Add a Phone/Computer into Clearcom

[joeyfergie]

During the last show I was working on, just before we began our second last show (which was also adjudication night!), our clearcom to the orchestra went out. Later figured out it was a bad cable, but due to time/lack of extra cables, there was no way to immediately fix it at the time. What we did instead was take one of the house phones, as well as my cell phone, and made an open line between them, giving one phone to the SM in the booth, and the other to the Musical Director in the pit. Worked well enough for the 2 final performances. However, I would like to create something so that if something like this happened again, or if we needed more beltpacks than we had, there was a solution.

This is what i was thinking. An adapter which goes from 4pin XLR (clearcom headset connector) to either a 1/8" TRS or dual 1/8" TS, so that you can hook it into a phone or a computer. This way, you would either be able to call the phone, or use Skype on the computer and "join" the clearcom conversation. Has anyone tried anything like this before, and would it work? You would need a beltpack or basestation to connect this to (our basestation has a headset input), and I am hoping that it would be able to just add the new device in. Any help or suggestions would be greatly appreciated!!

 

[waynehoskins]

Interesting idea.

The Clear-com bus is line-level unbalanced audio (I think it's about -10, while RTS is closer to +4). For a computer connection, what you would probably want is called a duplex hybrid circuit, to convert the two-wire bidirectional audio on the bus to four-wire unidirectional audio (separate transmit and receive lines). They're simple enough to build, and I believe they're commercially made as well. I don't think you should need any level conversion since it's reasonably matched to line-level in and out of a soundcard.

Telephone interconnection would be trickier. The POTS bus is bidirectional, but it also has power superimposed on it, and I don't know what level and impedance transformations would be necessary. I think I've seen commercial interfaces for exactly that. If it's a business telephone system (key or others), then who knows. Anything is possible, but not all things are practical.

Obviously the best solution is to harden the wired intercom system so it doesn't break. Nothing beats hardwired intercom in terms of reliability.

 

[joeyfergie]

Thanks for your input. I agree about hardening the clearcom. We rarely need clearcom in the pit however, and it happened to be a bad cable from another wall output to the beltpack. Unfortunately, we have a lot of old cables, and that was where the problem was.

Unsure if I completely understand what you are saying. You said that the clearcom is a two wire bidirectional audio signal. Are you referring to the clearcom port, or the headset port. My idea was to attach a phone/computer as a headset (still needing a beltpack). Our clearcom basestation has a headset port on it (4pin XLR), so I figured I would just attach the phone/computer to there (therefore not needing an extra beltpack). Based on pinouts I've found for Clearcom headsets, the mic and speaker audio lines are seperated. I would just be making a cable that would go from the 4pin XLR port (for headsets), and either split it to 2 TS connectors (audio in and audio out) for a computer, and/or a TRS(or perhaps a TRRS) for a phone (attaching to a phone the same way you would attach a headset to a phone). In both cases, a beltpack/basestation would be needed still for volume control and mic on/off, and the computer/phone would only be replacing the headset.

Unsure if this is what you were talking about in your response above or not.

 

[esmphoto]

I have built several converters like this (i can post a multitude of pinouts if you don't feel like looking them up)

lots of people try to get fancy by interfacing directly with the +30v and audio on the intercom line. I prefer to, as you suggested, use a headset connector on a beltpack, this way whenever I need to hook something up I can start with my standard go-to circuit which balances the speaker and mic IO in the 4pin to line level in out which i can convert as necessarily to talk to a recorder/player, two-way radio, computer, phone, bluetooth, etc. (also if I manage to fry something this way its just a beltpack not the whole comm system)

 

[joeyfergie]

So I am assuming what I am trying to do you have done and it works for you? Pinouts would be great if you have them handy.

 

[esmphoto]

Yep! and they have all worked well enough, included below is my cheat sheet of pinouts
(I dont have phone handset pinouts because every manufacturer's is different, what i recommend for going through a standard deskphone is adding a 2.5mm jack to the handset of the phone)

just take the IO from the beltpack and whatever you're interfacing it with and break them down to line level, then tie them together.

for low power speaker (as you'd find in these devices) to line that's as simple as a few resistors to sink off the extra power.

for line level to mic level you'll want to add some resistors and a capacitor to filter out the mic power from the source, attached is a diagram for a camcorder hookup from crown audio which can apply here as well.


***EDIT***
almost forgot, if you plan on building one box to move between different devices or are unsure of the values of resistors to use just shove in some 1k variables and you can fine tune everything once its hooked up

 

[museav]

So you are going to create a conference call with multiple phones calling into a 'master' that is then tied into the headset connection of a single beltpack or the master station? It may work in terms of audio but you would seem to have parallelled headsets with signaling, request to talk, volume, etc. all tied to the one physical interface. I don't know how you use your comms system but that would seem very limiting for many applications. Also, is the venue providing the phones are would you be relying on personal devices? If you are using personal devices then how will you address talk minutes, any damages, etc.?

 

[joeyfergie]

It wouldn't be a conference call. This would be a last minute solution in case we have a clearcom failure during/right before a show and this was the only option. Would also be used in case an outside person needed to talk to everyone on Clearcom in an emergency (ie, tech emergency and I (tech director) get called and need to talk to everyone). There would never be more than 1 other person on the phone line.

As for the phone issue, we have 2 lines at our theatre (one box office, one cast/crew). Currently only the box office phone is able to accept a headset (the cast/crew is corded), but I hope to change that. Also my cell phone (when I am there) is an option, as I have unlimited evenings/weekends (the only time that we would be using it anyways). Like I said, this is not something that would be used constantly on every show. In fact, I hope to nearly never have to use it. But after what happened in my last show (read first post), I want to have a backup in place.

To esmphoto: Thanks for these! I will take a look through them and start ordering the parts I need.

 

[museav]

Sorry, I took the comment "...or if we needed more beltpacks than we had..." to indicate that you were looking for something that could be used in place of multiple beltpacks.

 

[WooferHound]

What if you got a phone call into your intercom line wanting to know if you wanted to Change Your Long Distance Service ?

On a more serious note: If you tried to hook a beltpack up to a phone line. You would be connecting Both the Mic and the Headphone lines into the phone line creating a feedback loop. It would need to have some kind of switcher like a Speakerphone works.

EDIT
After thinking about this some more . . .
I think that if you could get a SpeakerPhone to autoanswer. You could modify it enough to provide a 4-pin XLR connector out to a standard intercom beltpack. Then you could plug this system into a landline and give your intercom system a Phone Number anytime you wanted to.

 

[esmphoto]

It wouldn't be a conference call. This would be a last minute solution in case we have a clearcom failure during/right before a show and this was the only option. Would also be used in case an outside person needed to talk to everyone on Clearcom in an emergency (ie, tech emergency and I (tech director) get called and need to talk to everyone). There would never be more than 1 other person on the phone line.

As for the phone issue, we have 2 lines at our theatre (one box office, one cast/crew). Currently only the box office phone is able to accept a headset (the cast/crew is corded), but I hope to change that. Also my cell phone (when I am there) is an option, as I have unlimited evenings/weekends (the only time that we would be using it anyways). Like I said, this is not something that would be used constantly on every show. In fact, I hope to nearly never have to use it. But after what happened in my last show (read first post), I want to have a backup in place.

To esmphoto: Thanks for these! I will take a look through them and start ordering the parts I need.

Glad to help! also, I use my system the same way, almost exclusively as a emergency/backup. this is not a real option for supplementing a comm system thats too small, but can be a show saving feature to have available if its needed.