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BAV199 are suitable for mike preamps like THAT 1512 but are too noisy for condensor mike stuff.? You want something like Ir 0.2pA.? There's nothing spec'd to that level as its very temp. dependent.? You just have to guess that the paper spec. is pessimistic and by experience.

OK, so I accept it is impracticable on a condenser mic - the broader question for me is? - What is the upper limit of input impedance where a diode ESD protection scheme can work effectively with low noise? And which diode is best suited to that?

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BTW, the THAT datasheets recommend 1n4004GP.? There's some AES papers on The Phantom Menace by THAT & Wayne Kirkwood that explains the choice.

do you mean this one?

From a brief look it seems it explains the protection circuit, but I couldn't see anything about why they chose 1N4004GP specifically. Unless it is implicit in some way I didn't understand.

They also seem to be mostly concerned about the sorts of faults caused by plugging in live phantom powered cables to a low Z mic input, which is quite a different situation from ESD on an exposed HiZ input.

A mic preamp input is concerned with noise because it has high gain following it, wheras my buffer circuit is unity gain or less and concerned with noise in quite a different way.?

I'm at least as concerned about diode leakage throwing off the fet bias as I am about noise. Though the solution may be the same.

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I don't think diodes with leakage low enough not to introduce noise to a 1G input will protect anything.? They? will be too fragile and too low Vr Reverse Voltage.? They are suitable to run FETs at Idss for something like simpleP48.

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That's not to say they don't exist cos some must be integrated in OPAs

yes, as above, I'm wondering where the practical upper impedance limit is.

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