[sdiy] Happenin' new opamp

[Oren Leavitt]

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 <mailto: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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