[volt-nuts] LM3900

[Charles Steinmetz]

Attila wrote:

> Theoretically yes, in practice you are better off using an opamp
> that is not 40 years old and not as quirky as a Norton opamp.

They are also perhaps the noisiest op-amps ever marketed.  They invite 
one to add the missing PNP differential input pair externally, but even 
this is very disappointing due to the extremely low internal currents in 
the 3900.  Of course, this also makes them very slow.

There is one semi-clever trick 3900s will play -- with one section and 
no diodes, you can make a half-wave rectifier, and with three sections 
and no diodes, you can make a full-wave rectifier (the Tracor 900A uses 
them this way).  But again, extremely, miserably, intolerably noisy.

Best regards,

Charles