Noise in tantalum SMT caps?

[John Devereux]

Have you tried C0G ceramics? You can get 0.1uF in 1206 size these
days, though a bit pricey.

Yes I did try them - they were fine IIRC. It was just the X7Rs.

When I get a chance I'll set up the (rather simple) noise spectral
density thing on the tants. Doubt I'll do any microphonics testing on
them though; it'll just be to see if they are stable under bias.

As I said, all I did was tap and flex the circuit board - any effect
should be obvious on the output of your AD797. (I have a sample of
this chip - must get round to hooking it up!)