SV: Re: [sdiy] LF357 as follower / departure from ideal opamp behaviour

[Pat Kammerer]

> > > > > You've got it backwards!  The 3140 is super high input impedance
and
> >*the*
> > > > > one to use for the buffer.  I've compared good JFET opamps for
buffers
> >and
> > > > > the 3140 is better.
> > > > >
> > > >
> > > >You may be right, but my design works pretty good.  : )  I really am
just
> > > >now starting to get my head around op amps.  I'm no expert.
> > >
> > > I'm sure it works "pretty good".  But try looking at the droop rate
with
> > > the opamps reversed and I'm pretty sure you will see a big difference.
:-)
> > >
> >
> >I'm not sure what you mean, "op amps reversed"? The AD781 is not really
an
> >op amp, but a monolithic SHA.  The 3140 is only external circuitry such
as
> >trigger extractor and slew generator.
>
> OK, I'm totally lost.  PS said use the AD82x opamp for the S/H buffer, and
> I thought you agreed, no?  Guess I totally misunderstood.  Sorry.
>

I could be wrong though, I though someone mentioned AD781.  It could very
well be my misunderstanding or a typo.  Quite sorry.  I knew the
conversation was slipping away from things that made sense.  : )