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Old 5th June 2008, 05:56 PM   #1
rtate is offline rtate  Canada
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Default Film Capacitor materials

I would like to know the "pecking" order for materials used in film capacitors for audio.
So generally speaking would polypropelyne be better than polyester? as well as metalized compared to non metalized?.
Where do foil and film/foil combinations fit in? Are they better?
I always thought that polystryene was at the top end for materials but now I'm not so sure!!

I know this is a very subjective question, but I read that the "wima" brand is not well regarded in audio so is there a couple of brands that are beter to use in solid state amplifers.
I have used Wima's in the past but have nothing to compare them against.
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Old 5th June 2008, 06:53 PM   #2
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rtate,
here it is especially for you, in order of decreasing audio quality and operating frequency range, increasing dielectric and resistive losses and coloration:
1 Polytetrafluorethylene (PTFE, teflon)
2 Polystyrene (styrene, styroflex, styrol)
3 Polypropylene
4 Polycarbonate
5 Polyester (Mylar)
Non-metalized film is better than metalized film, higher voltage rating and larger physical size as well.
Wima capacitors do have very high sonic and technical quality.
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Old 5th June 2008, 07:05 PM   #3
SY is offline SY  United States
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Wimas are excellent, in my experience. Many of the so-called better caps perform worse (especially with regard to microphonics), and none can be shown to perform significantly better in an audio application.
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Old 5th June 2008, 07:09 PM   #4
lineup is offline lineup  Sweden
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Default Re: Film Capacitor materials

Quote:
Originally posted by rtate
I would like to know the "pecking" order for materials used in film capacitors for audio.

- So generally speaking would polypropelyne be better than polyester?

- as well as metalized compared to non metalized?.
To Both questions: Yes!

Sometimes is not easy to know if a polester / polypropylene is metallized.

The ranking goes:

0. No cap at all. DC in - DC out ..... uses this!

1. Polystyrene (very hard to find, and only values in pF range)

2. Polypropylene. A bit more expesive than MKT, metallized Polyester

2b. Polycabonate. Good, but seems not made any more.

3. Metallized Polyester. MKT. Among others Philips has made
lightblue coloured squared of these.

These above are Audio quality for signal coupling.
What we should go for.
-------
4. Polyester. Good for op amp power supply pin bypassing. Usually 100nF.
And other use in amplifiers, where not directly signal travels.

--------------------
If you search forum., you will find plenty of good topics about Audio Quality capacitors.

The most often quoted investigation work and classical paper
is by Jung / March
This is a very good work, with tests of all sorts of caps
and a compare and conclusion how we could best use different material capacitors in Audio.
And how NOT to do
Quote:
PICKING CAPACITORS

Walter G. Jung and Richard Marsh
Reprinted from Audio Magazine, February and March, 1980
Directly form Walt Jung website, http://waltjung.org/
http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
http://waltjung.org/PDFs/Picking_Capacitors_2.pdf
http://waltjung.org/PDFs/A_RealTime_...or_Quality.pdf

.
There are some new 'exotic' caps. Very expensive and often not easy to find everywhere in our big world.
Materials like teflon and some sulfide something.

Lineup audio cap regars
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Old 5th June 2008, 09:59 PM   #5
rtate is offline rtate  Canada
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Thanks for the replys they are very helpful!!

So where does "silvermica" fit in this pecking order?
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Old 5th June 2008, 10:01 PM   #6
SY is offline SY  United States
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Very high dielectric absorption. Ideal for RF bypass.
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Old 5th June 2008, 10:04 PM   #7
rtate is offline rtate  Canada
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But are they better than say.... polyester?
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Old 6th June 2008, 03:35 PM   #8
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rtate,
you should stick with film capacitors.
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Old 6th June 2008, 05:11 PM   #9
SY is offline SY  United States
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Quote:
Originally posted by rtate
But are they better than say.... polyester?
For what? Each cap type exists for a reason and different circuit functions have different needs.
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Old 6th June 2008, 05:26 PM   #10
jcx is offline jcx  United States
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THE BEST OF BOB PEASE
Understand Capacitor Soakage to Optimize Analog Systems:

http://www.national.com/rap/Applicat...570,28,00.html


plots DA for some cap dielectric types, the usual assumption is that DA is a good proxy for "audio quality" (although much searching hasn't shown me a theoretical justification)

but assuming that DA ~= audio quality then silver mica are in the same range as polyester - depending on material details mylar can be "better" according to Bob's graph

also Bob's graph suggests NP0/C0G ceramic should be a superior substitute for silver mica with similar high (at least for audio amplifiers) frequency properties as well
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