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Old 13th October 2012, 12:07 AM   #28151
RNMarsh is offline RNMarsh  United States
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Most caps used in speaker cross-overs are metalized film. They do not short when over-voltaged. They just burn-off met film area which over time reduces the c value. Not cool in cross-over filters. They are best used in low level signal apps.

The current capability of the ultra thin met cap is not the best for high current apps. You will get modulated esr due to temp rise. Often the C value is so large that only met caps are practical... unfortunately, the largest values are used where the current is highest -- low freq Xover- bass. I would rather parallel film and foils to get the total value required. The tweeter can usually be metalized (low current) without any side effects.

The film and foil is the more suitable choice for high current apps... like speakers and power supplies. but just be sure they are voltage rated far higher than any amp likely to be used on the speakers because they do short when over voltage causes film breakdown. But they will perform the best and stay like new sound forever in either PS or PP if made well... such as RELCAP. -Thx RNM

Last edited by RNMarsh; 13th October 2012 at 12:12 AM. Reason: Caps for high current apps -
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Old 13th October 2012, 12:24 AM   #28152
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by kgrlee View Post
But polystyrenes I've used in the past, even in packages that allow tight mounting to the PCB, show this.

The polystyrenes that the unwashed masses and Golden Pinnae brigade normally worship, are unfortunately prone to this fault.

From this, I gather that Rel Caps, if glued to your "hand carved from solid teflon by virgins" PCB, with Unobtainium epoxy (without nasty dielectric factors), will be as good as NPO/COG ceramics.

I'd still like to see some evidence that polystyrenes are better practical caps than NPO/COG ceramics.

We'll ignore trivial issues like soldering and reliability.
RELCAP is a speciality cap mfr -- makes for military and communications industries, test equipment makers etal which have to have a long life in mission critical apps and will be in the field for dozens of years without failure.
The additional requirement of higher temp soldering practices make ps caps unsuitable for many uses today. But for High End audio, use them if you can find them. yes, not all caps are created equally... you get what you pay for in that component....except in most audiophile caps sold to the unknowing.
What does practical mean? Its different for different people... but here -about High-End- I dont care about practical... just informing. -Thx RNM

Last edited by RNMarsh; 13th October 2012 at 12:32 AM.
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Old 13th October 2012, 12:50 AM   #28153
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by john curl View Post
Rel RT polystyrene caps are one of the best audio caps in the world. I use them in in the CTC Blowtorch, Vendetta Research, and Parasound products as a first preference. Ayre uses them too! They are DAMPED, and do not ring.
I found the tin foil is best and second the aluminum foil. The tin has a slightly higher esr but that helps damp transient signals. In fact, if anyone cares to know -- optimum series R for critical damping occures with a .2-.3 Ohm series resistor (.22 or .27 works fine). This value is subtracted from any other series r -- pcb/wire trace, etc. [I had a patent on this added R internally but never used it]. I also like to keep the number of dissimilar metals in the cap's joint/junction to a minimum... thus tin solder to tin foil to tin/copper leads.

There are a lot of fine points in making a superiour cap for the Highest-End products. Thx - RNM
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Old 13th October 2012, 06:18 AM   #28154
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Old 13th October 2012, 12:26 PM   #28155
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Quote:
Originally Posted by RNMarsh View Post
... For caps, there is only one mfr left that makes a superiour ps dielectric for the cap industry - they are in China. ...
BASF (Germany) still makes "Styroflex".
Styroflex® Thermoplastic Elastomer - BASF Corporation Plastics Portal
(In Europe polystyrene capacitors are quite often called "Styroflex Capacitors".) And there are still other manufacturers of polystyrene caps, you even can get them at Mouser.
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Old 13th October 2012, 12:35 PM   #28156
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Different material. Styroflex is a rubbery copolymer of styrene and an olefin, similar to Kraton or Septon. Very good for use as the rubbery part of toothbrush handles. Lousy cap material.

The best plastic resin for audio caps would be COC (or COP), but no-one is doing that yet.
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Old 13th October 2012, 12:46 PM   #28157
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Are you sure. I know you are in the branch, but ....

Styroflex (SBC) - Products - Europe - Styrolution

http://www.styrolution.net/wa/steu~e...lex/properties
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Old 13th October 2012, 01:08 PM   #28158
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"Styroflex" actually is just a trademark. In german a "Styroflex Kondensator" is a cap with polystyrol dielectric.
They look like this:
Attached Images
File Type: jpg Styroflex.jpg (26.9 KB, 180 views)
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Old 13th October 2012, 01:13 PM   #28159
SY is offline SY  United States
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Quote:
Originally Posted by PMA View Post
Yes. 100% sure. Your links confirm it- it's an SBC elastomer. That's the technical name for "thermoplastic rubber."
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Old 13th October 2012, 04:28 PM   #28160
morinix is offline morinix  United States
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RNMarsh, THANK YOU for your latest bits of capacitor wisdom.
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