[Elecraft] [K3] K3 2010 schematic

[Paul Christensen]

> Any chance of getting the old one archived out there?  I didn't look too
> terribly hard in the FTP server for it... But it would be nice to be
> able to compare and see how the enhanced mic audio and what not are done
> as the series 1uF caps from W9AC are still in place...

Brett,

On Rev. D of the Main DSP Board, mic coupling cap C28 was increased from 0.1 
uF to 1 uF.  On the alternate mic path, R24 and R26 were scaled from 1K to 
10K while keeping C36/C37 at 1 uF.   A 10x scaling increase in series 
resistance has the same net effect on the low-frequency turnover point as 
does a 10x increase in series capacitance.

Line In was affected the same way with an increase at R18/R20 from 1K to 10K 
while keeping 1uF of series capacitance.  The 10K + 1uF combination is good 
for keeping circuit Z and low-end audio response reasonable while minimizing 
SMT parts size and cost.

Paul, W9AC