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Old 16th April 2012, 05:26 AM   #1
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Default replacement 220uf bi-polar options

I am replacing the input and feedback caps on my acurus A250. C7 is a 220uf 25v non polarized cap. What is the best cap to replace that with these days? It is too expensive to try and replace with a film cap. I have been reading up on Muse es bi-polar or possibly running two Elna Silmic II's in series to make my own bi=polar. one suggestion was to use the Muse and bypass with a film cap. What is the consensus on this?
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Old 16th April 2012, 07:32 AM   #2
amc184 is offline amc184  New Zealand
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My choice would definitely be the Nichicon ES (Muse). There are better options, but not as compact and cheap.
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Old 16th April 2012, 12:56 PM   #3
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here is the schematic, i really would like to implement a dc servo but do not have the knowledge to do so. Anyone care to give me a how to short of that, it looks like ES muse or doubling a pair of Nichicon KZ's or elna silmic II's.

From the schematic, the designer already bypassed these two caps (c2 and c7) with film caps (c1 and c6). Wima MKS caps were used. I am going to replace those as well with WIMA MKP.
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Old 19th April 2012, 03:15 AM   #4
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ok so here is what I have come up with so far.

input coupling cap C2 - 10uf Claritycap ESA
input bypass cap C1 - .1uf vishay MKP 1837

feedback cap C7 - 220uf Nichicon Muse ES
feedback bypass C6 - undecided (possibles: Wima mkp4 or MKP10 or open to suggestion)

c12 .1uf - vishay 1837 or wima mkp4 or mkp10
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Old 19th April 2012, 07:46 AM   #5
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Originally Posted by mfilippello View Post
here is the schematic.....
OK, where is it?

Anyways, you probably won't get much joy from swapping good caps that are not passing or bearing directly on the signal. Your input cap. could be a problem for size and quality. An ideal 10 uF MKP is way big and wortks like an aerial for RFI & EMI but it may be perfectly reasonable to downsize going from electrolytic to film types. Just be careful fitting out with your wish list of bits when size and lead spacings change.
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Last edited by Ian Finch; 19th April 2012 at 07:49 AM.
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Old 19th April 2012, 10:30 AM   #6
AndrewT is online now AndrewT  Scotland
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I used to think that the feedback cap had signal across it and so when a designer said fit this or that in that location I always did what I was told.

Only after joining this Forum did I come to realise that the NFB cap has virtually no signal across it. Measure the AC and/or the DC across the cap if you don't believe me.

If the cap is properly selected to ensure it has no audio signal across it in all normal operation then it can contribute no distortion to the audio output.

If you select the wrong capacitor for the duty then it may have voltage across it and then it may contribute to output distortion.

Self was the first to draw my attention to that and it was following on from his prompting that I came to my current conclusions.

Make sure the NFB cap has no significant signal across it.

Once you achieve that you may come to the same conclusions as me:

I cannot hear the difference in swapping expensive or exotic caps for the normal commercial grade electrolytic in the NFB loop, when that cap is selected to have no significant signal across it.
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Last edited by AndrewT; 19th April 2012 at 10:35 AM.
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Old 19th April 2012, 07:11 PM   #7
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OK, where is it? oops

ok, the input cap now is a 10uf non polar electrolytic. I have been told that this is the most important cap to swap to a film type. My options are either keep using an electrolytic such as the Nichicon ES Muse or change to the Claritycap ESA MKP which is axial and much bigger.(there are better film caps but money was much more) All of the MKP caps are much bigger in 10uf. I know there is the possibility of picking up noise. The questions is, if I shield the larger Film cap to keep noise out, will it be worth the effort over the Muse bi-polar electrolytic option. This cap is also bypassed from factory with a .1uf Wima MKS. I am switching the stock MKS for a Vishay 1837. Vishay only cost $1 so no brainer. The only cap that is expensive is the Claritycap at $20 ea. I need 2. The feedback cap is 220uf NP and will remain an electrolytic and I will be using the Muse BI-polar there. It gets bipassed with a .47uf cap and I will use a Wima MKP4 as it is the same size as the MKS that is there now. The mkp10 is larger so its out. There is also the one other .1uf cap (c12) which I don't know what it does but for $1, it is getting a 1837 vishay
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Last edited by mfilippello; 19th April 2012 at 07:22 PM.
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Old 20th April 2012, 06:56 AM   #8
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Quote:
Originally Posted by mfilippello View Post
OK, where is it? oops

ok, the input cap now is a 10uf non polar electrolytic. I have been told that this is the most important cap to swap to a film type. My options are either keep using an electrolytic such as the Nichicon ES Muse or change to the Claritycap ESA MKP which is axial and much bigger.....
That's true in my experience too.
Thanks for the schematic - some nice features there. The 10uf value is not necessary for an input impedance around 50k so I think you could use a smaller, cheaper part without bass penalty. It is normal to use much higher electrolytic values to avoid the bass distortion they introduce. The bypass cap does nothing to help there but it will probably sound fair, if a little weak in the bass, on its own - try it and listen for deep bass.
Use a 2.2uF MKP there initially, as these are inexpensive and tolerably proportioned. Brand is irrelevant unless you are considering specialty, unique high-end products with stellar prices.
AndrewT's comment on the feedback cap is fair and the issue of no DC across it considered poor in some circles. Many types have been tried there. Why not a Sanyo OSCON? They are rated to only low voltage in that capacitance range but can be protected by a couple of 5c inverse parallel diodes across them - if you fear the output stage may fail and expose it to rail voltage. It hasn't happened yet, apparently
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Old 20th April 2012, 02:25 PM   #9
AndrewT is online now AndrewT  Scotland
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M,
the 10uF is followed by 22k to ground this gives an input filter RC time constant of 220ms.
The NFB is 680r & 220uF. This is a filter RC time constant of ~150ms.

These two time constants have been inadvertently swapped because the designer did not think it important enough to avoid AC voltage across the NFB capacitor.

I strongly suggest you at least listen to the amp with the RC swapped. i.e make the input cap smaller to reduce the time constant to ~100ms.
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Old 21st April 2012, 04:26 AM   #10
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Andrew and Ian, if I put together the advice from both of you, it seems a smaller input cap is the order of the day. I could use a 4.7uf input cap and get a RC time constant of 103.4ms. Does that sound right? A 2.2uf would be 48.4ms. Which would be the better choice?
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