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Old 5th August 2012, 10:49 AM   #11
diyAudio Member
Join Date: Nov 2011
Default help for bias setting


excuse me if it was asked before . I have some problem with my newly built av400 amp.i don't know how to set to multiturn potentiometer to access the best sound quality and avoid produce excessive heat on IRFPs.
I wonder if it's possible for you to help me how can i set it practically .
I was reading the instruction written by Mr holton but i didn't get the point.
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Old 5th August 2012, 04:54 PM   #12
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Join Date: Feb 2010
measure the voltage across your 1ohm source resistors, adjust pot for your required current.
i would suggest 10mV as a starting point, check all devices at this level, they should be 9-11mV if matched sufficiently.
When you have finished build, then try adjusting to suit your taste, heatsink etc. many threads already on this topic.
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Old 5th August 2012, 05:08 PM   #13
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if you mention the 5-watt resistor of source pin of each MOSFET, it should be noticed that they're 0.22 ohm not 1 ohm. now do i make a mistake or you mention something else?
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Old 5th August 2012, 05:53 PM   #14
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Join Date: Nov 2011
fortunately I got the point .

but my resistor voltages are varied. i set the highest voltage on 18mv but the others are 9mv and 10 mv and even 3 mv . how can i match the MOSFETs together. and what happend if they still unmatched?

thank you for helping me.
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Old 6th August 2012, 08:29 AM   #15
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i've read the instruction for matching the MOSFETs but do i need more than 4pair of IRFPS to have the closest match or not?
could anyone explain how to match them?
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Old 2nd February 2013, 02:11 AM   #16
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Join Date: Feb 2013
PCB AV400 R1 ؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟ ؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟؟

Last edited by ebix11111; 2nd February 2013 at 02:31 AM.
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