Using a pair of headphones as a ClearCom headset?

[petercav17]

Hey all.

We are on a shortage of working headsets at my theater and my friend, who recently bought a nice pair of Sennheiser headphones (with a built in mic for use with a phone) had an idea to create a female 1/8 inch to male 4 pin XLR adapter so he could use his headphones with the ClearCom belt packs. My question is this - would it work? Just an adapter with the correct wiring? I'm afraid that 48VDC might damage the headphones. I am also concerned that the mic would not be compatable with the ClearCom system but it seems like it would be simple..

Thanks for any insight.

 

[NewChris]

I looked into this at one point also. I never tried, but you need to make sure the resistance of the headphones match the clear com headsets.

 

[n1ist]

I've done it with a cheap pair of PC 'phones. It worked fine. I also added a battery, 2 resistors, and a cap to use the mic as well. Much more comfortable than the standard headsets.
/mike

 

[MrX]

I've done this many times. Usually (always?) the mics in these headsets are electret and need power. Use a beltpack that supplies this power (they'll have an "electret" mode) and it'll work fine.
Impedance of the headphones doesn't matter, btw.

 

[MikeJ]

You need to check the power range of the electret mic in the headset first. Most clearcom or PI units are 24-30v, however some electret mics have a voltage limit of ~12volts, so you may need to drop the voltage for the mic. IIR most cell mic have a range of 3-12 volts or somewhere in that ballpark, so something like an L7805 will give you 5 volts for the mic. This is the same thing that is in most cheap cigarette lighter-to-USB chargers use. I think 30v is on the high side for these regulators, but its probably worth a shot if needed. It should fit into an XLR connector with a little effort. Its probably best to mount it to the chassis of the connector as a heat sink.

You can also make an adapter the uses a separate 9v battery to power the mic, which might be simpler.(I think someone makes these already.)

 

[MikeJ]

Oh, By default Clearcom does not use electret mics, only dynamic, hence the adapter. MrX mentioned there are some pack available that offer power for an electret mic, but they are not the standard pacs you usually find.

 

[MikeJ]

Clear-com makes an adapter for 2.5mm cell headsets to 4 pin xlr, I cannot find the link at the moment.

I also could not find the 9v battery adapter, but there is a DIY solution, post #7, I would wire this to a female connector, rather than modify your headphones.
I'm not sure, But I do believe that the capacitor used for decoupling should be Bipolar, not the polarized one shown. So it will block DC, but still pass audio(AC)
Someone who knows something about electronics hopefully will take a look, an confirm or deny my observation.
http://www.controlbooth.com/threads/homemade-clear-com-headset.17252/

I've done it with a cheap pair of PC 'phones. It worked fine. I also added a battery, 2 resistors, and a cap to use the mic as well. Much more comfortable than the standard headsets.
/mike

Mike you seem to know whats up, can you detail your solution, and take a look at the setup in the old thread too?

 

[petercav17]

Awesome, thank you guys for the help. I'm looking at parts now. I think I'm going to follow with the battery option that MikeJ led me to.

 

[petercav17]

Just remembered something: We used to have a Production Intercom system. However, the base station broke and we upgraded to a ClearCom base but we have all PI beltpacks. There is an adapter on the base station which I think might change the pinout? Our new clearcom belt packs don't work right with the system, so we don't use them. Not sure if this would be why or if that is even a thing. I'll have to examine the system more closely. Is it possible that the PI beltpacks/headsets have an electret mic?

 

[MikeJ]

Production intercom(now Pro Intercom) and clear-com should be completely compatible with each other. By this i mean the common party line systems, they are either 24 or 30volt, but work fine together. Both use dynamic mics only, by default. There are other digital systems, like clearcom Helix, that do require adapters, but i doubt that is what you are dealing with.

Pinout should be the same with either base station and/or beltpacks.

What model packs and base station do you have?

Also I will double check that battery powered adapter tomorrow to make sure it will work correctly. The original post reports that it works fine, but I want to look into it further. Some mics will take the full voltage, like aviation headsets, but consumer stuff like radio mics often wont. You can run any condenser mic at lower voltage, but you reduce the maximum input before clipping. In most cases 5-12v will be plenty for clear-com, but it could hit its limits in very loud concerts and such. Have to try it to find out.

 

[MrX]

Unfortunately, there's a lot of misinformation and bad advice in this thread.
All modern belt packs support electrets directly with no need for external circuitry.
Clear-com, telex, Pi all have electret mic modes.
RTFM for details.

 

[MikeJ]

MrX, I just looked up the specs on Pro intercom. They do indeed list electret mics 1.2-1.8k ohms as supported, However Production intercom pacs from about a year ago, before the name change, do not have the electret option.

 

[MikeJ]

I would like someone to confirm, but it looks like either bipolar or polarized capacitors will work in this application, as long as the + is facing the right way like in the diagram.

 

[MrX]

MrX, I just looked up the specs on Pro intercom. They do indeed list electret mics 1.2-1.8k ohms as supported, However Production intercom pacs from about a year ago, before the name change, do not have the electret option.

When I checked, I was looking at the new ones.
http://prointercomllc.com/wp-content/uploads/2013/12/Ins_BP1SL_PRO.pdf

 

[petercav17]

MrX, I just looked up the specs on Pro intercom. They do indeed list electret mics 1.2-1.8k ohms as supported, However Production intercom pacs from about a year ago, before the name change, do not have the electret option.

Yeah, the packs we have do not have that little switch on the bottom that allows compatibility with an electret mic.

 

[MikeJ]

When I checked, I was looking at the new ones.
http://prointercomllc.com/wp-content/uploads/2013/12/Ins_BP1SL_PRO.pdf

Yep, the new ones do have the option, which actually solves all of the problems, if you can get a newer pack. Most "legacy" clearcom and PI gear does not have the option though. If you are working with a system that is a few years old, or older, than some modifications may be required. I have access to some electret mics modified to be used on clearcom/pi, but Ihave not had a chance to look at what was done to them. Hopefully I can get to that this week, and report back to this thread.

Some new packs including the HelixNet from clearcom, do have 2.5mm jacks for use with phone headsets. There are also Bluetooth adapters available.

 

[MikeJ]

Also just to clarify, Production Intercom/Pro Intercom uses 24 volts, Clearcom used 30 volts. They are both completely compatible with each other. You may notice a small difference in the sound of your own voice being sent back to you'r headset, but this is adjustable on the beltpack, and does not change the the way your mic sounds to other people. The newer digital HelixNet from clearcom is NOT compatible without an adapter card in the base station and runs at 60 volts; It will fry conventional 24-30v com without the adapter.

Helix is awesome though, and DEAD SILENT, when no one is talking. When you first use it, you will think that the com is not connected or broken(several times during a show), because it is that quiet.

 

[MrX]

Yep, the new ones do have the option, which actually solves all of the problems, if you can get a newer pack. Most "legacy" clearcom and PI gear does not have the option though.

Legacy? How far back is legacy in Pro Audio? 5 years? 10 years?
The Clear-com 500 and all later beltpacks have the option, from 1996, 19 years ago.
The Telex BP-x000 series and later have the option, made from 1997 on, starting 18 years ago.
It's only the PI stuff that didn't get it together until recently.