small microphone element -- non-electret?

- P
- Percival P. Cassidy
  
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posted
15 years ago

Sun, Sep 14, 2008 9:22 PM

My mother-in-law spilled something on the handset of her CrystalTone amplified telephone, and the outgoing volume level is now pathetic; i.e., the people she calls can hardly hear her, even with the "boost" button pressed.

The mic element looks pretty much the same as the electret ones sold by Radio Shack, but I cannot detect a sufficient polarizing voltage for an electret -- just 0.7V.

The only two mic elements RS lists are electret, and I have been unable to track down any mic elements of a similar size that are not electret.

Any ideas?

Perce

- M
- Michael A. Terrell
  
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posted
15 years ago

Sun, Sep 14, 2008 9:27 PM

Disconnect the old microphone and measure it again. All it takes is a slight tracking across the electret, and the current load will go up and pull the DC supply low. The preamp is a FET and will work at a lower voltage than a bipolar amp.

BTW, this type of question belongs on news:sci.electronics.repair

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- S
- spambh
  
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posted
15 years ago

Sun, Sep 14, 2008 10:14 PM

The first thing that must be done when this happens is shut the power off immediately! If left on and the liquid is conductive, things start to corrode quickly and it won't take long to chew up tiny conductors (bigger ones take longer). Examine things closely (magnifying glass), looking for corrosion. If you find it, clean it off (soap and water and brush), dry things off and whatever physical damage that has occurred must be repaired by soldering in bypassing wires, etc. Assuming all this is done, and physically at least, you are back to square one, it is likely that the mic is an electret and whatever polarizing voltage was being supplied is no longer there due to electrical damage. You could remove the mic. and try treating it as an electret in a separate mockup and see if it works.