occam Wrote: > The Siemens (now Epcos) stacked poly caps are known for their very low > inductance, and are specifically used in ps bypass of high speed > circuity.
interesting, can you show me an actual commercial application where they are used as such? > Go to digikey, and download the PDFs, and then tell us as to their > applicability. The encapsulated Epcos polyesters are series B3252xxx > and the polypropolenes ar B3262xxx. > FWIW i'm looking at the datasheet now, and there isn't anything in it to distinguish the Epcos from other stacked film caps i've seen. in fact, there's no mention of suitability for high speed applications. that doesn't mean they aren't good caps, but i'm just not seeing what you refer to. yes, stacked types have lower inductance than wound types, but poleyester has somewhat high dielectric absorption which limits its effectiveness at high frequencies, and self-inductance is still a problem vs. a chip ceramic cap. polypropylene is out due to the large physical size which makes low self-inductance impossible, particularly since almost all PP caps are wound types. i hear there are some stacked PP types but i haven't seen them; i bet they are expensive and they are still going to be larger than their polyester equivalents. the self-inductance of film caps can lead to unpredictable resonant behavior in a high-speed circuit. engineers who have access to network analyzers and high-speed scopes know this, which is why you will almost never see film caps in a industrial/commercial high-speed digital circuit, even where cost is not a limiting factor. you might be familiar with Pete Goudreau, who coined the "Godreau Triplet" bypassing scheme which used electrolytic and ceramic caps only. i believe he based his recommendation on actual broadband impedance measurements, and he found film caps were wholly unsuitable. of course, the proof is in the listening. if you think the circuit sounds better with the film cap in, by all means leave it in. i think it would be a good idea to test both with and without it though, rather than assume the film capacitor is the right part for the job. film cap bypassing was an audiophile fad back in the 90's, and now there's a countermovement of eschewing them altogether (e.g. the gainclone minimalists). usually the correct answer is far less black and white than either faction would lead you to believe, which is why experimentation is critical. not having network analyzers or 10ghz scopes on us, we can only rely on our ears. some nerdy background info for those interested: http://www.analog.com/library/analogDialogue/Anniversary/21.html http://www.diyaudio.com/forums/showthread.php?threadid=3736 http://www.diyaudio.com/forums/showthread.php?postid=42787 -- dorkus ------------------------------------------------------------------------ dorkus's Profile: http://forums.slimdevices.com/member.php?userid=3373 View this thread: http://forums.slimdevices.com/showthread.php?t=19822 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
