i see, i dont quite understand the calculation, how does 1 do the conversion from PDF spec nV/sqrt(Hz) to compare the SDV? if 10NPLC approximates to 100nV/sqrt(hz), how do we translate robrenz's tek4050 (
73nV SDV)?
i think i caught a glimpse of his SDV in the LTZ1000 or was it the LM399 discussion thread. found it (
https://www.eevblog.com/forum/testgear/tektronix-dmm-4050-shows-exceptionally-good-performance/msg388153/#msg388153), is the lower noise record due to 100NPLC?
since a few hours have gone by, there is some logs in the bag. originally the intent of the mini fan inside was to circulate air and reduce some temperature, but now as i have converted fully to TO-92 BJT, i thought i log some w/o fan working. and it came out even better. no pops and sizzles ! yum yum !
i will just copy the XLS result as is, the numbers are arranged as follows
AVERAGE | | STDEV (in nV) all plots are 100mV scale 10NPLC, AZERO on. manual REL +2uV
SKEW | | AVEDEV
KURT | | TRIMMEAN
plot 0204
-324.7052777778 526.0146096479
-0.1100208528 525.8307811728
-0.799885848 1.0006576714
plot 0304
-1470.1225 157.6810638436
0.1302137461 125.8797902778
0.178574312 1.0009115936
plot 0404
-1402.9163888889 179.471967593
0.1201923798 158.0596367284
-0.2535748744 1.0012086594
plot 0504
-1141.2641666667 153.2140025044
0.005902222 123.2643449074
0.2425810864 1.0002417992
plot 0604
-1085.2594444445 153.3506986219
0.0867791975 122.6290722222
-0.0720036643 1.0008171796
plot 0704
-1128.9155555556 155.5941890996
0.0283555016 123.0794123457
-0.0130345579 1.0000723408
*edit : i should also add that the FLIR-ed temperature of the BC5xx BJT is approx 41oC. that is way way under the 61-65oC of the SOT23 BJT packages. i also need to mention that the bootstrapped current regulator resistor has been modded also to a higher value of 172ohms from 150ohms, a reduction of approx 0.5mA final PCB air temperature 43.2
oC, trafo temp 42.8
oC
hmmm another 50nV to shave off perhaps
... well this is getting exciting
(come to think of it, all along i had the wrong impression that the noise came from my dirty AC mains, and i have not added the large 100mH filter yet)