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Old 11th November 2009, 11:42 PM   #1
diyAudio Member
Join Date: Oct 2007
Location: melbourne
Default aleph bias tips

hi everyone
my first post so please be gentle

i have an aleph 5 diy that i have been running for a year or so and would like to add some extra output devices
i am going to add an extra 6 per mono block

nothing else will be changed exept for the extra devices and i am wondering if the bias will still be the same or will i have to turn it up to get the same bias through the 12 per mono block as the 6 i am currently running eg 2 amp

the pcb is mini a

thankyou for any help

cheers jason
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Old 12th November 2009, 12:37 AM   #2
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Join Date: Oct 2007
Location: Santa Cruz, California
Hi Jason,
Welcome to DIYaudio. Sounds like a nice system you have there. I'm sure you've looked around and searched already but there's a wealth of information for you here.
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Old 12th November 2009, 01:04 AM   #3
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All else being equal, simply by adding more devices and corresponding source/gate resistors you will double the bias in this case. As long as you have enough heatsink, you're fine. The only other question you have enough power supply? A single large trafo can usually handle both channels Aleph5, but with 8A total, you'll need to go dual mono...if you haven't already.


Last edited by MEGA_amp; 12th November 2009 at 01:10 AM.
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Old 12th November 2009, 02:15 AM   #4
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Join Date: Oct 2007
Location: melbourne
hi to john and ian

thankyou for your advice
power supply and heatsink is oversized so no problem there

i was just wondering about the bias changing but it sounds like it will be fine
i worried that by adding extra out put devices and not changing any thing else that the bias would be lowered and i will have to up the bias to bring it back to its previous value

cheers jason
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Old 12th November 2009, 02:41 AM   #5
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You are effectively lowering the current and dissipation through each output device, but as a whole bias will be increased. What is your current power supply setup?
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Old 12th November 2009, 05:46 AM   #6
Join Date: Oct 2005
Location: Central Florida
The Aleph current source only monitors the current through one fet and supplies the bias voltage to all the current source fets. Likewise for the signal fets, they all see the same bias voltage. If you double the number of output fets you also double the total bias current unless you raise the value of the source Rs. 600va trafo for each channel probably about minimum.

Best, Bill
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