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Polystyrene cap question

Mat86

Mat86

Active Member
So I over the last week I ended up with two completely opposing take on some capacitors that has left me scratching my head.

I was recently re-capping a DAC (don't ask) and someone (Guy #1) pointed out that the manufacturer was using polystyrene capacitors and that I *need* to replace them all because, basically, "they're crap". However, I searched online and found them to be pretty widely used in audio.

Once I recapped the electrolytics, the manufacturer soldered a few from both ends and my dumb hands accidentally made contact with two poly caps and part of my iron at some point - singing/melting the plastic casing on top. Guy #2 who saw this then told me that both caps are now absolutely "dead", 'but it wont affect anything you could hear anyway.'

Both caps are near the output of the board, seemingly "102J" so my chart says 1000pf. Everything functions but it's eating away at me.

a) Are polystyrene caps bad, or can they be dead and still not affect a thing? Which is it
b) Would they actually die just from heat contact or would they need to be really burnt up to fail?
c) Should I replace them with some silver mica caps, or leave it be?

(I realize without schematics this isn't entirely something I can look deeper into, just asking broad strokes here)
 
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However .. Precautions need to be taken . They don't take kindly to extreme heat & vaious chemicals .. Don't use acetone around them..;) Even the soldering can be damaging if not done quickly . I use a " clip on " soldering heatsink ..;)
 
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avionic said:
Hell no...Probably one the most reliable caps in there.. I do not even..think about replacing them unless they are physically damaged. If damaged I replace it with a new polystyrene..
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would this type of damage be concerning? or live and let be?

link

Only reason I mentioned silver mica was because it's what a local store has in stock for 1000pf radials
 
I would replace it, not a good idea to have the case open to the air.

Probably still works fine, doesn't look like the layers got shorted.

Polystyrene caps are probably the closest to ideal capacitors in those sizes, but they are VERY heat sensitive -- you can melt the metal coated sheet while you solder them in, so they cannot be used in most wave soldered or infared soldered boards -- they will melt.

If they are shorted internally they will definitely affect the circuit, and not in a good way.
 
You can try the mica's. Worst case --sound degridation.
Mat86 said:
Guy #2 who saw this then told me that both caps are now absolutely "dead", 'but it wont affect anything you could hear anyway.'
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If they were "dead" it would definitely be noticed.
 
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I'd never replace a polystyrene cap unless it was actually defective. As above, they can be damaged by heat and by solvents. Flux removers can wreck 'em. If you see fine crazing of the clear plastic, that's a sign of solvents. Still, if the thing works OK, the caps are likely OK. There isn't much better than a polystyrene caps with regard to sonics. You need smarter minions.
 
I would replace the one(s) in the picture with new polystyrenes but that just my ocb talking .

"What I'd like to know is who are Guy #1 and Guy #2? They both sound woefully ignorant." Doug .

I don't would just ignore what they were saying anyway , OP knows who they are and should probably do the same .
Just my 2 Cents regards F.
 
I wonder if Guy #1 and Guy #2 have both made the same mistake and arbitrarily extended the science (& folklore :) ), about the notorious 'Black Flag' capacitors (which are Polystyrene, and are unreliable) with other ordinary Polystyrene capacitors? - This is due to a number of possible factors including but not limited to:- Manufacture, Construction, Locations when in use, Criticality of failure if they do go faulty.

:dunno:
 
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The Black Flag caps failed due to shrinkage of the casing causing the leads to separate from the film if I remember correctly, not from any inherent problems with polystyrene as a component.

Claiming they are all "bad" is like claiming that all small signal transistor are "bad" because the early designs used in a lot of 70's amps have failed with time.
 
the trick is you have to measure it to make sure it hasn't shifted value. That can happen when they get subjected to heat.

otherwise as above, good caps electrically, just fragile in some ways.
 
Doug G. said:
What I'd like to know is who are Guy #1 and Guy #2? They both sound woefully ignorant.

Doug
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Oh just two random experts on an audio/DIY discord

cannext said:
I would replace the one(s) in the picture with new polystyrenes but that just my ocb talking .

"What I'd like to know is who are Guy #1 and Guy #2? They both sound woefully ignorant." Doug .

I don't would just ignore what they were saying anyway , OP knows who they are and should probably do the same .
Just my 2 Cents regards F.
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OCD talking to OCD ;)

(Yeah I put #2 on ignore, seemed like a real piece of work full of bad or overly critical takes, like leaving too many fingerprints in my chassis or needing to glue a small cap down to prevent damaging vibrations...)

gadget73 said:
the trick is you have to measure it to make sure it hasn't shifted value. That can happen when they get subjected to heat.

otherwise as above, good caps electrically, just fragile in some ways.
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and potentially damage it with heat to remove and test it....kind of a Schrödinger's Cap situation ;)

w3jn said:
Nicking a polystyrene with a soldering iron doesn't necessarily mean it's destroyed. If it measures OK and works OK, it's most likely not worth going thru the hassle of ordering a new one and replacing it.
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Everything definitely works & sounds okay to my ears, A/B toggling it with a different DAC on the same amp, unless the damage is on some micro detail level

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Thank you everyone for the replies & help
 
I would just replace Guy #1 and Guy #2.

PS - (not polystyrene) - in full disclosure, I know very little about caps.
 
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