Posted by
Mike Morrow-3 on
Jan 09, 2015; 6:48pm
URL: http://elecraft.85.s1.nabble.com/K1-AF-sidetone-loudness-problem-tp7596933p7596941.html
Roland_DF1OE wrote:
> Last Year i built my k1 #3310...
Excellent choice!
> I ve a little problem - may be it is quite normal...
What you describe below is very abnormal.
> during sending cw the sidetone is very very loud - louder as it is during
> adjusting ST_L and much louder than testing it with no cw HF transmission.
>
> During transmission it gets louder after a time. Even if i put ST_L to 1
> (one) i get a loud sidetone during cw hf transmission.
My first guess would be some disturbance at front panel board FP-U2,
the DAC which actually produces the sidetone. The DAC uses Vdd from
the 6.0 vdc regulator FP-U4 as its reference voltage. Perhaps you
have some RF intrusion or regulator load change during transmission
that is upsetting the regulated Vdd at pin 7 of FP-U2 that is coming
from regulator FP-U4.
Such regulators can become unstable if there is not a small capacitor
on the output, although the ZR78L06 is not supposed to need one.
Regardless, the FP board has such a capacitor (FP-C5, 0.01 uuF) mounted
on the "bottom" (back or rear) side of the FP board. I would check
that it is in place, and properly soldered.
FWIW, here's the MAX518 data sheet:
http://datasheets.maximintegrated.com/en/ds/MAX517-MAX519.pdfOf course, perhaps it is something completely unrelated. But it is
definitely abnormal. This is what I'd check first.
73,
Mike / KK5F
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