Saturday, 5 October 2019

Ceramic vs. Film Capacitor: Which one is preferred in audio circuits?


I'm considering building an amplifier following instructions from a MAKE magazine article.



However, as I was reading the circuit schematic, I noticed that the author denotes that the capacitors C101, C104, and C105 are supposed to be "film capacitors." Is there a reason as to why one would use film instead of ceramic capacitors in this application? Also, if a website denotes "metal film capacitors", is that the same as a "film capacitor"?


Right now, the only difference I know of in types of capacitors is that electrolytic capacitors have a polarity, while ceramic ones don't. I was wondering if film vs. ceramic has a similar differentiation.



Answer



"Film Capacitor" typically denotes polyester or polymer film as the dielectric - as another answer points out, metallized film capacitors are the same thing: A metallic coating being applied to an extremely thin polymer film, to create the conducting electrodes of the capacitor.


In general, ceramic capacitors are somewhat non-linear in their frequency and voltage responses, compared to film capacitors. Another issue with ceramic capacitors is that they tend to behave as microphones, thus picking up ambient sound and modulating the voltage across them accordingly.


Also, for smaller values (a few pF), ceramics were more commonly used, while larger values were somewhat likely to have film considered as an option - or at least that was how it used to be, before capacitors became so inexpensive with the advent of SMT, that the price difference became negligible except for huge volumes.


Both film caps and ceramic ones are non-polarized, so that isn't a difference.


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