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Old 26th June 2006, 04:49 PM   #1
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Default DoZ power supply


My Death of Zen amplifier's power supply currently uses 2 37000uF Sprague Powerlytic 36DX capacitors per channel (so 4 in total). However, I'm not totally happy with this solution. The caps are quite big. They're rated at 75v, while the power supply delivers less then 35v. And they provide relatively little capacitance for the space they occupy.

So I'm considering replacing them by several smaller caps I found on eBay. These are also Spragues, rated at 17000 uF and 55v (82D series). Since they are a lot smaller, I can put more of them in the amps' enclosure. I was thinking of using 8 of them per channel, combined with some other Spragues I have lying around (2x 20000 uF and 40v). That provides 156000 uF total capacitance per channel, way more then I currently have, and it would reduce the ripple voltage to < 0.1v (quiscent current = 1.5 A).

But, would increasing the capacitance to this level be a significant improvement? How much capacitance do I actually need? From what I read here, 2x 37000 uF seems to be a lot allready. Has anyone tried increasing the capacitance of a class-A amp, and did it have any (audible) effect?

I'm using a single toroid transformer for both channels, which is rated at 250VA (2x25v).

Thanks in advance.
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Old 26th June 2006, 09:49 PM   #2
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Often times power supply caps are chosen for their ripple current rating rather than the capacitance. I suspect there is very little ripple voltage already, so don't make any change until you know the ripple current rating of the alternative caps.
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Old 27th June 2006, 02:43 PM   #3
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OK, but wouldn't the ripple current rating also improve from having many smaller capacitors instead of a few big ones?
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Old 14th July 2006, 03:58 PM   #4
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Well, the time on that ebay item is over, and I'm thinking of re-applying my 37000uF monsters again .

But another matter concering the power supply came to mind: I use a softstart circuit, often seen on this forum (the Elektor design). It works well, but it has a rather long fall-off time (the time it takes for the capacitors to discharge and the relay to fall off). I've already blown several fuses because of that.

I've also seen some other softstart designs (e.g. Rod Elliot's P39). Do these have the same side-effect?
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