>
> As Dave has stated , it appears that the
> thumper is inherant with the 4066. I started re-thinking the
> whole problem.
>
I don't have a 38s so I may be speaking out of turn here.
That said, I doubt that the 4066 is the problem. I have used
the 4066 in numerous low level applications for more years
that I care to admit and find it to be an excellent switch. I'll
bet the problem is elsewhere.
If the sidetone is being generated by logic circuits, I think you
will find that the thump is coming from the DC shift that occurs
as the sidetone is being turned on and off.
Consider this. When the sidetone is off, the output of the sidetone
generator is zero (or Vcc). When the sidetone generator is turned
on, it is switching between zero and Vcc at an audio rate. If the
duty cycle is 50%, the average output is 1/2 Vcc. The shift from
zero to 1/2 Vcc back to zero when the sidetone is turned on and
off, has a time constant that is determined by circuit constants and
which is likely to make the DC shift audible as a thump.
There are ways to eliminate this shift by careful design.
-Lee-
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