In the "Replacement for 741" thread, this came up, which seems like it deserves its own thread.
One glaring exception that I'm having my face rubbed in at the moment is the surpassing excellence of the late lamented LF357. It has very very low input capacitance, lowish noise for 1976 or whenever it came out, and 20 MHz of bandwidth.
None of the >30V op amps I've tried has been able to touch it as a low-level TIA for use with a bootstrapped PD and common-base stage, which is one of the examples from my Front Ends chapter (the very last thing to wrap up before shipping the book off).
The circuit uses a 301k // 0.4 pF feedback network with a BFU520A common-base stage and an MPSA18 bootstrap. (There are MPSA18 equivalents that you can still get.) The problem is the Johnson noise of the 301k resistor, differentiated by the op amp's input capacitance.
It works beautifully with LF357s from my stash, but fails miserably with: OPA140, OPA172, OPA604A, TLE2081, LT1122,
all of which ought to have worked if their datasheet Cin specs bore any relation to reality. (Spoiler: they don't.)
Friday I'll try it with reduced supply voltage and an ADA4817-1. It really frosts my shorts to give away 10 dB of dynamic range (+-5 vs
+-15), even while paying 10x more for the amplifier.I'll update this when I have more data. In the mean time,
Got any more examples of (electronic) stuff you used to do but can't anymore on account of obsolete parts? You can (sort of) get 5 GHz PNPs again, so that one is (sort of) fixed, but there must be lots of others.
Cheers
Phil Hobbs