Re: gEDA-user: ideal op amps in gschem

[Al Davis <ad82@xxxxxxxxxxxxxxxx>]

On Wednesday 25 January 2006 17:03, Dan McMahill wrote:
> > This is a little circuit with only an op-amp and 3
> > passives.  Can't get more simple than that right?  Turns
> > out that the designers of it had some troubles
> > understanding it.
> >
> > The answers (to an accurate enough degree for engineering
> > calculations) can be had in about 3 lines of hand analysis
> > but I think it illustrates nicely how one must be careful
> > with those "ideal" op-amps.  It's also a good case of where
> > one shouldn't substitute a simulator (with a model which
> > may not capture important details) for thinking!
> >
> > Have fun.
> >
> > -Dan
> >
> >
> > p.s.  hint:  The pin on the schematic is the only
> > connection (other than power and ground) to the rest of the
> > circuit that this little gem was found in.
>
> In case anyone wants a bigger hint, here is the context in
> which that op-amp circuit was found.

Here's another hint.  This link is to a product that I designed 
that actually uses that circuit (with different component 
values), 10 times.

http://www.apiaudio.com/560.html
http://www.primalgear.com/apieq02.html

Google for "API 560 equalizer" to find out more.

One error in API's own data sheet  ...  It wasn't first released 
in 1969.  The real date was 1976 or 1977.