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From: lagasse@biomed.UUCP (Robert C. Lagasse)
Newsgroups: net.aviation
Subject: M-87 Microphone mod
Message-ID: <123@biomed.UUCP>
Date: Fri, 13-Sep-85 09:34:39 EDT
Article-I.D.: biomed.123
Posted: Fri Sep 13 09:34:39 1985
Date-Received: Mon, 16-Sep-85 00:20:23 EDT
Organization: Mass. Gen. Hosp. - Dept. Biomed. Engineering
Lines: 15


   In a previous article, Paul Kube asks about using a 5 Ohm microphone with
modern systems which are at a much higher impedence.  The answer that I
can provide is probably not useful, but....  It might be easier to find a
new microphone element that is of an impedence that matches your radio set
if the old one can be surgically removed neatly , and the new one of a
(hopefully ) smaller  physical size implanted.  A new element is bound to be
smaller than the one in a vintage headset.  Matching impedences through a
transformer will introduces some losses which may not be tolerable without
additional amplification.  A small audio transformer with one of the
windings at a 5 ohm impedence is an animal I have never seen in any of my
many catalogs.  If you could find one, additional amplification is no big
deal and could be added to the headset at the earphone area and potted in
place witha resin, or it could be added to the guts of your radio set. You
might want to post your original question in net.analog which will no doubt
unearth the audio gurus.


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