[Elecraft] Modify an Astatic D104 Desk Microphone

[Jack Brindle]

At 3:34 PM -0500 7/2/04, Chuck Gehring wrote:
>I have an old Astatic D104 Desk Microphone that I would like to modify to
>use with a modern Transceiver.  Does anyone have some suggestions?

The D104 works quite well with the K2. There are a couple of ways to 
make the D104 match the input impedance of the K2. A 600 ohm - to-10K 
impedance matching transformer can do the job. A better solution is 
to use a small amplifier with high input impedance and low output 
impedance. One such amplifier using a transistor is described on the 
Elecraft Web page. I put together a circuit using an op amp based on 
a circuit from the 2003 ARRL Handbook. Op amps are perfect for this 
situation since they naturally have high input and low output 
impedances.

I almost forgot - my D-104 has the original G stand without the 
amplifier. If you have a stand with the amp built-in, then just hook 
things up, everything you need is already in place...

-Jack Brindle, WA4FIB
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