Pioneer A400 Power supply Caps - diyAudio
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Old 2nd May 2012, 10:18 PM   #1
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Default Pioneer A400 Power supply Caps

Hello all, previously been a lurker finally joined now I actually have something to ask - I've a-level physics knowledge so, I can take a reasonable amount of technicality in answers but my dad's decided to replace the four 15,000F slit foils in his original cyrus PSX, they're not damaged/ non-functional to the best of our knowledge, and as although they're 5 pinned caps, only two pins are connected in the circuit, could two of these replace the two 10,000F electrolytic's in my Pioneer by means of an experiment [both are rated at 50V] for a possible improvement or will the greater inrush current likely fry the rectifier?

Thanks, James
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Old 2nd May 2012, 10:22 PM   #2
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It's probably fine
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Old 3rd May 2012, 04:17 PM   #3
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I was in a rush when i posted this last night, apologies. Just checked the datasheet on the rectifier [d5sb20] 6A rating with heatsink, 2.8A without, seems like it should be fine, currently running without a heatsink but, i guess if it does blow i'll be forced to upgrade to something a little fancier, so long as nothing else pops in the process, Thanks ticknpop!
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Old 3rd May 2012, 04:59 PM   #4
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Incidentally could anyone recommend any shottky diodes which could suitably replace a d5sb20? [ http://www.datasheetcatalog.org/data...en/mXxsyus.pdf ] I'm looking but current matched diodes I've come across so far don't seem to have the required voltage characteristics to be suitable.
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Old 3rd May 2012, 05:29 PM   #5
AndrewT is offline AndrewT  Scotland
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Keep the existing rectifier/s.
Try the replacement capacitors.
Try to allow for returning to near original, if the experiment fails.
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regards Andrew T.
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Old 3rd May 2012, 06:04 PM   #6
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One thing at a time, good idea, Thanks! I'll post [subjective] results after i get hold of the new caps, and see where I stand.
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Old 27th May 2012, 04:59 PM   #7
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After 7 hours of fiddly labour I've just finished, fitted two 15,000F 50V slit-foil cyrus psx capacitor in place of the two 10,000F Pioneer ELNA electrolytic PSU caps, and i've disconnected one of the input on the back from the selector switch and wired it straight the the volume pot with 5A [i think, its all i had available] solid core copper wire. The difference really is night and day, bass is stronger and more 'full' sounding, I think a slight bit deeper, there seems to be less noise at the speakers with no source playing and the sound as a whole feels to have opened up, sound more airy, and at the same time taken on a sense of 'effortlessness' which wasnt previously there, so thanks for the heads up gentlemen, first major Hifi mod a success! Incidentally i also replaced the 4 caps inside the cyrus PSX with ELNA electrolytics, so replacement of those is perfectly possible for anyone reading this in future, 3 of the capacitors 5 terminals are for mechanical support.
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Old 27th May 2012, 08:57 PM   #8
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Looking at the A-400 schematic, I'd say your imagination is helping out with the sonic improvements - expectation bias in full swing. With these two mods, something like a lower noise floor is close to impossible (at least if the volume pot is still active, which I assume it is). Anything else would require a selector switch in need of a good cleaning (which isn't even unrealistic but should have shown as intermittency) or the original caps to be pretty much flat with dreadful ESR (not all that common with these big ones, which usually are of decent quality and in many cases don't have an overly hard life in home hi-fi amps; anyway, I would have expected noticeable hum under any kind of loading then).
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Old 27th May 2012, 09:48 PM   #9
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Is this to say any changes I've noticed following work on the amp are primarily psychological? I find it interesting that characteristics of the low frequencies following the change remind me of the same differences noticed when a PSX [which the caps are salvaged from] is added to a cyrus two. Still, a psychological change is as big as any measurable difference [or so I believe].
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Old 28th May 2012, 05:38 AM   #10
sbrads is offline sbrads  United Kingdom
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The big test is to put the old caps back into the Pioneer to see if the sound quality goes back down to what you remember. Somehow, I don't think we'll be seeing a post from you saying you've tried this
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