[Elecraft] D-104 preamp ...

[Paul Christensen]

> I have used the following circuit on a D104 to my K2:
>
> http://members.cox.net/n4jk/d104.htm
>
> Works great and you wire it for power through the mic connector.

That circuit won't work with the K3's bias on mic pin (Joe's intended use). 
To work that way with mic bias, power and audio must be joined on one 
conductor in the same way that an electret condenser element is powered.

However, the N4JK circuit will work when using the K3's +8V pin to power the 
nFET.   Also, in its shown configuration as a common-source (source 
follower) amplifier, I would eliminate the 100pF, 0.01uF input caps, and if 
absolutely necessary to kill static charge, increase the 2.7-meg shunt R to 
10-megs.  The common source nFET circuit is self-biased and no "gate leak" 
is necessary.  The rest of the circuit looks fine.

Paul, W9AC