differences of TYPES of caps in CMOY
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diredesire

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Greetings, i've been spending most of my night researching this on tangent's site (and the links on there) and searching through the forum but haven't found any really good info on my specific question...

I have an EE store at my school which supplies basic parts, and i've been building a few CMOYs for myself and hopefully for sale to some of my friends (no one around here that i know is really into higher quality audio...)

My question is regarding TYPES of caps and their performance as an input cap on the CMoy circuit. I'm looking at getting .22uF caps or slightly higher (.47uF max)

The types of caps i have available to me are listed here:
http://www.ee.washington.edu/stores/
(Click on online-product catalog)

For those too lazy to click, they're listed as:
Capacitors, Ceramic Disc
Capacitors, Electrolytic
Capacitors, Monolithic
Capacitors, Polyester
Capacitors, Polystyrene
Capacitors, Tantalum
Capacitors, Variable

I know to avoid (from what i've been reading) the Ceramic type and the Variable type. I know on the input side that Electrolytic spells trouble for me, but i have NEVER seen discussion of the Monolythic, or Polystyrene... I am looking to stop by the school's store tomorrow, and i know the Polyester caps are ACCEPTABLE but i was wondering if any of these other types (Tantalum, polystyrene, monolytic etc) are of higher quality that i should get... Most all of these are available cheaply to me, so i am willing to experiment. I'm looking for a fairly compact solution, so even if one of these are better, space is an issue... I'd be very grateful for any sort of help i can get!

Thanks guys!
-dd

Edit: from one of the links in Tangent's site, i read that polystyrene is good, but isn't readily available at higher capcitances, and it looks like my school has them in sizes up to 7500pF (is that 7.5 uF?) for 600V
, i'm guessing those will be HUGE. It doens't look like they stock polypropylenes, do they go by another name?
 
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amb

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Tantalums and "Monolithic" (also known as multilayer ceramic) are suitable for power supply bypassing but not good for audio signal coupling. This leaves polyester (also called "mylar") or polystyrene in your list. Polyester is "ok" but not great as coupling caps, it is the poorest performing of the "plastic film" types. Polystyrene is very good but they're physically large for the capacitance. I would be surprised if you could find a polystyrene film cap in 0.22uF or larger. Also, polystyrenes are becoming scarce because most capacitor manufacturers don't make them any more.

The other excellent coupling cap types are polypropylene, teflon and polycarbonate. The latter two are also hard to find now. Metallized polypropylene caps in 0.22uF 100V can be found in reasonable sizes (such as the Wima MKP2 series), but the non-metallized ones, or those with high voltage ratings are also typically quite large.

Edit: 7500pF is 0.0075uF.
 
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