Luxman L550X RESTORATION: Advise regarding OP amps :

quadklipsh

quadklipsh

Super Member
hello guys ....

After a long two months or so My Luxman has been fully recapped and tested for hours and is sounding absolutely sublime now . While i discussed a few things about it the tech suggested that i get the OP amps changed for better quality ones .
"What difference would it bring? " was my usual query ,and he started stating the differences between consumer grade components used in the tape decks and the aerospace or medical grade components used in the those machines .

I am convinced but would like the experts to suggest me here on AK .regarding op amps .
what new op amps are the original ones to be replaced with and why ???

thanks .
 
Those J-fets on the picture 2sk146V, are some of the best produced! They are almost uobtanium. Many newer high end audio circuits have some of the same layout in the driver/input - stage..

In my 2 Luxman M-05, the same J-fets are used in the driver stage, and the sound is really high end!!
 
yes they are working fine ,as the amp was quite holding its own against a supreme 600 , which is to say the luxman is sounding pretty darn GOOD.
Ok ill confirm with my tech friend and see if the op amps are these or is there a confusion on my part
 
Could not find the L-550x sm. Looking at the L-550 it uses NJM4558 in what looks like fet gate control circuitry.
Luxmans always give me a headache. NJM4580 is an upgraded version of the 4558, however there are better
again. In the L-550, don't appear to be audio path, more control, so it's doubtful you will get any sonic improvement
if the 550x is the same.

As previously suggested, best to benchmark your unit against another/similar L's. I'd only tinker with it if it's
lacking, assuming its been recapped.

The opamps are integrated circuits, basically a circuit encased in a slab of black platic, 8 legs like
pins.JPG
 
hmmm. thanks alot for the info. ill see what my tech has in mind. if the luxman sounds a bit.more trebly maybe thats a function of t sonic signature .
Do the op amps impart a change in that????
 
In some designs, the preamp and/or phono stage consists almost entirely of opamps. This is generally seen as a cost
saving measure despite the impressive spec's of some opamps. It is in those designs where "opamp rolling" may produce
a benefit. In those designs the sonics are certainly affected. Opamp rolling should be done with some care/consideration and
careful analysis of datasheets. Surrounding components may also need to be changed.

For the L-550 (not your 550x), the preamp appears to be mostly traditional(?) discrete components. The opamp appears to
be used in a feedback role to control a FET gate voltage. I would like to add again that my knowledge of luxman circuitry is
poor and I'm sure your tech is more knowledgeable. However, since the L-550 (and probably L-550x) preamp is discrete rather than opamp based it is doubtful you will get any sonic change/improvement from opamp rolling.
 
I have been listening to this newly recapped luxman and it sounds great already. it has a gentler sound. especially in the bass. and it is very well controlled. Even so that it sounds better than the Kenwood supreme 600 also in bass responce ...
However the supreme doesnot make use of (ICs) OP amps . and the musicality is more pronounced in that one.
Comparing to Sansui 9500 , I prefer the mid bass and midrangy sound of the 9500 which is pretty kool .
but that doesnot mean it lets down the luxman down in anyway. the luxman has its own way .its a very refined and clear sound. and im loving it. That power of 50 watts feels like 150 .

id like to know if there are OPAmps that give the luxman a more midrangey sound or a more mid bass bloated sound.
or should I just use those tone controls .lolz.
 
As mentioned by mbz, there are no op amps in the signal path!

The L550 and L550X have the same circuit layout, and as mbz said, there is an dc servo/feed back!! opamp used in the duo beta circuit loop, which have no direct influence on the sound signature. There is no easy way of improving (which is quite good!!) the sound signature off this integratet amp, beside changing diodes, resistores and capacitors. And again only the ones which are sitting in the signal path.

Just use the servicemanual for L550 amp, which i almost totally identical to the 550X. The difference between the 2 models are few different parts in powersupply etc, but with the same circuit layout!

If the sound lacks control of bass or problems in midrange etc, then its most likely youre speakers which doesn't fit this amp. It's not the most current strong amp, so paired with the right speakers, it plays better than 95% of most intergratet amps!

L550_duobeta

L550_duobeta

 
Last edited:
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ok. im not fiddling . or let anyone fiddle with OP AMPs ...
so what type of speakers go best. with this amp would be a next. question . mine are a pair of audax diy speakers . 70 watts . 8ohm. 91 db.
 
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