This thread may have something helpful?

https://forum.allaboutcircuits.com/threads/which-op-amps-do-you-use.142355/#post-1202567

 

So I was Googling high input resistance OP Amps and ran across a LM11 which rang a bell in my memory--sure enough, I have a couple in my asst. So I'll try that a while and if it comes closer then I'll get the one you mentioned. Thanks again. By the way, "Try again" in my time line is sometimes a week, sometimes only a day.

 

When browsing Digikey you are using the filters for the product suggestions
displayed in Excel ? That will cut down a lot.

Regards, Dana.

 

For some useful information, check the December edition of "analog dialog", an on-line publication of Analog Devices company. It has two discussions about instrument amplifiers. And one of those devices has the specs that your application can use.

 

@ebp OH YES! I put a op amp between my 10k pot and the input of a second voltage follower made from a LM11C which I happened to have. This is claimed to have low input Offset Voltage and Input Bias.

Everything worked smoothly. Then I put a 70 megohm resistor (don't ask--just an impulse buy some months ago) in between the output of the first op amp and the input of the second. And I got a drop from 3.4066 volts to 3.4058 volts. I can't even contemplate what the actual input resistance is, but it is plenty for my purposes!

I'm going to put the circuit on a board and proceed. I wouldn't be here if it were not for you and others offering guidance and encouragement to an old man whose last electronic experience was with KT88s and 12AX7s.

 

@ebp OH YES! I put a op amp between my 10k pot and the input of a second voltage follower made from a LM11C which I happened to have. This is claimed to have low input Offset Voltage and Input Bias.

Everything worked smoothly. Then I put a 70 megohm resistor (don't ask--just an impulse buy some months ago) in between the output of the first op amp and the input of the second. And I got a drop from 3.4066 volts to 3.4058 volts. I can't even contemplate what the actual input resistance is, but it is plenty for my purposes!

I'm going to put the circuit on a board and proceed. I wouldn't be here if it were not for you and others offering guidance and encouragement to an old man whose last electronic experience was with KT88s and 12AX7s.

At those obviously "high" impedance levels you need to be aware of leakage paths and materials that act like capacitors having charges stored that lead to confusion. Bob Pease wrote a number of very educational documents about the effects, if you can find copies of his publications the education is worth the effort, big time.

 

Here is Bob Pease collection of articles, in particular go to page 4, a list of articles,
several on HiZ low bias.....-

https://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf


Regards, Dana.

 

Here is Bob Pease collection of articles, in particular go to page 4, a list of articles,
several on HiZ low bias.....-

https://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf


Regards, Dana.

Thank You ever so much Danadak. Bob Pease was a master, no doubt. His insights and understandings were a valuable asset to many of us, including me. AND his explanations are far better than what I can say.