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Chip Amps Amplifiers based on integrated circuits

My_Ref Fremen Edition - Beta build/Fine tuning
My_Ref Fremen Edition - Beta build/Fine tuning
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Old 10th August 2012, 05:10 PM   #1491
bcmbob is offline bcmbob  United States
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WARNING - Dario pointed out the caps in post #1488 are not the correct spec. Those are Silmic II and not RJK. Not sure how much difference there is but, be aware they are not what is in the BOM. They are quite usable in those positions, just not the same. I ordered some so I'll try them out and report back.
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Old 11th August 2012, 12:05 AM   #1492
soongsc is offline soongsc  Taiwan
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One thing I can't understand is that why people choose polarized caps for a position that does not have DC offset? We don't to that in speaker XOs, why do we do it here?
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Old 11th August 2012, 01:32 AM   #1493
bcmbob is offline bcmbob  United States
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I believe that is one of the topics proposed for experimentation during the RC process. There will probably be several more.
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Old 11th August 2012, 09:34 AM   #1494
AndrewT is offline AndrewT  Scotland
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Soon,
the input DC blocking capacitor and the negative feedback, DC blocking capacitor locations, both have a DC offset. This is usually checked for during design and checked again at assembly time.

Have you never bothered to measure the offset on your polarised capacitors?
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Old 11th August 2012, 11:16 AM   #1495
soongsc is offline soongsc  Taiwan
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Andrew, I think you are referring to something different from what I am talking about.
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Old 11th August 2012, 12:08 PM   #1496
AndrewT is offline AndrewT  Scotland
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Quote:
polarized caps for a position that does not have DC offset
Which polarised (electrolytic) capacitors are you referring to?
PSU, Decoupling, Coupling, DC blocking?
As far as I can see, all of these locations in the MyRef have a polarisng voltage applied to the capacitor.
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Old 11th August 2012, 05:31 PM   #1497
soongsc is offline soongsc  Taiwan
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DC voltage needs to be such that polarized caps are never reverse polarized in operation. In MyRef, C9 really has no such voltage. Many chip amp applications implement the same way as well. Very curious about the considerations behind this.
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Old 11th August 2012, 08:32 PM   #1498
AndrewT is offline AndrewT  Scotland
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Originally Posted by soongsc View Post
DC voltage needs to be such that polarized caps are never reverse polarized in operation.
that is not a requirement.
Prevention of excessive reverse polarity is a requirement.

As far as I know electrolytics can tolerate 1000mVk to 1500mVpk of reverse polarity without suffering any degradation.

If you apply a 1Vac signal to an electrolytic coupling cap and it has 200mVdc offset then the worst case short term reverse polarity is ~1200mVpk.

But the capacitance of the capacitor does it's best to drag the undriven plate along with the voltage on the driven plate. That 1Vac signal can't actually apply anything like a 1200mVpk reverse polarity between the plates.
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Old 12th August 2012, 01:29 AM   #1499
soongsc is offline soongsc  Taiwan
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So what about asymmetric leakage current?
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Old 12th August 2012, 11:04 AM   #1500
AndrewT is offline AndrewT  Scotland
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Would that appear as different from the AC signal that is coupled across the capacitor?

I don't know because I have never heard of that before.
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