[sdiy] Op-amps CA3140 v. TL074

[David G. Dixon]

> Agreed - with that high input impedance, the CA3140 is an unbeatable
> buffer for sample and hold, or integrators for filter stages and
> oscillators.
> They work great off of single-ended 5V power supplies - the output can
> swing all the way down to the negative rail. Handy for analog<->logic
> interfacing.
> The CA3140 has a special niche that it does very well - no surprise they
> are still in production.
> The only "gotchas" are ESD sensitivity*, and the fact that the output
> can only source 10mA and sink 1mA.
> *I think I've killed maybe 10 CA3140s in the past 30 years.

For CV buffers (S&H, etc), I typically use the LF44n (esp. the LF444, which
is a relatively low-cost quad).  These are JFET input opamps with 10^12 ohm
input impedance (compared to about 1.5 x 10^12 ohm for CA3140) and 50pA bias
current (compared to 10pA for CA3140).  They are insensitive to static
discharge.  However, they suffer from a low slew rate (only about 1V/us,
compared to 9V/us for CA3140), which is why they are probably only suitable
for CV buffering.