Countryman EM6 with Clearcom?

[eslezak]

With my discovery of the Countryman EM6 system (combining the E6 mic with a Shure SE425/535 single iem), I have begun to wonder if it would be possible to use this system as a Clearcom headset. I know there are many factors to consider -- either re-wire or adaption to a 4-pin connector, mic impedance, need for phantom, etc. I am by no means an expert with electronics and circuits, but have built a few simple to moderate devices in my time.

If this turns out to be a viable solution, my plan would probably be to purchase an EM6 cable (as I already have the E6 mic, and am planning on purchasing some SE535's nearer to Christmas) with the TA4F Shure Wireless connector. I would then want to build some sort of small belt pack that would have TA4M & 3.5mm connectors for the headset, and a 4-Pin XLR to run to the Clearcom -- that could hold a 9v for phantom (hopefully that's all that would be needed), some sort of volume attenuation for the mic line going to the comm, and perhaps a push-to-talk button/switch. If I were to get real fancy, maybe a couple LEDs for battery level indication -- but that's getting ahead of myself. I know this is a rather expensive setup for a comm mic. However, the way I see it is that in ordering the TA4F connector with the EM6, I can use this for its intended purpose (mic/iem), and also have the option of having a very secure, comfortable, lightweight comm setup as well...

I still have a lot of research ahead of me, but if anyone else has thought about this or knows of a website that has collected this info together, I'd be happy to hear from you. Or any thoughts in general?

 

[Chris15]

At that level, a mic is after bias power (typically at a few volts) rather than phantom, the two ARE different.

Beyond that, looking at the threads for using a mobile phone headset with a real comms system should give you much of the legwork that will be needed in bringing this concept to actuality...

 

[jonliles]

Dramatech worked up the schemmies to be able to add a regular phone/pc headset (earphone and electret mic) to the CC pack (haven't had a chance to look at my telex pack to see if it would work). I Where a phone heas set all day (literally 8AM to 5PM) with no issues. Why buy a $300 mic when you can buy a $10 headset at your local big box?

See this thread

If dramatech is ok with it, I can email the schemmie to someone to attach to this thread...or maybe even sticky this thread and a couple of others together?

Dramatech's instructions:

The schematic is very simple and let me explain the methodology behind it. Before we start, I should mention that his will only work on Clearcom type beltpacks. That includes Production Intercom, Clear com and Telex systems that are made to work with the clear com powersupplies or their equivelant.
Perhaps we should start with a brief explanation of intercom systems. The earliest systems were built for Television and use the same principle as telepnone systems. They use a balanced 600 ohm pair that sees about 6 volts DC that is modulated as sound travels done it. The early Telex systems use this type of system. At about the same time that companies were building intercom systems for the theatre, Clear com came out with a different method. They use pin one of a 3 pin XLR connector for ground of sound or audio and power. Pin 2 supplies approx 30 volts DC to power the beltpacks, but has no audio on it. Pin 3 is the sound. As Clear com was the principle supplier of theatre intercoms, other companies copied their system so that various manufactures beltpacks could all be used together. Years later Telex purchased Clear com and RTS ( a very high end system) Telex maintained their original system, but also started building beltpacks that are compatible with clearcom. The easiest way to determine if a Telex system is compatible with the others is to measure with a volt meter, between pin 1 and 2. There should be around 24 to 32 voltsDC. If not, measure between pin 2 and 3 and if you get 6 to 15 volts with it fluctuating, then it is an older style Telex.

If your system is the Clear com type, then this circuit will work.

Looking at the schematic, you will notice that there are two resistors connected to pin 2 of the "Party line" XLR that is a 3 pin and there is a female and a male connector. It makes no difference which connector you connect to. The purpose of the connection is to get power for the circuit and to provide "Phantom Powering" to the electret microphone. The reason for the two resistors, is to break the voltage down to what the microphone wants to see. The 100K resistor is to get a large drop and the 10K is to adjust the finer voltage. By using two resistors instead of one, there can be fine adjustments made with the smaller resistor. One way to make that adjsutment is to measure the electret mic connections, while it is in use, on say a computer. Then when it is connected to the conversion circuit you can measure the voltage again and see if it is close to the same. In the case of the two different brands of cheap headsets that I have used, the 10K is close enough. Once the electret mic is powered, it will produce an audio signal. In order for that signal to enter the belt pack, it must insure that the Phantom voltage can not continue into the input of the beltpack audio signal for the microphone. As a capacitor will not pass a DC voltage but will allow the audio, C1 is a 10 microfarrad capacitor rated at least for more than 16 volts. The ones I used are 10uf@25v. The positive end of the cap is connected to the powered side and the mic connection from the electret mic. R4 serves as a gain control for the microphone. In my case I used a 10K 20 turn variable resistor. The value can be almost anything from 5K or greater. The higher the resistance the more accurate the turning of the control on the variable resistor. The variable resistor wouldn't work very well by itself, but by adding R3 from the audio line to ground, it becomes an "L" pad and makes the R4 variable resistor work. All of these parts are available from Radio Shack. The resistors are 1/4 watt. I soldered some of the components directly to the back of the pins on the 3 and 4 pin XLRs and soldered the rest of the components to each other, and hot glued them to the ones that were the closest connection to the XLRs, so that hey had some strength against movement.
For my connectors for the Electret headset, I used mini XLRs such are used on Shure wireless mics. You could use DIN connectors, at a considerable less cost. The only problem with a DIN connector is that it won't lock in place. I purchased my headsets from mpja.com, I paid a bit over a dollar a piece for them. mpja.com also sells DIN connectors and soldering irons at a very affordable price.
The only problem that I have had is that the cheap electret headsts do not have noise cancelling microphones. It becomes really important to keep the mic turned off when not in use.

The schematic is attached as a pdf file. I am sure that you will have many questions so just email me as you need. I have some pics that i will send later.

 

[dramatech]

No problem, you can post the schematic. I should say up front, that there will be those that will have many comments about my schematic. It is just a simple solution that has worked well at my theatre for about 5 years with no problem. There are probably improvements that could be made.

dramatech
Tom Johnson
Florida's Most Honored Community Theatre

 

[Chris15]

The schematic under discussion:
View attachment Electret headset conversion schematic.pdf