Posted by
Don Wilhelm-3 on
Aug 28, 2005; 8:19pm
URL: http://elecraft.85.s1.nabble.com/EV664-tp381491p381504.html
Fran,
I will not say that one is better than the other, but Jim's change only
deals with the mic input itself, while Stewart's change also deals with the
internal behavior of the Speech Compressor chip by changing C31 and resricts
the low frequency fed to the Balanced Modulator by the Speech Compressor
chip by reducing the value of C20.
Both agree that the value of the input capacitor C34 should be reduced.
Jim's change in the R14 resistor value may provide a better match for the
pro-audio mics that he is using, and as such may be highly dependent on the
mic actually in use. Changing R14 to a higher value has been a favored
change for those folks using low output mics (such as the Heil HC4/5 element
mics) for some long time now - R14 is usually changed to somewhere in the
range of 5k to 10k for use with the Heil elements and no additional
amplification.
Your mileage may vary, and is likely dependent on your particular mic. In
the old 'spirit of ham radio', a bit of experimental work may be a worthy
endeavor, but then, if you don't have the tools to properly evaluate your
efforts, it may be better to leave the design 'stock' - not everyone's mods
belong on all K2s - special situations do exist, and they are discussed here
too.
73,
Don W3FPR
> -----Original Message-----
>
> I am now confused by the existence of two different mod's with the same
> goal.
>
> It makes perfect sense to me that I should not be wasting Tx
> energy on audio
> frequencies as low as 20Hz. Beyond that I am somewhat in the dark.
>
> Jim Brown and Stewart Baker have each suggested a modification to improve
> this situation.
>
> I am at a loss to know which, if either, I should implement. I must admit
> that I an very tempted to incorporate the indicated improvements.
> However,
> I would have no means of evaluating the results and therefore look to the
> remainder of those on this list for further opinion.
>
> Summary of the mod's are:
>
> from Jim:
> Change R14 from 1K to 2K.
> Change C34 from 2.2hF to 0.22 uF.
> Add 1uF in parallel with R15
>
> from Stewart:
> Change C34 from 2.2uF to 0.47uF
> Change C31 from 2.2uF to 1uF
> Change C20 from 0.33uF to 0.047uF
>
> Is the situation severe enough to warrant an official mod for this?
> Inquiring minds want to know.
>
> Fran
>
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