What BIPOLAR (crossover capacitor) to choose? From the past or modern - diyAudio
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Old 13th August 2014, 05:47 PM   #1
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Default What BIPOLAR (crossover capacitor) to choose? From the past or modern

I am about to replace an 3.3uF and an 8.2uF that are out of specifications over one Philips crossover of 90s.
The capacitors were measured by an LCR meter and the results are pictured below.

There are few things that they do confuse me and therefore this topic is here to serve it purpose.


It seems that both capacitors are made by ROEDERSTEIN and both belong in the era of 90s.
My problem about selecting alternatives starts from the fact that newly made Japanese capacitors does not come any more at 8.2uF

Also there is more modern Panasonic capacitors which has half the size of the ones that I have, and this is also one detail that extends my confusion.

As third detail I will mention that now that I own a true LCR meter, I have the fear that this New – Old stock of ROEDERSTEIN on eBay, there is a chance to not have tight specifications.

The plan is this pair of crossover to serve for another 15 Years as trouble free.
What makes me scratching my head from confusion is that my pair of speakers even If I own them for 20 years they should have perform for no more than two months continues use (24/24) at 50% of their power (150W RMS) and about 48 hours in total at full power.

Therefore I can not justify this capacitors damage from over use.
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File Type: jpg capacitors-close-up.jpg (150.9 KB, 68 views)
File Type: jpg FB815-crossover_3.3uf.jpg (279.4 KB, 69 views)
File Type: jpg FB815-crossover_8.2uf.jpg (298.8 KB, 68 views)
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Old 13th August 2014, 06:09 PM   #2
Mooly is offline Mooly  United Kingdom
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Hard to see how a cap can increase in value from under 10uf to nearly 100uf.

Are you sure the meter is telling the whole story ? Have you tried other bi-polar caps to confirm ? Have you guestimated the caps value by more traditional means as a further check ?
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Old 13th August 2014, 07:39 PM   #3
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I am saying the whole story , but there is some more info that come up before few minutes, by discovering the words .. capacitor reforming ..

I started electric shocks at 35V DC by reversing the polarity its time, and this capacitor some how recovered back at a more reasonable value and ESR.

My next plan is to feed it with 35 AC for some time so it internal chemistry to fully wake up, so to check it capacity again.
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Old 14th August 2014, 12:33 AM   #4
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It seems that after some hours of experiments, there is not other improvement possible.
Therefore as I aiming tight tolerance in uF I am open for suggestions of good capacitors in that range, for example has any one try those Jantzen standard version ?



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Old 14th August 2014, 06:30 AM   #5
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Kiriakos View Post
I am saying the whole story , but there is some more info that come up before few minutes, by discovering the words .. capacitor reforming ..

I started electric shocks at 35V DC by reversing the polarity its time, and this capacitor some how recovered back at a more reasonable value and ESR.

My next plan is to feed it with 35 AC for some time so it internal chemistry to fully wake up, so to check it capacity again.
I still think (if only for your own satisfaction) that you should try the caps in another circuit to "prove" there value.

I'm afraid I've no suggestions on replacements beyond looking at component suppliers and what is available.
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Old 14th August 2014, 07:07 AM   #6
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Those capacitors have nothing to prove, if their true value is higher than the specified ,Tweeter and Mid-range are in danger to burn.

If ROEDERSTEIN made capacitors at 90s with such terrible tolerance I can not trust them again.
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Old 14th August 2014, 07:14 AM   #7
Mooly is offline Mooly  United Kingdom
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That's fine

I just wondered if it was more an artefact of the measurement device rather than the fact the cap really had increased in value so much.
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Old 14th August 2014, 07:38 AM   #8
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I have no doubt for the measurement, something happened in that capacitor, at my first attempt to feed it with 35DC the ampere meter from the power supply it jump up to 1A and fall, this happened just once.
After this event the capacitor started to behave normally with leakage current 140mA and the 3.3uF (4.7) has 60mA leakage current, tested another three used BIPOLAR and shown similar leakage current.


Even use my Oscilloscope to data log the discharge curve of this supposed 8.2uF (12.8) and even compared that with the 3.3uf (4.7) everything was great regarding discharge time and curve, the results was as expected.
Then use an analog multimeter to test the discharge in Ohm mode, everything great too.
They are working but they are not perfect enough.
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Old 14th August 2014, 07:49 AM   #9
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Leakage current should be in micro amps ? but yes, I fully understand you are not happy with these caps. But what to replace them with......
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Old 14th August 2014, 09:26 AM   #10
Elvee is offline Elvee  Belgium
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Ordinary mylar are vastly superior to any bipolar cap, and they are cheap and easy to find in this range of values.
If you are not satisfied with the 5 or 10% tolerance, you can always select them.
No need for "audiophiles" caps there (and anyway, when is there actually a need for such caps?)
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