transformer voltage needed for Aleph 4 or Aleph 2 - Page 2 - diyAudio
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Old 27th November 2001, 12:09 AM   #11
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A 27-0-27VAC transformer would give you rails on the order of 36-37VDC after taking into account the diode drop, etc. The Aleph would work, but would not develop rated power.

Grey
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Old 27th November 2001, 07:53 PM   #12
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Hello,
Should 600VA also be enough?
The aleph 4 consumes 500W so 600VA should be enough I hope!
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Old 27th November 2001, 07:55 PM   #13
jduncan is offline jduncan  United States
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It actually consumes a bit more than 500W ....its closer to 570W if you have 48V rails....even though it is an SE design you should still also allow for significant headroom...I'm personally using a 1000VA toroid but you should at least use a 750VA one...they're not much more expensive than 600VA ones
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Old 27th November 2001, 08:10 PM   #14
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Hallo jduncan,
because it is an SE design you have to use an 1000W
transformer. You are drawing permanently 570W. In other
design (class AB you need only peak power). An 600W
transformergets too hot. Better to take two 600W transformer
and stack them together. You can flip one and cancelout the
scalarvector. (my next try)
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Old 27th November 2001, 08:11 PM   #15
jduncan is offline jduncan  United States
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Yeah, that's why I'm using a 1000VA transformer....sorry, I kindof ignored heat in the last post but you need it for heat reasons too
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Old 27th November 2001, 08:16 PM   #16
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So if I use a 1010VA toroid with dual secondaries of 37.5 volts multiply that times 1.414 gives me 53.025 volts subtract 2 volts for diode capacitive and resistive losses and I end up with 51 volt rails. Am I correct in thinking that this is acceptable for an Aleph 4 which specs. 48 volt rails as long as I've got enough heatsinking on the output devices. Will it signifigantly increase needed heatsinking on the other semiconductors? What about an Aleph 2 which specs 45 volt rails?

Rob
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Old 27th November 2001, 08:19 PM   #17
jduncan is offline jduncan  United States
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it's fine for either as long as you can deal with the heat.... it's not a huge increase, but it is an increase....

I'm personally using dual 35V secondaries but 37 or 38 volts is fine
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Old 27th November 2001, 11:01 PM   #18
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Rob, I believe you'll use the toroids sourced from apexjr?
Don't worry about the slight increase in the voltage. Be expected to lose a volt or two under current draw, which will leave you with less than 51V.
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Old 27th November 2001, 11:34 PM   #19
grataku is offline grataku  United States
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Guys,
don't forget that the plitron and all transformers are rated for voltage under full load. At and above 500VA this voltage drop is about 4 %. So if one uses a 1kVA transformer for the aleph 4, which draws a constant 500VA, the and the voltage drop is assumed to be linear, one would end up with (35+(35*0.02))*SQRT(2)=50.48V, again without accounting for the diode drop.
When building class AB amps I tend to be conservative in the voltage rating meaning I buy transformer with a couple of volts less than they should have. Plitron makes good transformers, with low resistance large section wires, however, I sometimes bought transformers in which thin gauge wire is used and the drop is compensated by adding a whole bunch of extra windings that bring the voltage way above what it should be. Once the problem was so severe that I had to remove windings from the transformer.

[Edited by grataku on 11-28-2001 at 01:49 PM]
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Old 27th November 2001, 11:42 PM   #20
grataku is offline grataku  United States
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Diy Student,
by the way I am building the aleph4 myself I ordered the trasformer but I don't know what to do for heatsinks, where are you buying yours? I found some but they would cost me 85$ each x 4 = too much money!!
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