Luxman L11 service manual wanted

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Mooly

Mooly

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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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Leakstereo20

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Mooly said:
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.
Click to expand...

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.
 
Mooly

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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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Leakstereo20

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Mooly said:
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.
Click to expand...

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?
 
Mooly

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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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Leakstereo20

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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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Leakstereo20

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Smiley 09 said:
And a SCH File for Easy navigation ....

Cheers
Click to expand...

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/vbkolsen/LuxmanL1102#5862330635258773250

...or even better ........ Luxman L11 PDF file uploaded today at:
https://docs.google.com/file/d/0B7UKVCxCGsm2Y2FPa2RxMWdtZ3c/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:)
 
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Leakstereo20

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Mooly said:
So that confirms it is biased on the low side due to thermal constraints.
Click to expand...


Well .... Currently we can't really say anything about thermal limits, before we know whether Luxman engineers designed the heat sinks to be accurate enough for this AB output stage.
It could be that exactly 25mA per. transistor is the number of milliamperes which removes or eliminates the crossover distortion? ... or at least the majority of the crossover distortion.
.....we need to measure the output stage!:)
 
Mooly

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25ma will certainly eliminate most of the distortion.

Have a read at the work done by Doug Self in his "Audio Power Amplifier Design Handbook" which covers biasing in great detail. The critical parameter is actually the volt drop across the two emitter resistors combined and would be around 0.05 volts for an emitter follower output stage such as this. That equates to a current of around 114 milliamps per pair.
 
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Leakstereo20

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Mooly said:
25ma will certainly eliminate most of the distortion.

Have a read at the work done by Doug Self in his "Audio Power Amplifier Design Handbook" which covers biasing in great detail. The critical parameter is actually the volt drop across the two emitter resistors combined and would be around 0.05 volts for an emitter follower output stage such as this. That equates to a current of around 114 milliamps per pair.
Click to expand...

57 milliamps per transistor can 2SA1075 and 2SC2525 not handle clamped on this heatsink in L11....for sure! ....and the mentioned OP's are discontinued, so we have to take care of them!:)

This large number of milliamps you mention, and even more for Class A was the cause of the models L530 and L550 often had to be repaired on the workshop table.
Was there low to "the ceiling" where the amplifiers were located the output transistors gave up quickly. This was the reason why the local supplier reduced bias for these Class A amplifiers (incidentally without giving information about the operation)....
The mentioned amplifiers could not breathe enough .....but the musical sound from the Luxman Class A amplifiers were top class:)
 
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