[Elecraft] D104 mic

[Don Wilhelm]

Chris,

Unmodified, it will probably sound terrible (very 'bright with lots of 
highs, weak lows), but with a bit of work, it will sound great - just 
like Astatic intended.
The D-104 element is either crystal or ceramic, and wants to work into a 
high impedance (like the grid of a vacuum tube with a 1 megohm 'grid 
leak' resistor) load.  Modern transceivers present a much lower 
impedance load (nominally 600 ohms).

I have seen some comments that the simple insertion of a 1 megohm 
resistor in series with the AF line is all that is needed.  That may be 
the first thing to try.  I strongly suggest you use the K3 monitor 
function with the K3 in TEST mode and record your audio on the computer 
- listen to the recording to see what it sounds like (that is almost 
impossible to judge while listening

With a single FET buffer  or an op amp between the D-104 and the K3 (or 
any other transceiver), the D-104 will "come to life" just as it did 
with the old vacuum tube rigs.

An op amp solution is a natural because the characteristic of an op amp 
is very high input impedance and low output impedance - perfect for the 
D-104.  An LM358 wired as a unity gain buffer should do the job nicely, 
and for the voltage swings involved (small) the LM358 can be powered 
from the +8 volts available at the front microphone jack pin 6.  If you 
would want to use the rear microphone jack, the FET solution would be 
better because the voltage to drive the FET can be supplied by turning 
bias on.

I am not going to give you a circuit diagram because I have not 
developed and tried it out.
There is another solution - that is to replace the original element with 
an electret element, or with a Heil HC-4 or HC-5 element (Heil offers a 
kit for that).

73,
Don W3FPR

Chris Hembree wrote:
> Anyone ever use a D-104 (non amp) on a K3. How does it sound?
> Chris W7CTH
>
>