On Sat, 29 Aug 2009 20:08:35 -0700, pfizenmayer wrote:
>The headphone output IC in the OII is a stereo IC LM4811.
Thanks for the detailed analysis, Hank. That's pretty much what I
expected. Consider the output stage a constant voltage source with
27 ohms in series. In general, output stages don't want to be
heavily loaded, but that 24 ohm resistance provides pretty decent
current limiting. I'd say that any headphones having an impedance of
20-200 ohms ought to work great, and higher Z phones may not be loud
enough.
HOWEVER -- your analysis and mine ONLY looks at the output stage. As
someone else noted, there is probably a GAIN problem between the
audio detector and the output stage, and THAT's why there's low
audio on phones. It makes sense to me that it might need to be fixed
in the software/firmware that tells the DSP what to do.
If this were Elecraft, we'd have a fix in a week or less once the
problem was identified. But this isn't Elecraft. :)
73,
Jim Brown K9YC
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