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For an opamp input, which network protection is preferable?
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schmitt trigger:
Wow!!
Excellent advice Tim. I find the idea of bootstrapping the ESD diodes very clever.

For the 10k input resistor, I had already considered using multiple devices in series, both to increase power rating and the voltage withstanding capabilities.

As I mentioned in my original post, the purpose of this little circuit is to extend the low level range, and increase the input impedance of an analog meter (full scale = 2.5 volts AC, 9kohm/volt).
As such I don't require terribly high accuracy (0.5% would be excellent) nor ultra-high impedance (although 1 Meg would be nice to achieve).
The meter is reasonably accurate to 100 Khz, so I would also like that bandwidth, too.

Initially, I had wanted the amp to also be useful at DC, but if the offset proves to be a chore, I can always AC couple the output.
iMo:
Do you need the diodes actually? With 100k input resistor and say 5mA opapm's clamping diodes max current the input voltage could be around 1000Vpp.
schmitt trigger:
As I mentioned to Marco, I wasn't seeing the forest because I was focused on a tree.

But this discussion so far has been very enlightening, and I've learned a pair of new tricks which I wasn't aware before.
Kalvin:
LEDs and diodes will produce some current (read:offset voltage into op amps inputs) when exposed to light, so use a good enclosure which will block light 100%.
magic:

--- Quote from: schmitt trigger on April 18, 2019, 12:29:53 am ---I cannot have low voltage offset AND at least 1Meg input impedance AND overload protection AND wide bandwidth.

--- End quote ---
Perhaps some of TI's e-trim opamps? Picoamps of input current, okay input capacitance for a FET, microvolts of offset and offset thermal drift, reasonable noise, good CMRR up to 3V below VCC or so, rated for ±10mA input overload, a few MHz of GBW, not terribly expensive too. OPA191, OPA192, OPA376 are types I know.
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