[Elecraft] Revisting audio after absence from the reflector

[W3FPR - Don Wilhelm]

Tim,

I am one of the folks who have said the K2 audio is low - BUT
The fact is that one of the K2 design objectives was for low battery drain, 
and that dictates limits on the audio reserve power available.  The K2 audio 
is adequate, but by comparison to most other transceivers, it is low.  An 
external audio amplifier is a good solution, particularly if you are 
operating in a high ambient noise environment or want to operate (say) at 
Field Day with the speaker (non-battery class of course).  I use Tom 
Hammond's amplifier with a 9 ohm speaker here and it has LOTS of output, 
even though its full power output will only be realized with a 4 ohm 
speaker.

As for the differences between your 2 K2s, I can recommend that you check 2 
things - first is the winding of T7.  The old turns ratio was 11:3 while the 
new ratio is 20:5.  This sets the impedance that the variable xtal filter 
sees and could be even be optimized for you particular set of xtals if you 
want to experiment.
The second thing that will make a difference between different K2s is the 
AGC level.  The AGC and the RF gain  both feed the AGC input of the IF amp 
chip, so that level is crutial to the overall gain of the K2 receiver.  In 
working on several K2s, I have noticed sthat there appears to be a slight 
difference between receivers that is quite sensitive to the AGC voltage. 
The 3.8 volt setting mentioned in the manual is not graven in stone, so feel 
free to change the AGC threshold to match the perfomance that you want - I 
usually find that somewhere in the range of 3.6 volts to 3.8 volts is the 
optimum setting.

73,
Don W3FPR

----- Original Message ----- 

> *Hi folks -
> In anticipation of beginning my next K2 I have been reviewing the archives 
> for the many, many posts on audio - so please forgive one more! I've built 
> two K2's and owned 3. The one I am building now will be my 3rd. The only 
> thought I've ever had as a "negative" about K2's is the audio volume. At 
> one point two of mine seemed to have different relative volumes - even 
> though Gary checked out the lower volume one and said it was A-OK. 
> SO...in building another one I would like to ask three questions for those 
> of you WAY more informed than this dim bulb :-)
>
> 1 - During my build, can you suggest particular building stages and 
> components where I should go beyond the normal voltage/continuity checks 
> from the manual to make ADDITIONAL measurements to make 120% sure I have 
> not inadvertantly "built in" anything that might contribute to a lower 
> than standard volume?
>
> 2 - Have there been or are there any suggested component substitutions 
> that might increase overall audio? If so, what are the tradeoffs for this 
> experimentation?
>
> 3 - I note with interest Tom Hammond's circuit for an external amplified 
> Motorola speaker (see http://N0SS.net) - has anyone adopted and used this 
> particular setup and what do you think? Does the amplification have any 
> negative impacts (distortion, increased noise, etc)?
>
> If I missed archived responses that previously addressed these questions, 
> I apologize in advance!!! Thanks folks!
> 73/Tim NZ7C