My 3rd 3458A is not golden, so need to goldify it myself.
Main goal to get <0.2 uVpk-pk noise, so I can avoid need of external 10V reference for calibrations.
what if you lower the temperature of the entire 3458a? then maybe have a LTZ heater at 30C?
https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/450/dont know what is the set point of jorns LTZ, maybe 65C ?
that post, jorns stdev = 0.37uV @ 18C, is this better than most DMM/LTZ?
and its a 34470a
maybe a cooler LTZ with smaller R1 ... 10mA ? but looking at some other posts, it seems to indicate that the noise of LTZ is not smallest at higher current. i cannot remember the post, after 3mA, noise increases?
did you try your select LTZ at different R1 and see if each has a low noise at a different current? I am wondering if each LTZ noise is exactly the same at exact same current, which i think is not true. that could mean sort by noise instead of Vz? but i dont know ... never build one of these before ...
i always have a thinking that stability can be mitigated by removing temperature problems (that is after reading all the wonderful tempco experiments of cos)
but noise? can noise be mitigated by tweaking temperature as well?
kill the mad cow tempco, murder the humidity, now .... what do we do with the noise ...
i did see some articles about cooling to reduce 1/f noise ... but i dont know. im sure its not the LN type of cooling, i think electronics are not specially made for LN. esp when there is humidity around