Op Amp dif. CM inp. imp.

 The differential and common mode input impedance of the op amp transistor models ...

 

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[Eop]

weak input signal case study LM301 versus LF347

attempted to use the smd j-fets for the high ohmic OpAmp input but they start failing (at that) at about 80kΩ input -- top-down : each previous has some drawbacks !

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about : http://www.analog.com/en/analog-dialogue/articles/tips-on-making-fetching-discrete-amplifier.html , http://www.cordellaudio.com/JFETs/LSK489appnote.pdf

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quick 5V mod.

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[Eop]