Luxman B12 bias setting

kro5998 · 14th August 2006, 09:53 PM

Hi, I recently got a pair of Luxman B12 mono amps on Ebay.
I restored them with new electrolytes,input and output terminals,control lights,output relays and fresh heatsink compound on all the power trannies.

They function perfectly with about 4mV of offset at the output.
The only difference between the two is the bias current.One has 115mA and the other 200mA.
Neither get very hot in iddle.

Does anybody know the correct bias setting for these amps?

Any suggestion are welcome.

kro5998.

anatech · 14th August 2006, 11:05 PM

Hi kro5998,
Cool! I've never heard of those ones. Got a picture?

Anyone have a diagram for this??

-Chris

kro5998 · 15th August 2006, 06:03 PM

Hi Chris.
They look just the same as the M12 amp from the outside.The only difference is at the back.(the M12 is stereo 2 x 85 Watt)

They are rated at 150 Watt into 8 ohm but i measured 176 Watt with 0.70 Volt.

I you don't know the M12 either i'll post some pictures.

kro5998

anatech · 15th August 2006, 06:10 PM

Hi kro5998,
Okay, that I know. The bias current is measured by pulling off the gray wire on lug #2 and using an ammeter. The target was 60mA (+10, - 0 mA), or 60~70 mA. This model had two pair of outputs, so that would be 30~35 mA per device (0R18 emitter resistors).

I don't know how close that is to yours. I hope this helps.

-Chris

kro5998 · 15th August 2006, 06:38 PM

Hi Chris. Although they look similar on the outside they are not the same inside.

The endstage of the M12 runs on 48-52 Volts (driver stage 58 V) and uses two pairs of 2SD551/2SB681

The endstage of the B12 runs on 76 Volts (driver stage 95 V) and uses three pairs of 2SD665/2SB645

The emitter resistors are 0R18 ohm.

kro5998

anatech · 15th August 2006, 06:42 PM

Hi kro5998,
Okay, however the bias current per device may be the same. I'll assume the heatsink for the B12 is larger than the M12.

What was the bias measured at? If it was close to the figure (30~35mA per device) you are probably safe to trim it to those values.

-Chris

kro5998 · 15th August 2006, 06:43 PM

Chris, i can e-mail you the schematic if you want, it's too big to attach here.

kro5998

kro5998 · 15th August 2006, 06:48 PM

Chris, the heatsinks are the same size on both amps (for a class AB amp the're big).

One amp was set at 115 mA and the other at 200mA. Neither did warm up much though. Only a few deg above room temp.

kro5998

jacco vermeulen · 15th August 2006, 10:09 PM

http://luxman.fotopic.net

Hilberink added the B12 schematic, same Hilberink who hates GCs.

anatech · 15th August 2006, 11:54 PM

Hi kro5998,
That would be handy, and thank you. The link Jacco kindly provided is a type of look but don't download kind.

Please send it to bhomester at gmail dot com. You can send a very high resolution file to that one.

Looking at your numbers, 115 mA is 10 mA higher than 35 mA per device. So that is close. I don't see any value in running the outputs higher than that at idle. 40mA per device would run at 120 mA. I think your 200 mA channel might be running a little warm. Mosfet it isn't!

-Chris

14th August 2006, 09:53 PM	#1
kro5998 diyAudio Member Join Date: Dec 2004 Location: Tilburg	Luxman B12 bias setting Hi, I recently got a pair of Luxman B12 mono amps on Ebay. I restored them with new electrolytes,input and output terminals,control lights,output relays and fresh heatsink compound on all the power trannies. They function perfectly with about 4mV of offset at the output. The only difference between the two is the bias current.One has 115mA and the other 200mA. Neither get very hot in iddle. Does anybody know the correct bias setting for these amps? Any suggestion are welcome. kro5998.

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14th August 2006, 11:05 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kro5998, Cool! I've never heard of those ones. Got a picture? Anyone have a diagram for this?? -Chris

15th August 2006, 06:03 PM	#3
kro5998 diyAudio Member Join Date: Dec 2004 Location: Tilburg	Hi Chris. They look just the same as the M12 amp from the outside.The only difference is at the back.(the M12 is stereo 2 x 85 Watt) They are rated at 150 Watt into 8 ohm but i measured 176 Watt with 0.70 Volt. I you don't know the M12 either i'll post some pictures. kro5998

15th August 2006, 06:10 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kro5998, Okay, that I know. The bias current is measured by pulling off the gray wire on lug #2 and using an ammeter. The target was 60mA (+10, - 0 mA), or 60~70 mA. This model had two pair of outputs, so that would be 30~35 mA per device (0R18 emitter resistors). I don't know how close that is to yours. I hope this helps. -Chris

15th August 2006, 06:38 PM	#5
kro5998 diyAudio Member Join Date: Dec 2004 Location: Tilburg	Hi Chris. Although they look similar on the outside they are not the same inside. The endstage of the M12 runs on 48-52 Volts (driver stage 58 V) and uses two pairs of 2SD551/2SB681 The endstage of the B12 runs on 76 Volts (driver stage 95 V) and uses three pairs of 2SD665/2SB645 The emitter resistors are 0R18 ohm. kro5998

15th August 2006, 06:42 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kro5998, Okay, however the bias current per device may be the same. I'll assume the heatsink for the B12 is larger than the M12. What was the bias measured at? If it was close to the figure (30~35mA per device) you are probably safe to trim it to those values. -Chris

15th August 2006, 06:43 PM	#7
kro5998 diyAudio Member Join Date: Dec 2004 Location: Tilburg	Chris, i can e-mail you the schematic if you want, it's too big to attach here. kro5998

15th August 2006, 06:48 PM	#8
kro5998 diyAudio Member Join Date: Dec 2004 Location: Tilburg	Chris, the heatsinks are the same size on both amps (for a class AB amp the're big). One amp was set at 115 mA and the other at 200mA. Neither did warm up much though. Only a few deg above room temp. kro5998

15th August 2006, 10:09 PM	#9
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	http://luxman.fotopic.net Hilberink added the B12 schematic, same Hilberink who hates GCs.

15th August 2006, 11:54 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi kro5998, That would be handy, and thank you. The link Jacco kindly provided is a type of look but don't download kind. Please send it to bhomester at gmail dot com. You can send a very high resolution file to that one. Looking at your numbers, 115 mA is 10 mA higher than 35 mA per device. So that is close. I don't see any value in running the outputs higher than that at idle. 40mA per device would run at 120 mA. I think your 200 mA channel might be running a little warm. Mosfet it isn't! -Chris

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