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

[James Patchell]

The LM301 makes a good DC amplifier (Control Voltage Summers...etc).  By 
todays standards...they are a bit clunky...but still a good opamp.

The LF357 is really meant to be a high gain, wide band amplifier... 
(phono-preamp...etc).


At 07:34 PM 2/15/2006 +0100, Karl Ekdahl wrote:
>I would guess then that using this as a s&h buffer
>would be kind of dumb since i'd need resistors to make
>a >=5 gain and that would totally suck out the current
>of the cap. So, what *are* these good for then? :)
>And while i'm at it; i've also got a bunch of LM301's
>who - to me - looks kinda crappy, any good apps for
>these??
>
>Thanks
>
>Karl
>
>--- James Patchell <patchell at cox.net> skrev:
>
> > The LF357 is a decompensated version of the
> > LF356...what this means is, the
> > minimum stable closed loop gain is about 5...with a
> > close loop gain of 1
> > (follower)...it is probably oscillating, and this is
> > what is causing the
> > apparent DC offset...
> >
> > The LF356 is the same part...but compensated for a
> > gain of 1....
> >
> > Unless of course...you are actually talking about
> > the LF347 which is a quad
> > opamp (I bring this up, since you seem to be
> > comparing the LF357 to the
> > TL074)....
> >
> >
> >
> > At 05:16 PM 2/15/2006 +0100, Karl Ekdahl wrote:
> > >Hellu, i'm doing a s&h around a LF357 since it's
> > >supposedly pretty good for this. But, a 2v input
> > >follower gives about 2.5v out which isn't nice at
> > all.
> > >I'm guessing this has to do with some non-ideal
> > >behaviour of the op.amp. but i'd like to know which
> > >parameter that's screwing it all up! Also, i'm
> > using
> > >the LF357 because of its low input bias (30pA typ).
> > I
> > >later noticed that a regular tl074 has the same
> > max.
> > >input bias as the LF357, but double the typical,
> > how
> > >much better could i "generally" expect a LF357 to
> > >be???
> > >
> > >thanks
> > >
> > >Karl
> >
> >          -Jim
> >
>***************************************************************
> > http://www.oldcrows.net/~patchell
> >
> >
>***************************************************************
> >
> >
> >

         -Jim
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http://www.oldcrows.net/~patchell

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