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[Matt Tudor]

We recently replaced the power supply and 1 intercom station at our university with new Audiocom 2-channel units with the long term intent of eventually upgrading the entire system to a 2 channels. For now, we are using just one channel of the power supply and one channel of the new 2-channel intercom. As our old intercom stations fail and get replaced, or as money allows, we will upgrade wall stations with 2 channel units. Since the old single channel system is run on sing pair shielded wire, we are going to have to update that also, which is were my question comes from.
According to the manual a single channel system "should" be run on 2 pair shielded wire and a 2 channel system should be run on 3 pair shielded wire. See fig. 6 and 7 here:
http://www.telexaudiocom.com/binary/WM-1000-WM-2000%20User%2 0Instructions.pdf
However, since our existing single channel system is run on a single pair with the DC common being on the shield drain instead of a second pair, I'm wondering if I can do the same thing with a two channel system and some 2pair shielded wire that I already have, instead of having to buy 3 pair shielded wire. Any thoughts?
If it comes down to pulling in new 3 pair wire, does anyone have any recommendations. Some of the conduits are already rather full so having the smallest diameter wire is important. No plenum spaces and most of the run is in floors in  conduit or free wire in pipe tunnels.
Thanks

[Rob Timmerman]

Matt Tudor wrote on Mon, 04 January 2010 12:46

According to the manual a single channel system "should" be run on 2 pair shielded wire and a 2 channel system should be run on 3 pair shielded wire. See fig. 6 and 7 here:  http://www.telexaudiocom.com/binary/WM-1000-WM-2000%20User%2 0Instructions.pdf However, since our existing single channel system is run on a single pair with the DC common being on the shield drain instead of a second pair, I'm wondering if I can do the same thing with a two channel system and some 2pair shielded wire that I already have, instead of having to buy 3 pair shielded wire.

Have you contacted the manufacturer to find out their recommendations?

[Matt Tudor]

Rob Timmerman wrote on Mon, 04 January 2010 19:20

Matt Tudor wrote on Mon, 04 January 2010 12:46 According to the manual a single channel system "should" be run on 2 pair shielded wire and a 2 channel system should be run on 3 pair shielded wire. See fig. 6 and 7 here:   http://www.telexaudiocom.com/binary/WM-1000-WM-2000%20User%2 0Instructions.pdf However, since our existing single channel system is run on a single pair with the DC common being on the shield drain instead of a second pair, I'm wondering if I can do the same thing with a two channel system and some 2pair shielded wire that I already have, instead of having to buy 3 pair shielded wire. Have you contacted the manufacturer to find out their recommendations?

Thanks, Rob for the time.
Their contact told me that there was no way a single channel system would run on single pair cable and that a 2 channel system would only run on a three pair cable. I know that a single channel will run on single pair, it's working (and has been for a long time) in three venues on campus and works every time someone use a mic cord to hook up a belt pack. So I know that at least part of what their guy told me is wrong, which calls into question the rest of what he told me. I'm hoping someone here might be able to provide some advice based on actual experience in the field.


I'm by no means an intercom expert and I'm curious why the need to put DC common on a separate, shielded pair of wires. DC shouldn't crosstalk into the audio circuits, should it? Why is this any different than phantom powering a mic? Is there a potential for the DC ground on the shield to be safety issue? Or is the current capacity of the shield/drain wire the issue?
Thanks again
Matt

[Don Boone]

Last 2 channel Clearcom I worked with (long ago) used just one STP cable. Shield was ground, one conductor was CH1 voice and the other conductor was +24VDC and CH2 voice.

Don

[Mac Kerr]

Don Boone wrote on Tue, 05 January 2010 13:53

Last 2 channel Clearcom I worked with (long ago) used just one STP cable. Shield was ground, one conductor was CH1 voice and the other conductor was +24VDC and CH2 voice. Don

That would have to have been a CC TW system which requires a TW10 series adapter to take to standard CC channels and combine them onto a single cable.

The OP's question is not about CC. it is about Telex Audiocom, a system that is not CC compatible.

To the OP, I would investigat the long term viability of Audiocom. I thought I had heard rumors it was being phased out. They already have an excellent and widely used system in RTS (also not compatible with Audiocom).

Mac

[Matt Tudor]

Mac Kerr wrote on Tue, 05 January 2010 13:00

Don Boone wrote on Tue, 05 January 2010 13:53 Last 2 channel Clearcom I worked with (long ago) used just one STP cable. Shield was ground, one conductor was CH1 voice and the other conductor was +24VDC and CH2 voice. Don That would have to have been a CC TW system which requires a TW10 series adapter to take to standard CC channels and combine them onto a single cable. The OP's question is not about CC. it is about Telex Audiocom, a system that is not CC compatible. To the OP, I would investigat the long term viability of Audiocom. I thought I had heard rumors it was being phased out. They already have an excellent and widely used system in RTS (also not compatible with Audiocom). Mac

Thanks for the tip Mac. I'll look into it, but the current system is all various vintages of Telex Audiocom so updates will probably have to be Audiocom compatible. The newest wall station has a dip switch that can change to set the station to a balanced mode compatible with Clear Com, maybe I'm not totally screwed.

[Mac Kerr]

Matt Tudor wrote on Tue, 05 January 2010 14:42

The newest wall station has a dip switch that can change to set the station to a balanced mode compatible with Clear Com, maybe I'm not totally screwed.

Clear Com and RTS are both unbalanced, Audiocom is balanced.

Mac

[Rob Timmerman]

The Telex Audiocom beltpacks will run a single channel down a single shielded pair just fine (I've even heard it work, sort of, on phantom-powered mic lines).  In your case, I suspect that the wall stations draw somewhat more power than a beltpack, due to the larger amplifier for the speaker.  Hence the use of a separate pair for the DC power return.  Depending on the grounding and shielding design of the system, and the cable and run lengths in question, you may be OK using the shield as the DC return.  Or it may not work.  

If a bit of crosstalk between channels is acceptable, I might consider using shielded CAT-5 or CAT-6 wiring.  That also gives you a potential upgrade path in the future.  This is, of course, assuming that you can't simply reuse your current wiring for the third pair that you need.

[Don Boone]

Quote:

The OP's question is not about CC. it is about Telex Audiocom, a system that is not CC compatible.

I snoozed right through the Audiocom part. I'm less familiar with Telex which may not be a problem in the future. I spec'd 4 of their ticket booth intercoms and when the customer pulled the trigger Telex said they were no longer available and there wouldn't be a replacement. Funny things happen when a company gets sold a few times.

Don