AVR-Chat

I wonder if someone could help me with some advice please. I am trying
to use an AVR microcontroller to monitor an analogue signal. The
signal is both very low and of high impedance, so initially I wish to
experiment a little by using a general purpose amplifier between the
source and the AVR. I have found a HP 465A or a Brookdeal 9452 for not
too much cash. Does anyone have any experience with either instrument,
the HP has fixed gains of 20db or 40db while the Brookdeal is
apparently variable 30-100db so either has suitable gain.
Thanks for your time.
Doug Locke.