[Elecraft] D-104, only slightly OT

[Ron D'Eau Claire]

Paul, W9AC, wrote:

Also, anyone contemplating the use of the D-104 with the stock Astatic amp 
should consider an alternative buffer amp.  The input Z to Astatic's 2-stage

preamp calculates to 470K-ohm -- way too low for a crystal cartridge.  The 
crystal cartridge should see a termination of no less than 5 megohm, and 
preferably greater than 10 megohm in order to preserve reasonable low-end 
response.

---------------------------

The Astatic D-104 was designed as a *communications* microphone with a
carefully shaped frequency response for speech and not for extreme high or
low frequency response. 

The graph of the audio response published by Astatic, using the built in
amplifier, shows 0 dB at 1 kHz. Below  1 kHz the output drops off smoothly
to -5 dB at about 200 Hz, then more steeply down  to -10 dB at 100 Hz where
the published curve ends. 

That roll-off is important since excessive low frequency response robs a
signal of intelligibility and "punch" since the bulk of the energy, but
virtually none of the modulation in the spoken voice is down in those
ranges. 

Above 1kHz, the output rises smoothly to a peak a bit above +10 dB at 3 kHz,
the smoothly drops off to almost - 20 dB at 10 kHz. 

That rising characteristic to a peak in the roughly middle point of the
speech audio spectrum is what made it so effective in communications and
made it so popular. 

Ron AC7AC