aleph 2 help

slr 5000 · 18th December 2009, 10:16 PM

hello to everyone

i have just finnished some kk pcb aleph 2 and have read about leaving r19 out of the circuit to raise the bias

in an aleph 2 this is the 1k is this correct ? and the 56k2 r 17 still gets installed ?

how crucial is the 56k2 value can i use 56k instead without hurting my amplifier

cheers from jason

MEGA-amp · 18th December 2009, 10:45 PM

R19 is referencing Pass Labs schematic, It's the 56.2K resistor. It trims DC bias. I just leave it out altogether, bias will generally increase by 500-600mA overall.

Nelson Pass · 19th December 2009, 04:59 AM

Yes, it's used for cases where the circuit does not have
quite as much heat sinking as you might want. You
can trim the bias down arbitrarily without screwing around
the ratios of other values.

slr 5000 · 22nd December 2009, 11:01 PM

hello fellow diy,ers

thankyou for you advice mr pass and mega

i have left r19 out and the mono blocks are running great so far
both are around .18 mv offset and the bias is .6v across the source resistors

one side of one mono block is .5v though for some reason ,how might i correct this ?
the output devices are well matched by tech diy store and the irf920 are also matched triplets so what could cause this

other than the small bias difference on one mono block they are playing great and sound magnificent
they are built as aleph 2 but run on aleph 5 voltage they run between 55 to 63 c temp depending on outside temp and are dead silent when switched on

cheers jason

Nelson Pass · 23rd December 2009, 10:51 PM

You can try trimming the resistor value coming off the Drain
of the input transistor to the - rail for that much offset.

slr 5000 · 25th December 2009, 09:54 PM

hello nelson

i am very greatfull to you for being able to build this amp ,the more i am listening to it the more it is impressing me

any hints on how much to trim that ressistor ?
a starting value perhaps

cheers jason

Nelson Pass · 26th December 2009, 03:27 AM

Try a larger a larger value. If the original is 392 and gives
you +.5V, then try 475 ohms.

slr 5000 · 26th December 2009, 08:20 AM

thankyou mr pass
i will give it a try

cheers jason

gianc · 29th December 2009, 07:27 AM

I would like to try high bias on my Aleph 5, currently I have 221K for c19 and heat sinks are not that hot. When you say to leave out r19 does that mean I can snip one side of r19 and it open, or are you supposed to jumper r19 as I have read in another post (Top ten ways to a better Aleph).

MEGA-amp · 29th December 2009, 12:07 PM

leave it open

18th December 2009, 10:16 PM	#1
slr 5000 diyAudio Member Join Date: Oct 2007 Location: melbourne	aleph 2 help hello to everyone i have just finnished some kk pcb aleph 2 and have read about leaving r19 out of the circuit to raise the bias in an aleph 2 this is the 1k is this correct ? and the 56k2 r 17 still gets installed ? how crucial is the 56k2 value can i use 56k instead without hurting my amplifier cheers from jason

29th December 2009, 07:27 AM	#9
gianc diyAudio Member Join Date: Oct 2004	Same question for Aleph 5 I would like to try high bias on my Aleph 5, currently I have 221K for c19 and heat sinks are not that hot. When you say to leave out r19 does that mean I can snip one side of r19 and it open, or are you supposed to jumper r19 as I have read in another post (Top ten ways to a better Aleph).

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18th December 2009, 10:45 PM	#2
MEGA-amp diyAudio Member Join Date: Oct 2003 Location: Newington, CT	R19 is referencing Pass Labs schematic, It's the 56.2K resistor. It trims DC bias. I just leave it out altogether, bias will generally increase by 500-600mA overall.

19th December 2009, 04:59 AM	#3
Nelson Pass The one and only Join Date: Mar 2001	Yes, it's used for cases where the circuit does not have quite as much heat sinking as you might want. You can trim the bias down arbitrarily without screwing around the ratios of other values.

22nd December 2009, 11:01 PM	#4
slr 5000 diyAudio Member Join Date: Oct 2007 Location: melbourne	hello fellow diy,ers thankyou for you advice mr pass and mega i have left r19 out and the mono blocks are running great so far both are around .18 mv offset and the bias is .6v across the source resistors one side of one mono block is .5v though for some reason ,how might i correct this ? the output devices are well matched by tech diy store and the irf920 are also matched triplets so what could cause this other than the small bias difference on one mono block they are playing great and sound magnificent they are built as aleph 2 but run on aleph 5 voltage they run between 55 to 63 c temp depending on outside temp and are dead silent when switched on cheers jason

23rd December 2009, 10:51 PM	#5
Nelson Pass The one and only Join Date: Mar 2001	You can try trimming the resistor value coming off the Drain of the input transistor to the - rail for that much offset.

25th December 2009, 09:54 PM	#6
slr 5000 diyAudio Member Join Date: Oct 2007 Location: melbourne	hello nelson i am very greatfull to you for being able to build this amp ,the more i am listening to it the more it is impressing me any hints on how much to trim that ressistor ? a starting value perhaps cheers jason

26th December 2009, 03:27 AM	#7
Nelson Pass The one and only Join Date: Mar 2001	Try a larger a larger value. If the original is 392 and gives you +.5V, then try 475 ohms.

26th December 2009, 08:20 AM	#8
slr 5000 diyAudio Member Join Date: Oct 2007 Location: melbourne	thankyou mr pass i will give it a try cheers jason

29th December 2009, 12:07 PM	#10
MEGA-amp diyAudio Member Join Date: Oct 2003 Location: Newington, CT	leave it open

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