection for the wireless transceiver but does not include the connection to the installed wired locations that your system apparently has or the related interface box you mentioned, which may be a power supply for any beltpacks on the installed system as the TCX itself is apparently limited to powering only the four local headsets.