Attila Kinali

On Wed, 2 Nov 2016 15:11:24 +0100, you wrote: >On Wed, 02 Nov 2016 08:44:18 -0500 >David <davidwhess@gmail.com> wrote: > >> Charles pretty much covered it but I am not sure that polypropylene is >> always worse than polystyrene. Some of the other plastic films are >> pretty good also but polypropylene is the most common high performance >> option. Teflon is the best but is also expensive and has poor >> availablity. > >Polyphenyle sulfide (PPS) seems to be the new kid on the block >with quite good performance values (dielectric absorbtion, moisture >and temperature dependence) and quite readily available. > >As with all film capacitors: be carefull and quick when handsoldering. > > Attila Kinali I don't know; the datasheets I checked for PPS capacitors did not list dielectric absorption other than "low", which is always worrying, and specified 1/2 to 1/3rd the insulation resistance of polypropylene. In practice practically nobody is going to specify capacitors for applications like this so the only way to really know is to test and grade them yourself. This is what I have always ended up doing in the past; the datasheets were just a starting point for finding suitable candidates.

The Russian K72P teflon capacitors on ebay are really good and not expensive. They are however, huge! I was investigating replacing the integration capacitor in an HP 3455A (it is responsible for the +/- 2 digit jitter in auto-cal mode). I have now replaced the original polypro 82nF with two K72P 39nF in parallel and the reduce the jitter to less than one digit. Unfortunately, physically, the K72Ps don't fit and dangle over the edge of the AtoD board. The 82nF K72P I tried was worse! I built Bob Pease's dielectric absorption circuit and tested several capacitors. More details here: http://www.eevblog.com/forum/testgear/hp-3455a-last-digit-jitter-in-hi-res-auto-cal-mode/ There are a couple of oscilloscope screenshots of the absorption of the original capacitor and the K72P. I've not found anything better than the original capacitor other than the K72Ps and I've tried polypro, polystyrene, C0G etc.. On Wed, Nov 2, 2016 at 7:18 AM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote: > -------- > In message <f3847ee8-a5ec-099c-91b1-d7c0b17599d4@mounty.de>, Andreas > Bergmann writes: > >On 02.11.2016 14:44, David wrote: > >> Teflon is the best but is also expensive and has poor > >> availablity. > > > >Quick check on ebay: > >http://www.ebay.com/bhp/teflon-capacitor > > > >One pair for $150.-? wohooo .... > >Is this a part of the audiophoolery community? > > Yes, they are very much in demand for audiohomoepathy, up to the > point where people actually roll their own. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. >