polypropylene capacitors

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#127
The only data I can offer is for a 180nF polycarbonate cap I measured:
polycarbonate-180nF.png


Which is at the analyzer floor for distortion (the rise on the left is due to noise). So I predict they will be basically equivalent, other than polycarbonate not being made for decades...
The measurements would have been made in a divider with a resistor of similar impedance at the test frequency.
 
#130
Polycarbonate caps can be more compact that polypropylene caps, as the base film has less "give" and can be wound tighter. The same is true for polyphenylene sulfide caps. There are some notable exceptions to this - the yellow Philips polycarbonate caps tend to be on the "huge" side of the scale, perhaps because of the standard case used to encapsulate the part. Polycarbonate caps can also be made with voltages ratings as low as 50VDC, so the capacitors can be more compact. I have some Bishop Electronics 50V, 1uF polycarbonate caps that are very compact. Bishop has since been snapped up by Electrocube.
 
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#132
Keep in mind that polycarbonate caps are either wrap-and-fill, or encapsulated with epoxy in boxes - they don't have their dielectric film hanging out in the breeze like polystyrene caps, which are attacked aggressively by solvents like acetone. As long as you confine yourself to cleaning boards with milder solvents like isopropyl alcohol, things should work just fine. If you are working in an environment with aromatic solvent vapors (which do attack polycarbonate), I wouldn't willingly hand around long. If you are expecting circuits to hold up in an environment like an oil refinery, polycarbonate may not be the best choice for a dielectric. However, they work just fine for me at home.
 
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#133
There are also boxed polystyrene caps - ex soviet K71-7 but with very low values around 9 nanoF, up to 250 Vdc. Better construction than classic axial polystyrene's.

LCR made some up to 50-63 Vdc low values also ( Farnell may have some - didn't check last two years ).

S+M also.

Not in manufacture long ago.
 
#134
Actually, I have some encapsulated Soviet 0.1uF polystyrene caps, as well as some 2uF polystyrene wrap-and-fill caps from one company of the many (I forget which one in particular) in SoCal that made film caps back in the 70's. I also have some Soviet polystyrenes that were potted in aluminum cans.

Having said that, though, the classic barrel-style polystyrene caps with laid-in leads will become a sticky mess if they get an acetone bath...
 
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#135
K71-7 ex Soviet polystyrenes are in green & green-yellow boxes, 0,5 & 1% low values, good for RIAA networks in tube preamps.

Accidentally having 0.01 uF K71-7's saved me a lot of money comparing to buying 1% parts in Mouser ( KP1830 film/foil stacked construction ), for my current build ( even if KP1830 are maybe probably better ).
 
#136
I always clinged to MKP not even respecting MKT.

But now I have some nonpolar electrolytics of 235uF, combined from 2x 470uF, 100v and they sound perfect for a 6db crossover of a small fullrange.

Very low distortion, crisp impulse response, everything fine.
 
#139
Max Headroom -
I haven't auditioned one type of offset reduction vs. the other. I thought the film cap approach was so compelling that I have used it as a default approach since the late 70's. It's the reason I commonly use jfets or mosfets as the input diff pair for my amp designs, as they can tolerate the 1M unity feedback resistor without undue offset issues due to bias current. I am considering doing a layout to implement Nelson Pass' AB100 design, which does have an electrolytic in the feedback loop - maybe that will be where I do a listening test. Having said that, it will have a Philips 10uF MKC cap as input coupler, to work with the 20k or so input impedance on the input side of the bipolar diff pair (KSC1845). Got to balance those bias current offset voltage drops...
 
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