http://elecraft.85.s1.nabble.com/KX1-speaker-output-with-superimposed-oscillation-tp452289p452291.html
Thanks for posting the solution to this problem. I feel sure there are
a number of us who read about it with interest but did not comment.
> Hi Bob,
>
> Finally, I got it !.
> It is related with "the RC network connected between the output pin 5
> and ground, required to keep the amplifier stable at high frequencies
> at different loads", as you mention on your previous post.
> I checked the RC network and I even installed a new one: same behavior.
> If I removed this RC network completely, the oscillation now started
> with lower volumes !.
>
> Using the technique "try and error", the problem was solved with a
> capacitor of 68 nF in parallel with this RC network, that is, just
> from pin 5 to ground. No more high frequency oscillation with
> different loads !.
>
> By the way, the DC voltage at pin 5 was half the supply: 3 V. I even
> installed a short leads 10 uF tantalum across the supply of U4,
> without positive results.
>
> I don't know the reason of this behaviour, maybe, as you say on your
> post, is due to the high gain of this stage (46 dB). Who knows... .
>
> Many thanks Bob and have a good day.
>
> 73,
> Paco
>
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