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Old 12th August 2005, 04:28 AM   #1
winslow is offline winslow  United States
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Default Power supply capacitance

Is there a such thing as too much? I know little about power supplies is the reason I'm asking. I have a couple supplies from a couple donor amps that I'm going o build Mini-A boards for, and they have 2 2200uf caps on them. I was thinking that when I ordered the parts from Digikey to stuff the boards, I could get a few Panasonic FC 4700uf caps to replace the ones I have. That would increase the capacitance nearly 5x. Which I think would be a good thing...sort of like money and heatsink area- never can have too much (read that tonight, and quote stuck out to me).

Thanks, sorry for having such newb questions.
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Old 12th August 2005, 08:49 PM   #2
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No, there is not really such a thing as too much, and if there
was it would be a lot more than what you're talking about.

It is true that using high capacitance stresses the rectifier
bridge and occasionally pops a fuse on turn on, but that can
be fixed with a heavier duty bridge and an inrush thermistor
easily enough.

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Old 12th August 2005, 09:19 PM   #3
JohanH is offline JohanH  Netherlands
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Winslow,

you will experience that there are many opposing opinions about PSU capacitance.

Some will say x is not enough whilst others will argue that depending on amp topology y will be more than enough.

I have not built any Pass-like amps but I tend to agree with Nelson: you cannot have too much but you'll have to consider inrush currents etc. and design your PSU accordingly.

For example: I have built several class A Hiraga amps but never had a PSU with less than 1F (that is 1.000.000 uF). The first one I built would visibly dim the lights in the house when switched on.

There is somewhere in this site a thread where it is argued that low ESR is more important than high capacitance in the PSU. As low ESR capacitors tend to be much more expensive than regular ones I have not tried this in practice myself.

For your purposes; stuff in as many low esr capacitance as you can fit and listen to the difference yourself. I'm sure you'll be amazed.
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Old 13th August 2005, 12:02 AM   #4
winslow is offline winslow  United States
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Thank you. I'm going to use either Panasonic FC or FM caps. Both have low ESR and the FM are super low ESR. Not trying to get super esoteric on the parts right now since the budget is sort of limited and I want to be able to get all the parts from one source...and Digikey has the rest, so I'll get whatever Digikey has.

I'll do more searching on the suject. Did some last night, but I can't seem to narrow the search down enough with this search engine.
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Old 13th August 2005, 12:53 AM   #5
BWRX is offline BWRX  United States
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those caps are also very popular for use in power supplies for other low wattage amps (SI, AMP3, and other class D offerings). it seems you've found two of the three low ESR caps offered at Digikey. the third would be Nichicon's HE series. similar to the Panasonic FC series but with very slightly less ESR and a lower price. also, the FM series has an upper capacitance limit around 1800uF or something while the FC and HE go up to 4x higher.

a bunch of good quality low ESR caps in parallel is often better than a couple of large value caps in terms of both cost, performance, and physical volume.
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Old 13th August 2005, 01:54 AM   #6
winslow is offline winslow  United States
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I didn't know about the Nichicons, but I'll take a look into those as well. I put some FMs in a Bel Canto DAC2- power supply and decoupling...changed out diodes to HexFREDs, etc. But I haven't got her back together yet, so no comment on the sound. But I'll probably do the same to my Benchmark DAC1 as well.

Thanks for the tips.
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