[sdiy] low input bias current opamps

David Manley dlmanley at sonic.net
Wed Aug 15 10:58:22 CEST 2018


On 8/15/18 1:31 AM, David G Dixon wrote:
> Yes, that one looks good, and is less than half the cost of OPA404.  I'm
> tempted...
>
> The thing about LF444 is that I bought a bunch of them from a local shop who
> had bought them from Digikey, and none of them worked.  When I put them in
> my ASR circuit, they drifted, like portamento, many mV per second.  I'm one
> of those "once bitten, twice shy" sorta guys, so I'm very hesitant to buy
> them again.
>
> I should probably just buy a few from Digikey and assume that they'll be OK,
> but if they aren't, I may actually burst into flames from rage.  So, that's
> a risk.
>
A few questions:

1. are you using the typical guard ring circuit around the high 
impedance node on the hold cap?

2. is your board clean of any impurities that might allow leakage from 
there?

3. what are you using for an analog switch?


-Dave





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