So I finished assembly of my unit ... I made initial tests and it seems to works.
I used 120 ohm resistor instead of 100 for the first op-amp gain divider (did't find one 100 ohm in
my stock). And 100K on the second op-amp. This should give me 8K ~ of gain until I do not
replace those resistor with the correct value.
I feed a 1uV and 1mV sine wave to the amplifier at 15 Hz and it give me a 3.6K time amplification
factor that seems to me ok.
Unfortunately I cannot attach any LTZ1000 has they don't like to drive this 2mF cap and start
oscillating. The only buffered LTZ1000 don't feet inside metallic box and if I leave it outside the
box I get all sort of 50Hz crap.
I tested also with batteries and considering the 8K multiplication factor noise floor is very low ...
I will build a buffer to put between the preamp and the LTZ1000 ...
Anyway settling time is almost immediate (max 1 minute), but this was a very luky cap. I leaved
it at 7.3V for 10 days and I found it at this same voltage, leakage is almost zero.
Front:
Messy - Back:
1uV RMS - 15Hz
4AA alkaline battery noise