input/output capacitor uF question...

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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? :scratch:

Thanks in advance for any help out! :)
 
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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
 
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
 
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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. :D
 
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
 
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."
 
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.....


"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.....
 
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.
 
It's a solid state amp with symmetric supplies - there wont be output capacitors. The large white ones are probably high quality polypropylenes used for supply bypassing. They will quite likely be just fine. The large electrolytics may benefit from renewal if the amp is 15-20 years old.

Input capacitors - you will find those on the main amp pcb, near where the cables from the RCA jacks connect. It looks like they are small electrolytics near the opamp in the middle of the board, between the four big blue polyester capacitors.
 
wow, thanks for shining some light on this layout! :)

So, you think those 2 small electrolytics are my input caps? That makes sense now. But, do you think those blue polyesters are in the signal path too?

Would changing the big white caps near the PS have an audible effect if they are for bypass purposes?

Thanks again
 
"The values for power supply capacitance can be realistically determined by a consideration of the numerical value of W C R where W is the line frequency (377 rad/sec), C is the power supply capacitance, and R is the load resistance.

An WCR value of 10 yields about 10 per cent ripple (pk.-pk. ) and a value of 100 has about two percent. Below 10, the power supply will have serious problems and values of about 100 will achieve diminishing performance returns. The minimum value then, for each of the four power supply capacitors should be about 3,000uF and the maximum about 30,00OuF. Capacitances above this value may cause diode bridge failure due to turn-on surges and are not recommended."
 
the belief system that leads to using DC servos usaully means the designer won't use electrolytic caps in any signal application

they might be local power supply filter caps for the op amp for the servo - few go to the trouble of using a DC servo and then then aslo use electrolytics in them
 
Well, I finally got a schematic for this amp! Had to contact Magnum Dynalab about it...they sent me an owner's manual with it also, for free. Very kind of them.

I had to scan it in and merge the 2 pages, but I think I got it looking pretty good. I will upload it on here...if anyone wants a full size copy, let me know and I'll send you one.

Can anyone tell me if there are any capacitors in the signal path of this amp?

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