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Old 13th October 2004, 11:18 PM   #1
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Question Aleph 1.2 under sized transformer?

I'm moving right along on building a pair of Aleph 1.2,the cases are about complete< the boards are stuffed etc.....but after continued research , I think the Plitron transformers I purchased are to small. They're 1500VA 50/50VAC, but yeaterday I read an article written by "the one and only" Mr. Pass...... "Power Supplies" @ www.passlabs.com. Nelson stated in that article that a class A amp. with 200 watts RMS would draw 1000 watts @ idle and need @ least a 3000 watt transformer. (my wording not Neisons). What should I do? Buy 2 new 3000 watt transformer or can I double up the 2-1500's and buy 2 more 1500's - would that work?

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Old 13th October 2004, 11:37 PM   #2
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Im still in the process of building my Aleph 2s (very time consuming). Ive seen many people using 1500VA for the Aleph 2, and Nelson has recommended that as well. I believe you can get by with one 1500VA for your 1.2s, but you may run a little short, I may be mistaken. My approach is overkill, which I think works well for a lot of people. I think ideally youd need 2500VA or higher. I think it would be best to buy 2 more 1500VA. But since your case is nearly complete, it may be tough to fit another one those 27lb puppies in there.
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Old 13th October 2004, 11:52 PM   #3
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Thank you MEGA-amp for the quick repely. I've got the room in the cases with one minor change, thats not a problem. So you think 2 bridges is best?

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Old 14th October 2004, 04:00 AM   #4
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If you're putting 2 1500va transformers in, yes. And I would use 3 sets of caps. Each tranformer and bridge feed 1 set, and then the 1 sets of caps feed a third set through .2 ohm or so resistors making a CRC supply of sorts.

If you're replacing with one big 3000 VA transformer, adding the second bridge just puts 2 more diodes in series and drops an extra volt.

PS the Aleph 1.2 only draws 480 W at idle. (4A @ 120V rail to rail). I think you could squeak by with 1500 VA. The Aleph current source is modulated and only idles at 1/2 current. I think he was speaking of standard current source class A. But there is nothing wrong with overkill!
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Old 14th October 2004, 10:54 AM   #5
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Hi,

keep in mind that the bigger transformers usually have more problems with (mechanical) hum and that you will need a very good softstart to turn it on.
Since they are also physically bigger the distance to the input boards will get smaller too so you´ll have to watch out for noise/hum problems.
1500VA certainly is enough for an amp idling at 500 watts.

Depending on the spec of the transformers (VA @ ambient temp) you could go as high as 750 watts. Remember it´s a class A amp so no big changes in current delivery are needed.

William
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Old 14th October 2004, 04:17 PM   #6
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Thanks guys for the good info.I wish I knew what Mr. Pass used inthe production 1.2's. I though I could parallel connect 2-1500VA or 1-1500 and 1-1000VA but that's not what I'm hearing?
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Old 14th October 2004, 04:28 PM   #7
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You can use 2 1500 VA if you want, but don't just parallel them, give them each a bridge so the one that puts out .5V more isn't trying to carry the whole load alone. The extra set of caps and resistors will further insure current sharing, But William seems to concure that the extra tranformer capacity it not needed.
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Old 14th October 2004, 10:14 PM   #8
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Steve,

If you want to spend extra money on transformers, that is up to you but I think the concensus is that 1500 VA is more than enough for one channel of an Aleph 1.2.
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Old 16th October 2004, 02:34 PM   #9
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Thanks again for the great advise so quickly.......and the concensus is I'm using the transformers I have, saving the money for my kids education. hehehehe.

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Steve
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Old 16th October 2004, 04:02 PM   #10
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Teach them the value of a good sounding set of amps...spend the money you save on some other improvement.
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