[sdiy] low input bias current opamps

David G Dixon dixon at mail.ubc.ca
Wed Aug 15 19:37:24 CEST 2018

Thanks for the great response, Roman.
Possibly stupid follow-up question:  
Why would ESD have an effect on a JFET-input opamp?  I thought that only
CMOS was susceptible to ESD, because of the oxide gate insulator, but not
JFET.  The LF444 should be no more susceptible to handling issues than
TL074.  The handling would have to have been unbelievably abusive to damage
the chips, I would have thought.
If I'm wrong about this, please disabuse me!


From: Roman [mailto:modular at go2.pl] 
Sent: Wednesday, August 15, 2018 9:10 AM
To: David G Dixon; synth-diy at synth-diy.org
Subject: Odp: [sdiy] low input bias current opamps

The answer to A) is no, because of 1)

Recently I made some THT design and was just so happy about it until I found
how many parts that I freely use in SMD are simply not made in THT, so the
choice usually comes to one part if any.

The answer to B) is usually Mouser, but they have sometimes errors in
describing parameters, or take different values to the table, like "typical"
for one part and "minimum" for the other part. Sometimes I use DigiKey,
mostly because they seem to have more refined parameters to search and I can
type the quantity of interest, and then sort by the price. Mouser sorts only
at qty 1 which is useless.

And obviously all manufacturer's websites contain parametric search, which
is the most accuratre, but still I prefer Mouser because it gives me
guidance of the price and availability.

And if it's for some S&H, why don't you stick with TL0xx? Are you sure your
switching key has lower leakage than bias of TL0xx opamp? Or try LF347 maybe
but it's inferior to LF444 in this application anyway.

Give LF444 a chance, get new ones, maybe they were handled very badly and
inputs were damaged by ESD because of bad storage. They would still work but
bias may be in range of nA instead of pA.


Dnia 15 sierpnia 2018 05:48 David G Dixon <dixon at mail.ubc.ca> napisał(a):

Hey Team,

I'm looking for opamps with the following properties:

1) Through-hole

2) Quad opamp

3) 14-DIP package

4) High power range (+/-18V, say)

5) Low input bias current (10 pA or less typical)

6) Pin-compatible with TL074, etc.

7) Not LF444 (cuz they all seem to be defective)

So, basically, I'm looking for a suitable alternative for LF444.

So, here are my questions:

A) Do you know of such a thing

B) How does one go about finding such a thing, generally?

Thanks in advance!

Dave (Floating VCA) Dixon


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