[Elecraft] K3 Turn on Pop(WAS K3 Audio)

[Paul Christensen]

> Hrm.  Oh well.  I do think that the audio section would benefit from a
> rejiggering of quite a few of those caps for more LF.

On the Rx side, there's not much left to consider after the DAC --at least 
what I can see on the schematic.  The circuit path is pretty darn simple. 
However, the cap fix we've been discussing is really only part of the cure 
toward establishing a flat low-end receive response to 100 Hz or a bit 
below.  I still see the same effect as measured by Alexander in his link 
below:

http://forum.cqham.ru/download.php?id=44172

There's additional low-end roll-off not attributed to the coupling C after 
the DAC (again, based on what I see on the schematic).  So, the question is 
"what is causing the remaining roll-off starting around 400 Hz?"  To 
compensate for what Alexander and I are measuring, I need to boost the Rx EQ 
Band 2 by about +10 dB to get something remotely close to flat between 
100-200 Hz.  Also, I do not see where Band 1 (50Hz) changes the receive 
audio response.  It's almost as if it's deactivated or something in the 
analog and/or digital path is causing a sharp HP effect above 50Hz.  No 
amount of cut or boost on Band 1 brings about change on my K3.

On the TX side, there are additional C values (or if you prefer, R values), 
that can be scaled to your liking.  I've discussed some of those component 
size changes on the N1EU website.  Also, I believe the newer main K3 DSP 
Boards may now have re-scaled R values along parts of the affected Tx path.

Paul, W9AC