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I'm looking for new headsets for an old Clear-com intercom system in a community theatre. All the plugs in the walls for the system are 3-pin XLR, but shopping around I can't find anything but 4 and 5 pin XLR connectors on headsets. So my question is, what's the difference between the three different plugs in an intercom system? If I were to invest in 4 or 5 pin headsets, would I be able to adapt them to work with the 3 pin plugs using plain 3-5 pin adapters? Does the 5 pin plug actually have 5 conductors or does it only have 4?

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3-pin is usually for balanced mono lines - a single balanced mic, etc.

4-pin can carry a mono signal to a headset & a mono unbalanced mic return.

5-pin can carry stereo to a headset & a mono unbalanced mic return.

6-pin can carry stereo to a headset & a mono balanced mic return.

If you try to reduce a 5 or 6 pin setup to run over 3-pin, basically all you could do is carry a stereo signal to the headset, with no return - or you could attempt to use one pin as ground for both mono signal & mic return, but I'm not sure how happy it would be doing that. I wouldn't risk it.

Ref: Wikipedia - XLR connector

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XLR-3 connectors for a Clear-Com intercom system might be for analog partyline systems. And actually, analog partyline systems are (or used to be) quite common in theatres.

If this is the case, it means you cannot directly plug a headset on these plugs, you need wired beltpacks on which you can plug a 4 or 5 pins headset.

The OP mentions that the main unit is a Clear-Com PS-451 which is actually a power supply and a main unit for such two-wires systems.

If you want to use this intercom system, you have to check wether currently available beltpacks would work with this main unit, and then ask for a quotation from a Clear-Com distributor (that might be the painful moment as these are usually not cheap). Or try to find some used ones.

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  • Ya, the main unit is only a few few from my desk.
    – ShemSeger
    Jun 22, 2018 at 14:35
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    Clear-Com PS-451
    – ShemSeger
    Jun 24, 2018 at 5:10
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    Nope, nothing. All the old sets were broke and thrown away before I got there.
    – ShemSeger
    Jun 24, 2018 at 14:57
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    This is the right answer. The headset connects to a belt pack, the belt pack connects to the 3 pin XLR line. Each belt pack has a male and a female XLR so that they can be chained. You aren't limited by the number of permanently installed jacks but by the capacity of the supply which is probably 100 headsets (but check the manual). For a beltpack the RS-451 was hugely popular back in the day and findable used on eBay etc. But older packs (the old all-stainless steel ones were amazingly tough.. I still have some) will work too. If for an analog clearcom system they will work.
    – little_birdie
    Jun 25, 2018 at 3:54
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    I should add that even though these systems are now old they are pretty much the gold standard of theatrical intercoms. Sure there are more advanced systems.. but so far as clear, effective voice communications goes they are excellent.
    – little_birdie
    Jun 25, 2018 at 4:01

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