polypropylene film caps

[ConradH]

Never said you couldn't- Mylar (polyester, not ethylene) has an easily measured signature and a huge amount of anecdotal evidence that people don't like them in some locations. It's still location and circuit dependent. Some places matter, some not so much. The caps I specifically referred to, polystyrene and polypropylene, differ from a theoretically "perfect" capacitor to such a slight degree that if critical listening detects a difference, one would question the listening process more than the difference in dielectrics. I won't discount differences in cap construction and strays to other parts, as they're usually on the large side. FWIW, I've recapped at least a couple things over the years.

 

[Freds.Bands]

FWIW, if I gave you two well made capacitors hidden in black boxes with just the leads coming out, one polystyrene and one polypropylene, matched for value, plus any test equipment you wanted, you'd have a lot of trouble coming up with a test to tell which was which.

You know, I used to do this electrical testing for a capacitor manufacturer. There is a small difference in dissipation factor vs temperature and vs frequency for PP and PS. But in normal use most people could not tell, though some may claim to "hear" the difference. Well when PP and PS are melted, there is a noticeable difference in smell.

 

[Findm-Keepm]

I think Self recommends polystyrene under 10nF and polypropylene over that value due to price considerations (starting page 63 in the section on capacitor non-linearity). Distortion is quite low in polypropylene but even lower in polystyrene.

Actually, throughout his Self on Audio book, he specifies polyester in input stages, and deigns the use of polypropylene.

My copy is dated before his latest book, so he may have changed his ways.

BTW, Self on Audio (at least my copy, a second edition) has more errors than any book I have ever read. Noise is misspelled many times as "noice" - even in the same paragraph. For kicks, I loaned my copy to an in-law that is a copy editor, and he returned it with 47 gross errors marked - and all were non-technical. His comments were "Typical Newnes trash" and "not ready for prime time" - and noted the publisher had no errata page(s) to offer.

Me, I cannot tell the sonic difference between any dielectric, but my hat is off to those that can.

 

[absolon]

Self provides graphs of the measured distortion of polyester, polypropylene and polystyrene in Small Signal Audio Design, and although the difference is quite small and undoubtedly below audible range, the difference between polypropylene and polystyrene does exist. My thought on it and what I understood Self to suggest is that if price is similar, all other things being equal, pick the lower distortion component.

It would appear that Elsevier, who own Newnes, has a reputation for focusing more on profit than they do on dissemination of knowledge. On that basis, it's not a surprise that editing falls victim to cost cutting.

 

[Freds.Bands]

ESF (or power factor (or dissipation factor) at these levels is not "distortion" which is a type of non-linearity effect; but that is just a word. With such a small difference in power factor (or dissipation factor) which is already very very low, I just can't believe it is significant in audio applications, and much less be audible in a complex solid state amplifier where there are so many small errors/distortions. I could see it maybe in Precision Instrumentation applications. (So many legends in audio.)

 

[absolon]

Looking to understand rather than to argue the point.

Self labels his graph axes THD against frequency and minor as they may be, there are differences in his results even if they are low enough to be inaudible with the styrene capacitor showing marginally better. To put it in terms I can better relate to: given a choice for an RIAA capacitor between a Wima FKP2 4.7nF PP capacitor vs a Xicon 4.7nF PS, which is the better choice? Does the answer change if the PP costs 74 cents each and the PS costs 47 cents each?

 

[HypnoToad]

I replaced all the RIAA caps in a CA640P from Wima PP's to Polystyrene's and honestly couldn't tell the difference. Not saying it didn't make a difference or it wouldn't be noticeable with a higher end unit.

 

[absolon]

At some point I'll be trying the same comparison with the 797 stage, I bought the Wimas for it as well as the Xicons.