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Are "audio grade electrolytic capacitors" snake oil?

SIY

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I have a question and I hope it does not come off as too ignorant. I have wondered for years how electrolytics could be
used just for ac signal work as in a crossover. I thought they needed DC bias to maintain the thin dielectric layer on the plates.
Just for stability and low loss poly seems way better to me. Thanks in advance if anyone can answer this!
Usually, the electrolytics used in crossovers are bipolar, i.e., they're connected in series back-to-back (internally) so they can be used with AC.
 

Wombat

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Thanks Tks for living down to the typical attacks too common on this forum. If your little missive is representative of your idea of an honest conversation, NO THANKS.

Pause and reflect time:

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We(ASR, generally) are 'all ears' when it comes to new scientific evidence. Not so much for unsubstantiated, ''but I hear it", claims that go against more validated knowledge. You have to do better.

Don't make it personal as it is all about impersonal proof.

Don't%20tell%20anyone.gif
 
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halcyonian

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And we hear from more of the armchair expert dogma crowd.
Did they ever convince you to take the "science juice"?

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Apologies for necroposting, however I'm looking at recapping a couple of units.

Looking to order all Kemet caps for both PSU and amp/audio boards, since the specs are better than Nichicon "audio grade" on Mouser and they cover the range of what I need. The performance specs I'm most looking at are ripple current and hours ratings, along with making sure all are 105C+.

Does that sound like a reasonable route, to go on specs alone? I'm not torn either way on audio grade vs. caps with better specs, so it's not a trick question.
 

fpitas

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Did they ever convince you to take the "science juice"?

-------------------------

Apologies for necroposting, however I'm looking at recapping a couple of units.

Looking to order all Kemet caps for both PSU and amp/audio boards, since the specs are better than Nichicon "audio grade" on Mouser and they cover the range of what I need. The performance specs I'm most looking at are ripple current and hours ratings, along with making sure all are 105C+.

Does that sound like a reasonable route, to go on specs alone? I'm not torn either way on audio grade vs. caps with better specs, so it's not a trick question.
Yes. Kemet is a reliable manufacturer, with a lot of history. Probably the caps you get will meet or exceed the specs.

Honestly, Nichicon is good. But if Kemet specs better, I'd get those, too.
 

AnalogSteph

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Looking to order all Kemet caps for both PSU and amp/audio boards, since the specs are better than Nichicon "audio grade" on Mouser and they cover the range of what I need. The performance specs I'm most looking at are ripple current and hours ratings, along with making sure all are 105C+.

Does that sound like a reasonable route, to go on specs alone? I'm not torn either way on audio grade vs. caps with better specs, so it's not a trick question.
Look at what the caps actually do. For filter / decoupling, your approach is sensible enough. If physical size permits upping the voltage rating, do that. (If that gets you to more than three times the regularly sustained voltage, you can think about increasing capacitance as well.) QC wasn't the same 40+ years ago, so parts back then tended to have substantially bigger margins, often sustaining voltages of multiple times their nominal rating in order to minimize the chance of getting a bad apple. These days the statistical distribution would be much narrower and the average much lower. That's a good part of why they have become a fair bit smaller.

There's a few extra gotchas. For one, ESR tends to be inversely correlated to leakage current, and leakage current relates to life expectancy in a lightly-loaded scenario. So while extra low ESR parts will stand up much better to abuse inside a SMPS and e.g. last 5-7 years where others might only make it 2, in a less rough environment they might start to fail after little over 10 years while a quality standard part would last 25+.

Leakage also is generally undesireable in applications such as coupling capacitors. Now parts quality has substantially improved over the decades to the point where even a moderately low ESR series like Panasonic FC is quite suitable as an all-round audio capacitor. However, when the original is like a 4.7 µF, a closer look is probably warranted. (If you ever come across an ultra low leakage type, generally orange and most often found near the stereo decoder in a tuner, these very rarely fail. Which is all the better, last time I checked there wasn't more than one or two series of such parts left, so it's a pretty niche thing. These can sustain seeing no substantial DC voltage for decades on end.)

There's also a few tricky cases. Coupling capacitors used to drive low(er)-impedance loads need moderately low ESR, and what remains should be sufficiently linear as well. Audio-grade parts may well be worth it in such an application. And then there are those larger capacitors (often 100-220 µF, sometimes more) at the foot point of feedback networks with the nigh-impossible task of being lowish ESR, very linear and lasting for decades at mere millivolts of DC while often being rated as low as 6.3 V. (The thinner the oxide layer, the easier it is to poke holes in it, and it tends to degrade if kept discharged.)
 

wwenze

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Did they ever convince you to take the "science juice"?

-------------------------

Apologies for necroposting, however I'm looking at recapping a couple of units.

Looking to order all Kemet caps for both PSU and amp/audio boards, since the specs are better than Nichicon "audio grade" on Mouser and they cover the range of what I need. The performance specs I'm most looking at are ripple current and hours ratings, along with making sure all are 105C+.

Does that sound like a reasonable route, to go on specs alone? I'm not torn either way on audio grade vs. caps with better specs, so it's not a trick question.

Just take note, if it's a SMPS, don't change its capacitor unless it is spoilt, and if you change it don't use "audio grade capacitors"
 

halcyonian

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Taking into account the feedback here (thanks all!) and my desire for maximum performance and longevity, I ended up springing for all polymer caps and some film caps (for smaller values) to replace all electrolytics in a NAD 2600PE (Japan).

Something didn't seem right about going the general brand, well-rated spec, route for electrolytics when the OEM were all Nichicon and Rubycon, from what I've observed. In addition to poly caps, I also made a BOM for Wurth (excuse the lack of diacritical marks) electrolytics and picked up a set of those to compare / measure actual readings against the others. Also, if I made any errors with part sizing, I'll have spares to fall back on. The Wurth caps look good on paper, especially lifetime ratings, however the jury seems to be out on if they're actually durable like the other components they brand.

If this works out well, I plan to do the same refurbishment by using poly caps in other amps. It's not the cheapest route, of course, and perhaps there are other reasons currently unbeknownst to me as to why this isn't the best thing to do.
 

Killingbeans

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If this works out well, I plan to do the same refurbishment by using poly caps in other amps. It's not the cheapest route, of course, and perhaps there are other reasons currently unbeknownst to me as to why this isn't the best thing to do.

Depends on whether or not the ESR value of the cap is critical for stability in the specific design.
 

DonH56

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Large electrolytic capacitors in the power supply offer much greater capacitance for their volume and are far cheaper than equivalent film capacitors IME. Smaller bypass capacitors can be ceramic, electrolytic (often tantalum), or film and should do just fine. Coupling capacitors are the only place film types may offer better performance (though even that is questionable; depends upon the circuit).
 
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