help identifying +/- terminals on capsule

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pond

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Jul 18, 2018
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Picked up an old grundig gdm121(sennheiser md21) that is wired as unbalanced high impedance 3pin DIN.

I would like to convert it to balanced low impedance XLR, and found the following information:
http://nobsinn.powerbone.de/techniktipps/sennheiser_md_21-gdm_121/

I think this is probably a very noob question, but are the two wires coming from the capsule the positive and negative connections? or are they both positive and i need to solder to one of the wool covered terminals, or the one with the plastic tubing hanging off it?
btw, what is the purpose of that tube?

thanks for reading

 

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pond said:
are the two wires coming from the capsule the positive and negative connections?
Yes, definitely. They should go to pins 2 and 3 of the XLR. I would think the red one goes to pin 2, but you need to check the polarity by comparing with a mic of known lineage.
 
So... Went to my girlfriend's dad's house today and we desoldered the transformer and changed the 3pin DIN to an XLR.

Multimeter across pins 2 and 3 hovers around 198ohms. Pin 1 to the microphone body shows continuity.

Plugged into the preamp however it produces only a very very small output. If I yell into the mic with 56db gain I can record a small signal.

Is there any other tests I can perform to confirm whether the capsule is working?

Thanks
 
pond said:
So... Went to my girlfriend's dad's house today and we desoldered the transformer and changed the 3pin DIN to an XLR.

Multimeter across pins 2 and 3 hovers around 198ohms. Pin 1 to the microphone body shows continuity.

Plugged into the preamp however it produces only a very very small output. If I yell into the mic with 56db gain I can record a small signal.

Is there any other tests I can perform to confirm whether the capsule is working?

Thanks
Could be the voice-coil is stuck; this can unfortunately happen to a mic that age. Can you see the VC and try to make it move?
 

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