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Old 19th December 2008, 09:48 PM   #1
kop89 is offline kop89  United States
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Default Aleph2 power supply caps

Hi,

I am building aleph2 based on KK-pcb design. The power supply schematic shows 8x 47000 (376000) uF of capacitor PER CHANNEL. This seems like a lot. Can anyone tell me what is the capacitor size used in the original aleph2 design?

Also, does anyone have service manual for aleph 2?

Thanks!
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Old 19th December 2008, 11:57 PM   #2
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The stock Aleph 2 used 4 x 22000uF per channel.
I come from the school of thought that says if some is good, then more is better, and too much is just enough. I rigged my Threshold S-500s with extra capacitance...enough to get them up to a quarter-Farad apiece. I'd have done more, but I ran out of caps. Bummer.
The question of how much capacitance is enough is a matter partly of engineering, partly of sound quality, partly of money. The question of capacitor quality comes into the equation, too. The last couple of times it's come up (at least in threads I participated in) people seemed to get contentious. Must be the phase of the moon or something. I'll bow out now and let others contend to their heart's content.

Grey
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Old 23rd December 2008, 10:04 PM   #3
kop89 is offline kop89  United States
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If HUGE capacitors are a dime per dozen, I wouldn't be here asking this question

If you know where I can get big capacitors at resonable cost, please let me know.

Right now, I am looking at Mouser catalog - a 75V, 22000uF runs about $35-40 each
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Old 23rd December 2008, 10:25 PM   #4
Dansk is offline Dansk  Denmark
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Default Ooops???

If you look at the schematic of the supply, there are two other compenents in it: One with a value of 2,2 uH and another with a value of 4,7 uF. I believe the 8x47.000 uF could be a typo inspired by the above numbers...
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Old 23rd December 2008, 11:00 PM   #5
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Dansk,

The factory Aleph's did not use inductors in the PSU. A lot of DIYer's decided to build CLC rather than CRC power supply topologies. Either way the Aleph circuits sound fantastic. My A30 uses a CRC configuration. This is the most common and lower cost than CLC.

The amount of capacitance does not matter so much. Most people use as much as they can afford or have space for in their chassis. Grey is right in more is better and a person needs to figure out where they are seeing diminishing rates of return for value. Nelson does a good job
at determining if more parts or more exotic parts are actually beneficial in a meaningful way.

Sticking close to the original design as a basis is usually a good choice. Just my $.02 worth.

-David
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Old 23rd December 2008, 11:30 PM   #6
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I must have missed something. Given that the rails in the Aleph 2 are something like 45V, plus or minus a couple of volts, I confess that I'm not clear as to why you're looking at 75V caps. Look at 50V caps, instead. I think you'll find that they're cheaper.
Caps are the sort of thing that surface on surplus sites regularly (unlike big heat sinks). That will also save you a bundle of money. A little patience and a bit of research will generally pay off when it comes to caps.
Hint: When I find a cap that I know I'll need again in the future, I go ahead and buy extras while they're available. By definition, stock at surplus sites tends to be a hit or miss proposition. When they've got what you want, buy it.

Grey
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Old 24th December 2008, 12:58 AM   #7
elac310 is offline elac310  France
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As regards the capacitor voltage, I would personnally keep some safety margin: at "turn on" there can be a short voltage spike, a capacitor ages faster when used near its voltage limit especially in a "hot" class A amp like NP's designs, electrolytic caps are affected by high tolerances etc. I would thus take the next higher standard voltage i.e. 63VDC capacitors, and ideally a 105C version if there is a risk of excessive heat in the amp (no oversized heatsinks, no air holes, hot summers etc).
More capacitance than in the Aleph2 service manual is a good idea (reducing ripple etc.), but bearing in mind that the larger the caps the longer their load cycle and the higher the inrush current at turn on (need for inrush current limiter).

"75V, 22000uF runs about $35-40 each": I find the price is OK, seen from Europe at least; everything is much more expensive here (capacitors, resistors, transformers, heatsinks etc.)
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Old 24th December 2008, 10:48 AM   #8
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Default Some hints

Hello

Big/bigger capacitance is good but, it has some requirements:
you need soft start circuit which is able correctly handle initial inrush current during switch on
properly dimensioned transformer
you need rectifier which is able to survive and handle initial inrush current taken by large capacitors. Per my experience you need minimally 50A rectifier for capacitances higher than 47000uF per rail. Also don forgot put some heatsing for rectifier a correctly dimensioned cables and capacitor bank interconnections.

They are basic rules for me.

Good luck.
Tomas
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Old 24th December 2008, 12:52 PM   #9
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Default Surplus caps

Hi Kop89,

Grey is right about surplus sites. Have you looked at apexjr.com?

http://www.apexjr.com/capacitorsR.html#Computer

15000uF 63V at $3 each.

Cheers,
Dennis
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Old 24th December 2008, 08:09 PM   #10
kop89 is offline kop89  United States
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Thank you Dennis

This is a very, very, very, very good price

I just called Apexjr and ordered 32 of these. This will give me 240000uF per channel, should be enough.
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