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Old 3rd April 2013, 06:42 PM   #1
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Default Luxman L11 service manual wanted

Hi, ....anyone who has the Luxman L11 service manual, or knows the correct bias settings for the L11 poweramp?

For the moment the 2SA1075 / 2SC2525 gets 25mA each, but I am not sure whether this is within the L11 specifications.

A copy of the L11 service manual would be highly appreciated

L11 repair : https://picasaweb.google.com/vbkolsen/LuxmanL1102#

Thanks in advance.

Kim
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Old 3rd April 2013, 07:01 PM   #2
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For an emitter follower type stage with 0.22 ohm resistors I would have thought a shade over 100ma per pair was nearer the mark but that is a world away from 25ma so maybe thermal constraints such as heatsink size are a limiting factor.

I wouldn't alter it just for the sake of it and in reality anything over even a milliamp or two causes the crossover distortion to vanish.
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Old 3rd April 2013, 07:16 PM   #3
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Originally Posted by Mooly View Post
For an emitter follower type stage with 0.22 ohm resistors I would have thought a shade over 100ma per pair was nearer the mark but that is a world away from 25ma so maybe thermal constraints such as heatsink size are a limiting factor.

I wouldn't alter it just for the sake of it and in reality anything over even a milliamp or two causes the crossover distortion to vanish.
I did try with 50 mA ..100 mA-110mA per pair but the heatsinks is not designed for that....I touched the heatsinks after 15 minutes and they were beyond what my hands could take of heat.

......and yes , I might have to carry the 20 Kg over to my friend and the scope in order to find lowest crossover distortion.....I would like to have the service manual anyway.
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Old 4th April 2013, 06:08 AM   #4
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Anything over even just 1or 2 milliamps and the crossover distortion will disappear on a scope. Try it and see It will disappear audibly too. Try a 1Khz pure sine wave at low level and listen as you turn the bias up from zero.

For that type of output stage the figure of around 100ma per pair is optimal but the amp is compromised by its heatsinking and so can not be run at that.
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Old 4th April 2013, 09:23 AM   #5
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Originally Posted by Mooly View Post
Anything over even just 1or 2 milliamps and the crossover distortion will disappear on a scope. Try it and see It will disappear audibly too. Try a 1Khz pure sine wave at low level and listen as you turn the bias up from zero.

For that type of output stage the figure of around 100ma per pair is optimal but the amp is compromised by its heatsinking and so can not be run at that.
Those 1 or 2 milliamps to reach the area where the crossover distortion disappears, I have observed once on the oscilloscope.


Regarding components and heat, I try in my diy projects to keep the temperature as low as possible ... this L11 was no exception. The damaged standard zener WZ172, 17.2 V, which was the reason for this preamplifier not to work, were replaced with two serial 12V - and 5.2 V Zeners ... lifted up from the PCB.

In almost all Japanese amplifiers around the eighties were capacitors glued to the PCB, part of the glue also sat at zenere, resistors and transistors legs which therefore could not get rid of the heat .... very bad idea to glue capacitors onto the PCB , but surely done in order to counter customer countries' restrictions..

At the same time, I reduced the heat on the two series regulators for the AF preamp with 2 small cooling fins.....the two close-up mounted capacitors likes the new cool surroundings.

The output transistors and the design of heat sinks can not be changed that much ... so the approximate 25mA per transistor fits reasonably to the heat sinks size.. I think.........but, I don't know for sure?
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Old 4th April 2013, 11:46 AM   #6
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Glue and the problems it caused were an industry wide issue where it was not unknown for it to become slightly conductive. Many TV and VCR's suffered. Hot running passive components are another issue. I've seen service bulletins that advised using high melting point solder to rework certain components (because they actually unsolder themselves in service)

I agree that running it cool is probably best although most semiconductors won't even blink at temperatures that are to hot to touch comfortably.
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Old 4th April 2013, 08:17 PM   #7
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Default Luxman L11 bias settings

Information about the correct bias for luxman L11 received.

Herr. D. Kühnhold, who has serviced Luxman products since 1970, was kind enough to send the right bias values​​.
Herr. Kühnhold has a small company which also can provide DML-01 and DML-02 "IC" modules for the various Luxman amplifiers. please see:
luxman-forever.de

50mA for each set of transistors (25mA each) as assumed. As experienced was the EQ amplifier section difficult to adjust, as it took about 20-25 minutes before transistors had thermal balance. The AF amplifier was relatively easy to adjust. There is a possibility of several modifications to the Luxman L11. Additional cooling for the series regulators to AF preamplifier and stronger zener diodes few places, will extend the life considerably more of the capacitors.

Repair of Luxman L11 on Picasa Web: https://picasaweb.google.com/vbkolsen/LuxmanL1102#

Kim
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Old 4th April 2013, 08:54 PM   #8
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Originally Posted by Leakstereo20 View Post
Information about the correct bias for luxman L11 received.
And a SCH File for Easy navigation ....

Cheers
Attached Files
File Type: pdf luxman_l-11_sch.pdf (98.0 KB, 36 views)
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Old 5th April 2013, 06:25 AM   #9
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Quote:
Originally Posted by Leakstereo20 View Post
...Information about the correct bias for luxman L11 received...

So that confirms it is biased on the low side due to thermal constraints.
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Old 5th April 2013, 11:19 AM   #10
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Originally Posted by Smiley 09 View Post
And a SCH File for Easy navigation ....

Cheers
This is the standard L11 schematic file on the web and not an very easy file to read..........Find a better one here : https://picasaweb.google.com/vbkolse...30635258773250

...or even better ........ Luxman L11 PDF file uploaded today at:
https://docs.google.com/file/d/0B7UK...RxMWdtZ3c/edit

....remember to use the magnification button at Google docs.......this is A3 size ......... a papercopy possible by 2 x A4

....for Luxman owners and admirers

Last edited by Leakstereo20; 5th April 2013 at 11:21 AM.
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