David, > So now, TL064 is my standard opamp for those buffers. Maybe one of these days I'll look for a relatively inexpensive quad with really low IBC (1 pA or less) -- anybody have any suggestions? If you can cope with single-supply op-amps then the TLC272 series is pretty good, with Ibc(typ) around 0.7pA. Neil -- http://www.njohnson.co.uk