NPO ceramic vs polypropylene
There was a little side discussion on JL?s LC tuning thread. When I look ed at this ~2 years ago I found that ceramics were a tad better than the ?good? poly-pro?s. (I used them in a low freq LCR circuit.. Q~35 so the cap type didn?t make that much of a difference.) (The poly pro?s I have are from Panasonic. low dissipation 2% caps. I can dig up a part number if it?s important, I?m not sure they are made anymore.) So these are both 10nF caps. I first measured them on an SRS720. at 10 and 100kHz.
10kHz 100kHz type C R D R D NPO 10.17 0.6 0.0004 0.006 0.00003 poly 10.16 0.23 0.00013 0.086 0.0056The R/D numbers are so low I don?t really believe them. So I stuck the C?s in the (original) LCR circuit. So I list peak frequen cy, Vin and Vout. (As measured on a ?scope (digital w/average))
type freq. Vin Vout NPO 6.08kHz 159mV 6.40V poly 6.13kHz 159mV 6.36V
(again no real difference to talk about.) I pulled out a different L...
type freq. Vin Vout NPO 157kHz 91.2mV 7.36V poly 158.5kHz 92.8mV 7.24V
Finally a bit of difference I can believe. Vin dropped because the series L C was loading down the function gen.
So for those who think film are better, you might want to look again at NPO ceramics. They've improved a lot*. Of course this says nothing about the DA of the caps. (How does one go about measuring that?) George H.
*you need to get the new little ones.. the old larger npo ceramics with the dull brown coating are not nearly as good.