Revisting audio after absence from the reflector

[Tim Logan]

*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



*
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[Steven Pituch]

Hi Tim,
I brought up this question a few months ago.  On say 40 meters with a narrow
filter setting I noticed I needed the preamp on to hear very weak signals.
Of course using the preamp on 40 meters made the signal harder to hear so it
was a catch 22.  I read all about squeezing a little more audio out of the
rig, but it seemed that the K2's audio was already optimized.

Then by chance I took off my old Heil Pro headset, and put on my cheap RS
Novus 71 headphones and I found that I had too much volume!  I took the
preamp out on 40 meters and could hear the Fox perfectly.  By comparing the
headphones side by side, in this case, the Heil set seemed to have an audio
notch at about 600 Hz.  I could hear the static around it but not the zero
beated signal. Raising the volume just increased the static.

So now I have plenty of volume by just switching headphones.  And its at
like 9 o'clock now instead of max.  Now in retrospect, I would think unless
one is partially deaf you would never need more volume than the K2 can give.


So try some other headphones first. Maybe the impedance match is not good
enough.  My second resort would be an external audio amp box with two
outputs so two people could listen at the same time.

72.5,
Steve Pituch, W2MY

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[Don Wilhelm-3]

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

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