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Old 26th January 2006, 07:27 PM   #1
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Lightbulb Newbie Aleph-X Building

My proposed setting

i use 225va transformer per channel

DC Voltage Input: 26V
Rail Voltage: 20V
BIAS Current 8A
number of mos: 8 per channel

And i have enquiry on the PSU as well

does it connect like this

PSU - AC-DC Bridge - 10000uf X 2 - main board

Thank you everybody!

Angus
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Old 26th January 2006, 08:05 PM   #2
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Location: Victoria, BC, Canada
lscangus, welcome to the club!

For the DC Voltage Rails, do you mean a +20V positive rail and a -20V negative rail, or do you mean 26V from positive to negative (i.e. +10V and -10V). That will help us to give you proper advise.

In the meantime, for the settings you are quoting, a 225VA transformer will definitely be too small, and 8 output Fets per channel will also be too few.

In my Aleph-X I run the Fet's harder than most people are comfortable, and I also made the mistake of undersing my transformer. The settings for my Aleph-X are:

Transformer Rating: 225VA (one per channel)
Transformer Secondaries: 2 x 12V
Supply Rails: +15V / -15V (after CLC filter)
Bias Current: 5A
Number of Fets / channel: 4

My transformer produces a mechanical hum that is audible if there is no music playing. I have been considering relpacing the trafo's with a 300VA to eliminate this.

For your settings, I'd suggest a 600VA transformer as a minimum (assuming that you mean +20 and -20V rails), and I'd also recommend increasing the number of Fets to 12 unless you are planning on using forced air cooling (i.e. a fan).

Hope this helps give you some perspective.

Cheer, Terry
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Old 26th January 2006, 08:14 PM   #3
steenoe is offline steenoe  Denmark
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Quote:
I have been considering replacing the trafo's with a 300VA to eliminate this.
Terry, if you consider replacement for those trafos, I think you should use at least 500VA's. I dont think that the extra 75VA will make a lot of difference Maybe its just me, being overkill all the time??


Steen
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Old 27th January 2006, 08:16 AM   #4
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Thanks for all you advice

You know there is a voltage suppliy to the main board. If i use a 500va, the minium output voltage of the transformer is 25 volt, which mean after the AC-DC and the capacitor, the votage will be about 36V. +36-0- -36.

I wonder if this voltage will be too high? and also, does the rail need +20-0- -20, becasue i think the rial is the output fets voltage.

Sorry for so many question...


And last, can i parallel tow tranformer to increase the overall output?

Angus
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Old 27th January 2006, 08:32 AM   #5
steenoe is offline steenoe  Denmark
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Quote:
I wonder if this voltage will be too high?
Hi Angus. Yes, the 36 volt rails you mention is too high. The standard Aleph-X uses +/-15V rails with 2x12V trafo's, just like Terry's. A highpower version (say 100 watts) uses +/-22V rails from 2x18V trafo's.

Steen
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Old 27th January 2006, 08:36 AM   #6
steenoe is offline steenoe  Denmark
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You can pretty much calculate the A-X needs in this nice spreadsheet made by wuffwaff

Steen

NEWER Aleph-X calculationsheet AXE-1.2
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Old 27th January 2006, 08:40 AM   #7
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Quote:
Originally posted by steenoe
You can pretty much calculate the A-X needs in this nice spreadsheet made by wuffwaff

Steen

NEWER Aleph-X calculationsheet AXE-1.2

because there are two voltage. one is the supplied voltage to the board, one is supplyied voltage to the fets. What value would you recommand?

and can i parallel tranformer?

but 15V / 0.69 is 21V, will 21V be alright?
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Old 27th January 2006, 10:30 AM   #8
steenoe is offline steenoe  Denmark
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Quote:
because there are two voltage. one is the supplied voltage to the board, one is supplyied voltage to the fets
There is only one voltage, namely the one supplied to the mainboard. The Fets are "powered" directly from the mainboard. Assuming you are building a standard Aleph-X you need to feed the mainboard with +/-15V and nothing else
I hope I understood your question correctly.

Steen
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Old 27th January 2006, 10:53 AM   #9
Netlist is offline Netlist  Belgium
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Here's an example of how i did it. There is only one voltage for the AlephX as Steen explained.
I think you are confused by cell B11 and B12 in the spreadsheet.
B11 is equal to B12 if you don't use CRC or CLC. (Capacitor - resistor - capacitor or capacitor - coil - capacitor).
The final voltage at the fets is important and every R or L in the supply line will lower that voltage. Plan accordingly.

/Hugo
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Old 27th January 2006, 01:21 PM   #10
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My Aleph-X compact PCB

i am planning to buy this...

what i want is a amp which does abotu 80W output per channel. SO i think 21 V input will be fine..

but ghow abvout the bias current?
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