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14th February 2006, 09:39 PM  #1 
diyAudio Member
Join Date: Oct 2005

AlephX Building ( Comments Needed )
Hello, thank you for you all helping me on building my first Aleph
Here is my planned Aleph configuration ( per channel ) Transformer Output Voltage : 12V Transformer Rating: 500VA PS Capacitance : 47000uF X 4 Rail Voltage : 17V BIAS : 8A Number of Fets : 8 ( IRFP044 ) BIAS Current per FETS : 1A FET's resistor value : 0.5 Ohm I wonder if this will work? i am using a active heatsink, and also, is there any thing i need to concern and take care or aware of? and also, is there any vlaue of the resistor i need to calculate? What do i have to do if i first start up the Aleph and how cna i tune the BIAS current? and how cna i measure it? Thank you very much for your help Angus 
14th February 2006, 09:59 PM  #2 
diyAudio Member
Join Date: Jun 2004
Location: Bern

Hi Angus,
if you're using 8 FETS per channel at a bias current of 8A, the current in each MOSFET will be 4 A, not 1. In an AlephX, the bias current is considered PER SIDE, that is, 8A per side. In each side, the same current flows in the upper and lower group of FETS, so you have 8A divided by the number of FETS in a group (2 in your case). Transformer: you need to have a dual supply, that is, two secondaries 12 V each, to give you a positive and a negative rail. BTW, taking into account the losses across the rectifiers, I doubt you will achieve 17V rail with 12 V secondaries. 500VA are not enough for your bias current, you should up the transformer to at least 700800 VA, to make sure it won't overheat. Cheers, Bruno 
14th February 2006, 10:04 PM  #3  
diyAudio Member
Join Date: Oct 2005

Quote:
Thank you so much, here is my new information, but in the spread sheet, i have calculated that it will produce 300W of heat, and i am using 500W transformer, why will it not enough? and also, in the WIKI tutorial, it talked about the source resistor, is it the R1 and R3 of your FETS board? and also, except those two resistor value, is there any value i need to customise for my amp? finally, is there any jumper i need to make on the main board? I am sorry for so many questions Transformer Output Voltage : 12V X 2 Transformer Rating: 500VA PS Capacitance : 47000uF X 4 Rail Voltage : 16V17V BIAS : 8A Number of Fets : 8 ( IRFP044 ) BIAS Current per FETS : 4A FET's resistor value : 0.125 Ohm 

14th February 2006, 10:16 PM  #4 
diyAudio Member
Join Date: Jun 2004
Location: Bern

OK, let's see...
I assume the spreadsheet you mention is the "AXE12.xls", right? In this case, the bias current is the total one for the channel, that is, 4A per side. Your numbers then make sense, just the source resistors are off, they must be 0.25 Ohm (they' re R2 and R4 on the driver board). I would still get a bigger transformer, as the voltage under load could drop considerably with a smaller one; moreover, the transformer could get quite ... Cheers, Bruno 
14th February 2006, 10:39 PM  #5  
diyAudio Member
Join Date: Oct 2005

Quote:
So what is the Value of R1, and R3? and also in the diagram you have provided it said it is 208.. anyway.. and also... how about the answers of the rest of my questions? are they okay? 

16th February 2006, 09:41 AM  #6 
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Join Date: Oct 2005

so what is the value of R1 and R3? if i use 4A per side?
Angus 
17th February 2006, 10:49 PM  #7  
diyAudio Member
Join Date: Jun 2004
Location: Bern

Quote:
Quote:
R1 and R3 are gate stopper resistors, their value is 220 ohms and is not critical (see also this link ). The only resistors you have to customise are R2 and R4, that is the MOSFETs source resistors. And no, on the mainboard there's no jumpers to be made. Cheers, Bruno 

20th February 2006, 01:07 PM  #8  
diyAudio Member
Join Date: Oct 2005

Quote:
so if i use a total bias of 8A per chanel ( BIAS current in Spreadsheet ), and i will use 8 fets per channel, what will the value of R2 and R4 be? Angus 

20th February 2006, 01:20 PM  #9  
diyAudio Member
Join Date: Jun 2004
Location: Bern

Quote:


21st February 2006, 08:17 AM  #10 
diyAudio Member
Join Date: Oct 2005

ops.. sorry i missed that. so if i use a 500va transformer, will it be okay?

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