aleph bias tips

slr 5000 · 12th November 2009, 12:42 AM

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

Iain McNeill · 12th November 2009, 01:37 AM

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.

MEGA-amp · 02:10 AM

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 is...do 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.

-john

slr 5000 · 12th November 2009, 03:15 AM

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

MEGA-amp · 12th November 2009, 03:41 AM

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?

Bill Fuss · 12th November 2009, 06:46 AM

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

12th November 2009, 12:42 AM	#1
slr 5000 diyAudio Member Join Date: Oct 2007 Location: melbourne	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

12th November 2009, 02:04 AM	#3
MEGA-amp diyAudio Member Join Date: Oct 2003 Location: Newington, CT	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 is...do 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. -john Last edited by MEGA-amp; 12th November 2009 at 02:10 AM.

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12th November 2009, 01:37 AM	#2
Iain McNeill diyAudio Moderator 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.

12th November 2009, 03:15 AM	#4
slr 5000 diyAudio Member 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

12th November 2009, 03:41 AM	#5
MEGA-amp diyAudio Member Join Date: Oct 2003 Location: Newington, CT	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?

12th November 2009, 06:46 AM	#6
Bill Fuss RIP 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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