i feel kind of dumb , because i forget about ac+dc voltages at all :] oh well.
I was browsing TME site for avalable rms-dc converters and i find another one i might be interested
while ltc1968 have pretty good performance and bandwitch, not to mention pretty simple aplication. It look more like a dedicated part for being build into a multimeter, besides the shop have a really small quantiti of those, under 10 pieces
so i did a search for rms-dc converters and AD736JNZ poped up
AD736JNZ, they have more tnan 700 of those and the price is also a bit smaller.
It have smaller bandwidth , but still enough i thinh, can be powered from 16,5V+- and accept input voltages up to 12V+- p-p (1Vrms for power suply 5 to 16V+-) so it would work great from two 9v batteries as a stand alone unit , there is even a bunch of different aplications to use it , like for example adustable gain of the output voltage and premade input voltage devider. Not to mention it is in dip package so it wuld be easier to not destroy while soldering :] Not if i would destroy an smd package.
with input devider of 10 i would have 500-800mVrms at 3,5V p-p so i think a pretty resonable parameters for this converter