[sdiy] S&H

[Tom May]

I built an S&H using the LF398 and I remember at the time thinking I
would never do it again, since it didn't seem the LF398 was really
buying much over using a discrete circuit.  Mine took a few more parts
because I needed a one-shot to create the correct pulse from an edge.
I even put in a trimmable hold step compensator that works well.  But
what I didn't like was that at some point I decided I wanted to try
the Electronotes variation of putting in a slew rate limiting resistor
somewhere so that a sample pulse would not cause the output to go all
the way to the input, but only an adjustable fraction of the way.  The
terminals necessary to do this aren't brought out to pins.  For me,
the lack of flexibility didn't make up for the slightly smaller parts
count.  I eventually figured out a way to simulate the EN trick, but
it's rather imperfect.  I'm not sure I can find a circuit diagram for
that board any more . . .

Tom.

Peter Grenader <petergrenader at mksound.com> writes:

> Kids,
> 
> I've just built a honey of a S+H using National's LF398.  You hang a tranny
> and a very small compliment of res's, caps - and bang - seems to work just
> fine.  Mine has an option of either a stepped output or a smoothed out,
> which takes the first and runs it through a 1 meg pot-controlled RC to a
> 50uf cap nto op amp lag circuit.
> 
> works great.
> 
> Not very sophisticated, but i was in need one just one more sampling device
> and this was painless and hums along like a bee.
> 
> Peter