[sdiy] Happenin' new opamp

[David G Dixon]

Hey Oren,
 
The typical IBC for CA3140 is 10pA, which is the same as LF444 (presuming
they actually work).  LF444 is cheap as chips and is a "standard pinout"
quad.  Hence, I'd stick with it (presuming I could actually get some that
weren't garbage).
 
The CA3130 is twice as good, with typical IBC of 5 pA.  However, again, it
is only a single opamp.  I need a quad (I'm not going to completely redo the
layout).
 
Any good quads (better than LF444)?
 
  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Oren
Leavitt
Sent: Thursday, April 26, 2018 10:02 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Happenin' new opamp



Not bad! I happen to have a few tubes of TL06x sitting around - a use for
'em!

CA3140/3130 are still today some of the best for S&H circuits with just a
few pA of input current


- Oren



On 4/26/18 11:42 AM, David G Dixon wrote:


Agreed, and agreed.
 
I have made a (somewhat well known) version of the CGS analog shift register
for quite a few people, with a number of improvements over the original.  I
had traditionally used LF444 for the S&H buffers because of its low input
bias current (typically 10 pA).  However, recently, I bought a number of
them from a local shop (they had been sourced from Digikey), and they turned
out to be defective (or counterfeit -- I'm not sure, they just don't work).
Out of desperation, I ended up using a TL064 instead (typical IBC 30 pA,
compared to 65 pA for TL074) because that was the next best thing I had in
my stores, and it worked like a dream.  Very little S&H drift, even in
"loop" mode (where the same three stored voltages are looped around the ASR
outputs over and over).  I use 0.1uF caps in these S&H circuits, so 30 pA
generates very little drift (about 300 uV/s, which I guess I can live with).
 
So now, TL064 is my standard opamp for those buffers.  Maybe one of these
days I'll look for a relatively inexpensive quad with really low IBC (1 pA
or less) -- anybody have any suggestions?
 
 
  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
Mattias Rickardsson
Sent: Thursday, April 26, 2018 2:54 AM
To: Michael E Caloroso
Cc: SDIY List
Subject: Re: [sdiy] Happenin' new opamp



On 25 April 2018 at 06:15, Michael E Caloroso <mec.forumreader at gmail.com>
wrote:


The input offsets - hence CV error and drift - are temperature
dependent.  A substrate quad is going to generate more heat than a
single or dual.

There's a reason you see single opamps on the input stages of VCOs.



Ah, thanks for pointing that out.

Speaking of CV and favourite op-amps, I prefer using TL064 for CV
multiplexing. They are quad, but low-power - so they keep cool.

When I come to think of it... I also very much prefer quads due to them
having the outputs on the corner pins. Very easy to probe and measure on.
It's a pity that the dual op-amps got the pinout they got, with an output on
pin 7. :-)

/mr



 

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