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wrenchone 19th August 2010 06:16 AM

Polystyrene Caps For Filters
 
I'm putting together some upgraded version of some RIAA amps and active crossover circuits. I have the choice of several caps for filter duty, including the green Russian polystyrene caps available on Ebay, some Rifa PFE225 radial polystyrenes, some Mallory radial polystyrenes that are a Rifa PFE225 look-alike (same style case, red instead of white), and as an alternative, Roederstein MKP1830 and 1840 series polypropylene caps. These would be used in RIAA passive and jfet follower-based Sallen-Key active filters.

Does anyone have any useful experience with these caps? I suspect they're all pretty decent, but are some more decent than others?

Joachim Gerhard 19th August 2010 06:24 AM

I would prefer the Roederstein. They sound very transparent and neutral. One of my favourits after 30 years of listening. Very thought after in Japan and Germany.

qusp 29th August 2010 02:24 PM

yeah go the roedestein or if you can find the rifa polypropylene they are very nice also

jacco vermeulen 30th August 2010 11:47 AM

1 Attachment(s)
Obviously, the Roederstein MKP1840 is the only of the lot for higher uF values, but Metallised foil.
The Metal Foil KP1830 (1837) is the choice for lower values, if a high voltage rating is required.

For RIAA and X-over, my preference goes to Polystyrene caps, provided they're the extended foil kind.
The box-type Polystyrene cap in general is the variety with interleaved foils, the RiFa PFE225 has the disadvantage of fairly large size and 2% accuracy.
Others came in 1% grade, such as the filthy expensive Siemens KS, all just as easy to solder as a KP1830, due to the thick leads and large epoxy resin mass.
Example of ITT KS (= Kunststoff Styroflex) caps :
Wieder mal 'ne Kondensatorfrage - Phono - Restauration und Selbstbau - Analog-Forum
Others : http://www.analog-forum.de/wbboard/i...786&type=image

Never seen/heard of radial Mallory polystyrenes, a picture would be grand.

jameshillj 30th August 2010 02:59 PM

Rifa pfe225
 
I would suggest you avoid the Rifa pfe225 extended foil caps - unfortunately, they're not particularly good - originally intended for the vocal range in phone systems.
Now the Rifa pfe216 styrenes, they are very good, but also physically large, and there is a limited range of these NOS caps at "Rockby Electronics" in Oz.

wrenchone 30th August 2010 06:40 PM

In the active crossover I'm currently building, I went with Roederstein KP1830 caps (1n5, 100V). They're very compact, and the value is pretty much perfect for a crossover fequency range of 5-6 kHz. I used the Russian K71-7 series polystyrenes (100nF, 250V) for input coupling and high-pass output coupling, and some Aerovox AFPS series polypropylenes (3uF, 450V) for loww-pass output coupling. The Aerovox caps reportedly sound pretty good, in spite of their humble origins.

jacco vermeulen 30th August 2010 07:32 PM

Quote:

Originally Posted by wrenchone (Post 2288360)
Aerovox AFPS

Why humble, there's nothing wrong with the Mexi-Cans.

http://www.youtube.com/watch?v=gQU02n358VY

wrenchone 30th August 2010 08:05 PM

Maybe so, Jacco, but Tecate capacitors are another thing altogether - stay away....

wrenchone 31st August 2010 04:13 AM

I have a whole mess of odd polystyrene and polypropylene caps acquired over the years. Sadly, the only Siemens caps I've seen are the usual metalized polyesters (and a stacked foil or two). I've been collecting a fair number of Arcotronics, Rifa, and GE HV, high current metallized polypropylenes for coupling duty in tube amps. I have a sprinking of old-style Rifa polystyrene caps, including some PFE210 caps that are very obviously extended foil units, as they are encapsulated in clear resin so you can see exactly what's going on at the end terminations.

oncle_tom 31st August 2010 10:48 AM

Hi Jacco,

what do you prefer for bypassing? KP or KS? I have both types from Siemens at hand but i'm not sure what to take from the technical view.

Peter


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