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Old 20th April 2009, 02:27 PM   #1
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Question HELP! (again)

I'm at a point where I need to purchase a pair of transformers for my aleph 30 monobloc build. I'll be following the transformer with an IXYS VBE55-060N07 rectifier bridge (600V, 68 amps), filtered through three 35V, 33,000uF CE THA Panasonic caps per rail, with a .47 resistor between the second and third cap in each series. I'll be over-biasing the amp at about 2.7 amps, and adjusting the AC current gain accordingly.

Which tranny would be most likely to provide me with stable 25 V rails under power: a 300VA 18-0-18 or a 300VA 20-0-20? I can easily swap out the resistors for another value if needed.

Sorry about the question, but I can't get Duncan's PSU designer to behave in my 64 bit PC.


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Old 21st April 2009, 06:34 AM   #2
Buhl is offline Buhl  Denmark
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Well - I have not used Duncan PSU designer, but I can say that if you really want 25 volt rails (and that is not critical with A30 - a few volts up or down will not make a difference) you do not want to go with the 18 volt. 18 multiplied with Square root of 2 gives just a tad over 25 volt - Daddy Nelson normally recommends using 1.3 or even 1.2 as a multiplication factor instead of the 1.41 (sq root of 2) that we learned about in school - due to diode loss etc. Then, on top of that you want to burn voltage in a CCRC filter - which eats even more voltage.

I would go for the 20 volt - if not a 22 volt if you want to use resistors in series. And, I would also go for about the largest trannie you can fit in the chassis if you want to raise the BIAS -> big is nice - very big is very nice

Kind regards
"Calculations? We don't need no stinkin calculations! We just make them really big!" Quote: Nelson Pass
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Old 21st April 2009, 11:37 AM   #3
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Default Thanks, Hans!

That was my reasoning, too, but since I hadn't already bought a pair...

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