Luxman L58A / 2SK163-2SJ44? - Page 3 - diyAudio
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Old 13th August 2010, 09:07 AM   #21
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Quote:
Originally Posted by jechentau View Post
no, i do not have such amp (so offtopic perhaps), however as i peered over the schematic i noticed those double series diodes as reference for the vartious ccs'es (or so it appears to me) and i already wondered of this 2v8 zener i have (unrelated to such amp) is just 4x0,7V forward junctions in series (say 4x 1n4148 in a black thinlead ge-diode glass casing) however i am sure it is a silicon device, because it is a "B" device (silicon).
what is the voltage of the reference diodes in the luxman amp btw?
- Can't find any voltage messurements on the scanned L58A manual page, and I have only repaired the regulated psu for the driver board, resoldered most of the power board - and the L58A sounds just nice. I don't want to change the used components in L58A from around 1982 , nor the original design made by Luxman.

The question no. one is whether it is possible to find substitutes for 2SK163-2SJ44? I think the silke soft highrange reproduction is generated by the inputfets??

Like Mr. Wahab and my friend pointed out, the design of the L58A power stage is good!

The question to you engineers:

"Is it possible to make some minor changes in the L58A input stage design in a way that we keep the sonic sound quality , and at the same time adds a little more drive power to the output stage( 2 pairs of 2SJ50/2SK135 respectively 2SJ162/2SK1058)?"

I might have a burned out M150 for that experiment!

rgds
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Old 13th August 2010, 09:26 AM   #22
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Originally Posted by wahab View Post
The L58 has some drawbacks...
first, the power amp stage has a very high gain
of about 120..I suppose that it allow for preamp
circuits to work with low gain and reduce distorsion
of these first stages, but then, the power stage
lose some available feedback to reduce THD..

Second, the power mosfets drivers work at low current,
typically about 3 mA , wich is not enough...

Third, it seems that the cascoded differential stage work
with a relatively high current , so the bjt cascodes have
to dissipate something like 250mW each, wich is too much
for the 2SA872/2SC1775 ....

All in all, it s a pity, since the general design ideas are
fairly good but the practical implementation is not up
to these ambitions...
- Seems as if you have experience with similar designs like the L58A? The power mosfet drivers may work by too low current, but I can assure you that the power mosfet gets fairly hot within one hour of drive.

Like I asked above: Is it possible to make some changes in order to optimize the L58A driver - and power stage design?

If this change of the L58A design becomes too complicated, I will have to stay with the M100 design , from 1982 with the BF760/BF757 drivers - not quite as good as the L58A in sound reproduction, but still better than many amplifiers with bipolar power stage.

rgds.
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Old 13th August 2010, 09:47 PM   #23
wahab is offline wahab  Algeria
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If the amp work well, it s perhaps better to leave it as it is.
Modding such a beast is not that easy and requires a good
lab equipement to ensure that the amp retain its stability.
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Old 13th August 2010, 09:57 PM   #24
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Quote:
Originally Posted by wahab View Post
If the amp work well, it s perhaps better to leave it as it is.
Modding such a beast is not that easy and requires a good
lab equipement to ensure that the amp retain its stability.
Yes - I have seen that small "tags" on the square sinus on scope could create unstabilty higher up in frequence. I shall stay with the old circuit.
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Old 5th October 2010, 03:22 PM   #25
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Quote:
Originally Posted by KJ2005 View Post
I have just bought a very nice Luxman L58A still working - But , the circuit for the amplifier part showed, that Luxman for the input differential stage has used 2SK163 and 2SJ44 from NEC.

It is possible to buy the 2SK163 in Europe but impossible to find the complementary 2SJ44.

Does anyone know if there is a substitute pair of fet's available with the approx. same spec's?

Have just bought the output fet's - the original were 134/49 but the 2Sk135/2SJ50 bought takes 160V instead of the original 140V.

Any help would be appreciated.

Rgds.
Kim Hansen
Denmark
Europe

Please find some vintage Luxman amps at: TUBEAMP and find the link to "Skysite"!
2SK163/2SJ44 datasheets now available from RENESAS:
http://www2.renesas.com/maps_download/pdf/TC-5409.pdf
http://www2.renesas.com/maps_download/pdf/TC-5466.pdf
http://www2.renesas.com/maps_downloa...itcode=TC-5466
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Old 5th October 2010, 03:52 PM   #26
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Hi tiefbassuebertr ,

Thank you very much for the 2SK163/2SJ44 datasheets.

While I am making a "non feedback" DC amplifier with bipolar transistors just now , I am still thinking of my mosfet project for which I have bought 20 pcs. of the 2SJ50/2SK135 original Hitachi output fets. I don't want to change my L58, Luxman, but I would very much like to built a input stage with the mentioned 163/44 fets. Unfortunately NEC don't make them any more.

Do you have any suggestions? - or somewhere to find a new old stock?

Kind regards
Kim H.
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Old 5th October 2010, 05:51 PM   #27
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Quote:
Originally Posted by KJ2005 View Post
Hi tiefbassuebertr ,

Thank you very much for the 2SK163/2SJ44 datasheets.

While I am making a "non feedback" DC amplifier with bipolar transistors just now , I am still thinking of my mosfet project for which I have bought 20 pcs. of the 2SJ50/2SK135 original Hitachi output fets. I don't want to change my L58, Luxman, but I would very much like to built a input stage with the mentioned 163/44 fets. Unfortunately NEC don't make them any more.

Do you have any suggestions? - or somewhere to find a new old stock?

Kind regards
Kim H.
I am not sure, what means "non feedback DC amplifier". I real life such amps don't exist.
Mean you perhaps an amplifier without NFB (negative feed back/global feedback)?
Other variations are
- an amplifier with global feedback only inside of two voltage gain stages (front end resp. diff amp + VAS stage), i. e. the power buffer push pull stage is outside of this loop.
- an amplifier with global feedback only inside of one voltage gain stages (i. e. without diff-amp or folded cascode or diff-amp with unity gain).

Please send me your simplefied schematic to know exactly, what for you is a "non feedback DC amplifier" and let me know your wanted idle current through the output stage (classA or A/B).

Better available for old NEC replacement are various types from Toshiba:
Junction FETs (Single) | MOSFETs | TOSHIBA Semiconductor Company
and RENESAS
http://www2.renesas.com/discrete/en/.../lownoise.html
http://www2.renesas.com/discrete/en/...t/general.html
http://www2.renesas.com/discrete/en/..._lownoise.html
http://www2.renesas.com/discrete/en/...spice_2sj.html (Spice Models)

Last edited by tiefbassuebertr; 5th October 2010 at 06:01 PM.
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Old 5th October 2010, 06:01 PM   #28
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My friend John Wright at Museatex just got an L58A and plans to refurbish it shortly. You might contact him as he does design work. The Museatex amplifiers in the STR and MTR range all use the same Diamond buffer front end design as used in the Luxman. John modifies the Meitner amps with a cascode second stage as in the Luxman L58A. You can contact John via the Museatex web page. Regards Moray James.

:: museatex ::
__________________
moray james
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Old 5th October 2010, 07:49 PM   #29
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Quote:
Originally Posted by tiefbassuebertr View Post
I am not sure, what means "non feedback DC amplifier". I real life such amps don't exist.
Mean you perhaps an amplifier without NFB (negative feed back/global feedback)?
Other variations are
- an amplifier with global feedback only inside of two voltage gain stages (front end resp. diff amp + VAS stage), i. e. the power buffer push pull stage is outside of this loop.
- an amplifier with global feedback only inside of one voltage gain stages (i. e. without diff-amp or folded cascode or diff-amp with unity gain).

Please send me your simplefied schematic to know exactly, what for you is a "non feedback DC amplifier" and let me know your wanted idle current through the output stage (classA or A/B).

Better available for old NEC replacement are various types from Toshiba:
Junction FETs (Single) | MOSFETs | TOSHIBA Semiconductor Company
and RENESAS
Low noise | J-FET | Transistors | Discrete | Products | Renesas Electronics
For general use (general purpose) | J-FET | Transistors | Discrete | Products | Renesas Electronics
High sensitivity and low noise | J-FET | Transistors | Discrete | Products | Renesas Electronics
2SJ Series | SPICE Models | Discrete | Products | Renesas Electronics (Spice Models)
Might give you an answer later - need to ask for any copyright.
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Old 5th October 2010, 07:52 PM   #30
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Quote:
Originally Posted by moray james View Post
My friend John Wright at Museatex just got an L58A and plans to refurbish it shortly. You might contact him as he does design work. The Museatex amplifiers in the STR and MTR range all use the same Diamond buffer front end design as used in the Luxman. John modifies the Meitner amps with a cascode second stage as in the Luxman L58A. You can contact John via the Museatex web page. Regards Moray James.

:: museatex ::
Thank you - I shall ask him later.

Rgds
Kim
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