On Wed, 2008-03-05 at 17:12 -0500, Rick Denney wrote:
> Dr. Gerald N. Johnson writes...
>
> > It would also be great to measure as much about the performance as
> > possible (MDS, S/N, blocking range, audio bandwidths, gains everywhere)
> > before and after the project to see if the benefit I expect is really
> > there. And to write down perceptions, as some of the improvements may be
> > subtle.
>
> I'm hoping that doing so will address an audio quality issue that I
> have on my V. When I turn the AF knob past about 8 or 9 o'clock, the
> audio amplifier clips, as we've discussed before. Using a clean
> external headphone amp to equalize normalize the amplitude, I've been
> able to observe that clipping on my scope. I can turn it way down, and
> turn the external amp up, and there is no clipping, though the audio
> noise floor rises, too (usually to no ill effect because of band
> noise).
>
> Maybe it's the issue of the AF pot needing a higher series resistance,
> or because an audio mod that had been done on mine was undone, as were
> both suggested when I brought that issue up.
>
> Also, when I turn off AGC, the audio problem gets much worse, though
> this is a function of strong signals being received suddenly getting
> loud.
There's not ever been a receiver that could receive signals with AGC
without the user riding the RF gain control. Leaky AGC capacitors can
often contribute to almost good AGC operation where the last IF stages
and the product detector just clip a little.
>
> But I'm also wondering if it's old, leaky caps. After restoring the
> audio mod as we discussed, my plan is to work backwards in the audio
> chain, replacing electrolytic caps as I go.
>
> Rick, KR9D
>
73, Jerry, K0CQ
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