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Old 6th January 2012, 04:28 AM   #1
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Question input/output capacitor uF question...

I have a 200 WPC power amplifier and was wanting to replace the signal input capacitors, but need some info. The cap values are 2uF @ 425 VDC.

Now, I can find exact replacements as far as values, but some of the brands I would like to try only come in 1.8 or 2.2uF values.

My question is, would it be okay to replace the 2uF cap with 1.8 or 2.2uF cap? What problems, if any, would arise from using a 2.2uF or 1.8 cap in place of a 2uF cap?

Thanks in advance for any help out!
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Last edited by Sonance84; 6th January 2012 at 04:32 AM.
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Old 6th January 2012, 04:43 AM   #2
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Either will work.
The larger value will allow a lower frequency extension,But by only a very small percent ( maybe a few hertz or so).
If it were me I would probably opt for the 2.2uf.

For what it is worth.

jer
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Old 6th January 2012, 05:12 AM   #3
jcx is offline jcx  United States
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425 VDC rating is odd for a SS amp that needs +/-60 V for 200 W? - is it single supply??

massive over rating the V of Cap does reduce distortion but oversizing the C, reducing the corner frequency is a powerful distortion reduction approach too

if the amp uses a dual supply a 100 V, 10uF input C might be about the same physical size, may give better performance
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Old 6th January 2012, 05:43 AM   #4
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Quote:
Originally Posted by jcx View Post
425 VDC rating is odd for a SS amp that needs +/-60 V for 200 W? - is it single supply??
I think so...? I have very little info on this amp, but here's a picture to help out.

Click the image to open in full size.
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Old 6th January 2012, 06:19 AM   #5
jcx is offline jcx  United States
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the white 2uF 425 V caps are probably part of the power supply, possibly intended to soak up the rectifier current turn off spikes - look up "snubber"

a multimeter can help find connections when you can't easily follow the trace or wire, to find the input signal path start at the RCA

Last edited by jcx; 6th January 2012 at 06:28 AM.
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Old 6th January 2012, 07:03 AM   #6
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maybe they're output caps then?

A guy on another forum has the same amp and said his output caps had been changed to higher quality specimen...but I thought he meant input caps, so that is my fault for misinformation. He didn't do the work though, so he couldn't elaborate on what was done exactly. Where my big white caps sit, he has Mundorf Supreme Silver/Foils...so there must be something important about those caps. The stock white caps say, "Wonder Caps - Ultima series with Danor" which were some pretty good caps back when the amp was built.

Too bad the designer of the amp, David Belles of Power Modules, does not like to return emails...otherwise I might actually know something about this amp.
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Old 6th January 2012, 07:16 AM   #7
jcx is offline jcx  United States
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schematics are helpful

the photo wiring looks like direct coupled output - you need caps near the size of the power supply caps to AC couple a loudspeaker output

it would be insane to put any signal part in the middle of the power supply/rectifier wiring - huge nonlinear charging current spikes would magnetically couple hum/buzz noise to any sensitive analog signal at that location in your chassis
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Old 6th January 2012, 07:27 AM   #8
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I've heard David Belles will not give out any of his design schematics. I didn't even ask him for those...but just a simple owners manual or basic info on the specs, but I've heard nothing in return after 3 polite emails.

Well, I guess this little 'upgrade' isn't going to happen anytime soon. If those caps are part of the PS, then there's no point in changing them. I was trying to get a little different sound by rolling input or output caps.

The only info I was able to find referring to DC and this amp was this: "DC blocking capacitors aren't used here, but a DC servo loop senses DC voltages on the output of the amplifier and feeds them back to the amplifier's input."
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Old 6th January 2012, 08:22 AM   #9
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the power supply filter caps look skimpy to me, i would look at them instead.......chances are those film caps are still good and there is really no reason to replace them, as they are not likely to get fried nor leak.....unless folks at the other forum tell you that they should be replaced.....


Quote:
"DC blocking capacitors aren't used here, but a DC servo loop senses DC voltages on the output of the amplifier and feeds them back to the amplifier's input."
all the more reason not to replace those.....
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Old 6th January 2012, 09:28 AM   #10
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Quote:
Originally Posted by Tony View Post
the power supply filter caps look skimpy to me, i would look at them instead.......
what do you mean by skimpy...not a lot of uF? should I replace those with larger uF caps?

I don't know anything about amp design, but I do know that some high WPC amps use a ton of uF and others don't...I couldn't tell you why though.

As for this amp though, it has 2 groups of 4 Nichicon 4700uF caps and each group has a Nichicon Muse cap in the center...I'm assuming it's for bypass purposes. That is way less uF than my 165WPC amp, which has 132,000uF total in PS caps.
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