How to get rid of the ECM-55B power module ?
 

I’m trying to get rid of the power module of the ECM-55B in order to connect the mike directly to a MD recorder (with plug-in power). I was also thinking about using this configuration with a wireless transmitter (mini-XLR plug for example). The power module is bulky so I would rather prefer to only have the MD recorder and mike.

After opening the module, I was able to see 3 lines going to the capsule : red, white, shield. There is a potential of 1.5V between the red and shield … so I’m assuming this is the bias voltage to power the capsule. The white goes to the transformer so it must be the mic output.

So I just disconnected the 3 wires of the capsule and made some tests with a Sharp MT-821S MD :
- Shield -> sleeve of the jack
- Red -> tip of the jack
- White -> tip of the jack through a 2uF capacitor to remove the bias voltage.

It didn’t work… hum and very low signal.

How is a ECM-55 for RF transmitter different from an ECM-55B with the power module removed ?

Any idea on how I can solve this problem ?

Thank you
Dany

I don't understand why you used the capacitor.

The capsule needs the 1.5 volts for power and the cap blocks it. At least it does if I understand your wiring description.

From my observations, the ECM55 capsule has 3 wires : shield, power and audio out.

But the MD microphone input has only 2 lines (gnd and mic in) and combines a plug-in power (bias voltage over the mic line). That's why I've connected the mic input to the power line of the capsule.
For the audio out from the ECM55 I've used a capacitor in order to remove the bias voltage from the mic input line of the MD.

Impedance problem ? I'm confused....

I'd bet that the microphone is balanced with a shield and the two non-shield wires are the two balanced signal lines, one of which should be connected to the signal in of the MD recorder, the other of which should be connected to ground. Let the shield just float unless it isn't common to either of the non-shielded wires. If it isn't it could be connected to the ground connector too.

But that's just a guess without playing with the setup.

The DC bias volts obviously don't hurt the MD recorder and I'd bet they don't bother the capsule either.

But that's not me with an expensive capsule right there.

Yes the microphone is balanced AFTER the power module.

There is a transformer inside that provides the balanced audio.

When I looked at the little PCB contained into the power module I could see the white line (audio out from capsule) connected to the transformer and the shield closing the circuit. The red line of the capsule is connected to the battery (+1.5V) so I don't think the capsule itself is balanced.

dany

Hmmmm. Interesting.

What happens if you connect the red and white lines together and to the tip of the microphone jack with the shield competing the circuit?

Course maybe you don't want to be a test pilot here given the cost of the ECM-55. :-))

How about incorporating the transformer into the hookup you are making? Use the transformer between the white and shield and allow the other side of the transformer to sit across ground and signal input. That will effectively remove the voltage from the white lead and allow you to connect the red lead to the recorder side of the signal lead.

Another path might be to ask Jay Rose over on www.dv.com. He writes the column on sound for them and is pretty good with circuits as well as mixing sound.

Lectrosonic website had the solution.

Red -> Tip
White+Shield -> Sleeve

I'm preparing an article about my ECM44/55 modification. Basically it's about cutting the cable and adding a mini-XLR 5-pin connector so you can make your ECM-44/55 more universal :
- ECM-> Power module (for phantom/batter powering)
- ECM-> Mini-Disc (get rid of the power module for lightweight configuration). MD provides the necessary bias current. I couldn't live with the bulky power module+XLR cable...
- ECM-> Wireless transmitter (having the 5-pin mini-XLR makes the ECM now compatible with Lectro and Azden UHF transmitter... sweet ! (no excuse for not renting one).

Dany

Check with Jay Rose over at DV.com