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Date: Sun, 2 Sep 2001 01:02:36 -0700
From: "IronMan Mike Curtis"
Subject: Carbon mic for harp

No it's not a question - it's a statement.

I've picked up a couple of 1940/50 Shure 102 series carbon hand mics,
and converted one for harp. They're made of cast metal, and are
tough as nails. Carbon elements are nearly indestructable.

These use carbon elements, which require a power source. The carbon
button works as a variable resistor. I'm currently using a 9 volt
battery and a 1k fixed resistor for testing purposes (and because
that's what I had handy ;-) It has a really unusual sound, a little
more mids and smoother than controlled magnetics, and more "natural
distortion" than a JT-30. Of course, this could be due to the
*extremely* high output.

I'm going to try a design using lower voltage. I don't need it
nearly this hot, and with lower voltage my batteries will probably
last a LOT longer. I'm shooting for 1000 hours or thereabouts. I'm
estimating that I will probably get around 40 hours from a 9 volt
alkaline battery. The carbon element sounds nicest with a 5 mA draw,
although the spec sheet talks about 50 tp 100 mA (entirely too much
for battery operation). I also want to use a transformer instead of
drawing the signal across a resistor. The carbon element is rate~br>100-200 ohms operational impedance, and I want to bring this up to
around 50k or thereabouts. This will step up the output voltage
considerably, another reason to cut the raw output.

I'll keep everyone posted - and maybe I'll start selling these as
custom mics. They're indestructible (in fact, the "official" Ma Bell
fix for low output on a carbon mic - they used to be standard
equpment for phones - is to drop it from shoulder height onto a
concrete surface!)

BTW this information will be useful for those who want to cut the
mouthpiece off an old Ma Bell handset and use it as a harp mic.

- -IronMan Mike Curtis LIVE video of Mikes #1 MP3 hit PLAY THEM BLUES
Featuring a C diatonic harmonica solo in 7 different keys (G, A, B, C, D, E,
F)
http://bumpngrindrecords.com/ironman_play_blues.ram
Order IronMans CD-get a FREE vacation! http://www.bumpNgrindrecords.com