[Elecraft] K2 Rev A - weak audio - one more time

[Eric Manning]

I'm one of many K2 Revision A builders who thought my audio was a bit feeble.

Well, it wasn't the audio at all - it was overall receiver gain too 
low - caused by the AGC threshold set too low and thus holding down 
the gain too much.

I tried a simple test from the instructions for upgrading to K2 Rev 
B. You tune to a quiet band - I used 28 MHz when the band was dead- 
and turn off the AGC by pressing AGC and PRE/ATT  together.
If the noise level rises, the AGC was reacting to noise and holding 
the receiver gain down when it shouldn't,  namely  when there is no 
signal present.

Mine rose between 1 and 2 S-units, by ear, when I turned off the AGC.

The fix is to replace R1 [51K] of the control board by a pot set at 
51K and then reduce the resistance  just enough to let the  noise 
level with AGC on approach or equal the AGC-off noise level.

If you turn R1 down way too much the receiver gain will fall way off.

If you turn it down a bit too much the S-meter LEDs will all remain 
dark when you try to re-set S meter HIgh and S-meter low, which you 
must do [manual p 84] . I turned it down just enough to bring up the 
noise level but not enough to prevent calibrating the S-meter. Just a 
small adjustment of the 100K pot I used.

Happiness - the receiver sounds much louder on weak signals and the 
S-meter is livelier.

I used a 100K trimmer pot soldered to little pigtails made from wire 
clipped from resistors, and I left it in the circuit, perpendicular 
to the board, with some scotch tape on the case to prevent it 
touching.
It's a tight fit but seems OK. Or, you can measure the pot value and 
put in a fixed resistor of same value.
-- 
Eric Manning   VA7DZ VE3DPV
K2 #2561 "Pauline"

If God intended you to use SSB, He wouldn't have given you a fist. Or 
two lungs.