transformer voltage needed for Aleph 4 or Aleph 2 - diyAudio
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Old 26th November 2001, 03:17 PM   #1
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I was wondering what transformer output voltage would be suitable to create the +/- 48 volts needed on an Aleph 4 or the +/- 45 volts for an Aleph 2. Would a transformer with dual 30 volt secondaries with 4 37.5 volt taps work? Thanks for the advise.

Rob
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Old 26th November 2001, 03:36 PM   #2
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Rob,
The formula is 1.414*AC=rail for a capacitor input filter. The one caveat here is that you'll have to add a volt or two for diode losses in the rectifier. So for a 45V rail, you're looking at roughly a 33-0-33V secondary. For a 48V rail, about 35-0-35V.
Note that the voltage need not be exactly 45V or 48V. The cicuit will be perfectly happy with anything within shouting distance of that range. Just be sure that you've got adequate heatsinking if you choose to run the circuit a bit hot.

Grey
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Old 26th November 2001, 06:01 PM   #3
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Thanks so much for the input. By the way, what does it mean to say that the transformer has 30 volt secondaries, but 37.5 volt taps? I thought secondaries and taps would be the same thing.

Rob
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Old 26th November 2001, 06:21 PM   #4
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Grey the equation you provided is that for a single secondary or a dual secondary or does it even matter? So if I would use the transformer with the dual 30 volt secondaries would I get 42 volt rails before subtracting the volt or two for diodes in the rectifier? How will this affect the amps output power, and approximately to what degree? Thanks.

Rob
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Old 26th November 2001, 06:25 PM   #5
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I think I was miss reading and looking at secondaries and taps for two different transformers. Sorry about that.
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Old 26th November 2001, 07:14 PM   #6
jduncan is offline jduncan  United States
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The engineer at plitron was trying to tell me that I needed a different set for that...I'm building an Aleph 4 and want roughly 48V rails but he said that to get that I should use the one with dual 27V secondaries ....he said this would give me what I wanted....

I however, initially thought that I needed 35V secondaries too....

Could you please confirm that I really do need 35V instead of 27V?
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Old 26th November 2001, 10:47 PM   #7
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The 1.414*AC is per rail, i.e. a 30-0-30VAC transformer would give 42.42-0-42.42VDC, not including diode losses, capacitor leakage, and a bit of resistive loss here and there. The actual rail would work out about 40-41V or so.
Please note that a sufficient current draw will pull the rail down even further, but if you keep it reasonable (50-60% of the VA rating of the transformer or less), the rail will actually end up pretty close to the calculations. Don't sweat a half volt difference. We're also assuming a fair sized bank of caps. Try to save money on the caps, and the rail will collapse sooner, not to mention ripple problems.

Grey
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Old 26th November 2001, 11:14 PM   #8
jduncan is offline jduncan  United States
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OK great, so for my Aleph 4's I have a 1000VA transformer with dual 35V secondaries and a capacitor bank of .2F (6 * 33,000uF) ....this should be great right?
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Old 26th November 2001, 11:20 PM   #9
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right! The engineer at plitron has taken you for a ride..or.... he's assuming that you're building an aleph 5?
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Old 26th November 2001, 11:28 PM   #10
jduncan is offline jduncan  United States
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nah, i even sent him the schematic!
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