[Elecraft] [K3] Fw: Non Amplified D104

[Paul Christensen]

> Did you use the K3's MENU:MIC SEL option to choose high gain for the
> microphone input?

Good advice from Ron.  After checking that, and assuming the mic is 
relatively old and its past quality-of-life unknown, I would consider 
replacing the D-104's mic element with a similar crystal element from 
Mouser:

http://www.mouser.com/catalog/specsheets/KT-400023.pdf

Price in small quantities is USD $4.77.

If you use a single-transistor FET buffer, be careful of the various designs 
and mods seen on the web.  Some utilize unnecessary components at best, and 
performance-degrading parts at worst.   If an existing 2-stage Astatic 
buffer is used, one can place a resistor in series with the mic lead, > 1 
megohm in value and make up the gain with the amp's level pot although it 
may become unstable and certainly noisier than a well-designed single-stage 
FET circuit.  Either circuit can be powered from the K3's mic connector 
through a current-limiting resistor.

The existing input Z of the Astatic pre-amp calculates to ~ 470K-ohm and 
although it may seem high, it's just not high enough for a crystal element 
to achieve a reasonably flat response down to 80-90 Hz -- the first 
fundamental of most male voices.  My D-104 achieves this with the K3 in ESSB 
mode, although I'm not sure if all of the extended low-end can be captured 
in the K3's default SSB Tx setting.

Paul, W9AC