How do I convert a CM-311A to wireless? (2 questions and replies)

Is it possible to cut the CM-311A mic cable off the belt pack, strip the cable, and solder on a transmitter connector?
K Karl

I have been using the CM-311A , for a year or so and love it. Is there a possibility of using this unit wireless, from the current body pack direct into a wireless body pack without buying another unit (CM-311AE) with the pigtail?
Brian Gerke

Reply: The Crown CM-311A headworn mic connects to a sound system by a mic cable. Some CM-311A users want to switch to wireless operation, but don't want to buy a Crown CM-311AE, which is designed for wireless use.
Here are three ways to make the CM-311A wireless.


Method 1: Cut the mic cable and connect it directly to a transmitter. In this case, the microphone might sound distorted because it needs at least 9 volts on the red lead. If necessary, you can wire a 9V battery to the red lead and shield, then connect the white lead to your transmitter audio pin and the shield to your transmitter ground pin.
Also, the CM-311A belt pack contains an equalizer circuit that makes the mic sound as good as it does. If the mic is wired directly to a transmitter, it won't sound the same, but you could EQ it at your mixing bo
ard. 
Method 2: Add the EQM-311 Module. Order the EQM-311 Module from your local Crown dealer. Cut the mic cable near the belt pack and solder the cable to the module. 
The EQM-311 Module adds some EQ to make the mic sound even better, and changes the transmitter's powering voltage from unipolar 3-9V to bipolar 9V. This eliminates distortion in the mic. The module has a pigtail output cable with leads for audio, power and ground. You solder those leads to a connector that mates with your wireless transmitter. 
The following document tells how to connect to various transmitters. Click here: Crown Technical Bulletin #3. Look for your transmitter model on the CM-311AE page.
Method 3: Connect the XLR connector of the CM-311A body pack to the transmitter input. To do that, you need to make an adapter cable. It's a 1-conductor shielded cable with a female XLR on one end and a Switchcraft TA4F connector on the other end (or whatever connector your transmitter requires).


Put a 4.7 uF capacitor in-line with XLR pin 2 (audio hot) to block DC from the transmitter, with the + side of the capacitor toward the transmitter. Solder the other end of the capacitor to the cable center conductor, and solder XLR pins 1 and 3 to the shield. On the other end of the cable, solder the cable center conductor (audio) to the transmitter connector's audio input pin. Solder the cable shield to the transmitter connector's ground pin.


For example, let's connect the CM-311A belt pack to a Shure transmitter. Let's assume you already made a cable with a female XLR on one end, and you're ready to solder the cable center conductor and shield to the Switchcraft TA4F connector on the other end. The TA4F is the small connector that will plug into the Shure transmitter's input jack.


Looking in Technical Bulletin #3, we see the connection for Shure transmitters. Solder the cable shield to Switchcraft TA4F pin 1, solder the center conductor (audio) to pin 3, and add a jumper between pins 4 and 3. (You might experiment with removing the jumper and see if it sounds better). Plug into the Shure transmitter, adjust the transmitter's trim pot for the highest level without audible distortion, and you're all set. If you still hear distortion, remove the connection to pin 3 in the female XLR.

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I've wired my CM-311A mic to an AKG transmitter and it doesn't work. The mic functions with the Crown battery pack so I know the mic is good. It doesn't have that inline electronic thing my CM-312AE had. Is that my problem?
Mark Boucher
Timmins, Ontario, Canada

Reply: To make the CM-311A mic work with a transmitter, you have two options:

1. Connect the CM-311A beltpack XLR connector to the transmitter input. XLR wiring: 1 and 3 = shield, 2 = audio (no B+ needed).

2. Order the inline electronic module EQM-311 from Crown's Parts Dept., and solder it to the mic without the beltpack. Also solder the module to a connector that mates with your transmitter. To order the EQM-311 module, call Crown at 574-294-8000 and ask for the Parts Department. EQM-311 module wiring: 
shield = ground, white = audio, red = B+.