Leestereo's Restoration/Upgrade of a Sansui AU-555A

Discussion in 'Exclusively Sansui' started by Leestereo, Mar 30, 2018.

  1. playittwice

    playittwice Well-Known Member

    Messages:
    636
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    As stated earlier, beautiful job and awesome write-up. It’s awe-inspiring and gives much motivation to re-store these fine pieces of vintage gear.

    Thanks.
     

     

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  2. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Incredible write up..... Amazing job
     
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  3. slimecity

    slimecity Super Member

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    2,701
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    Nice, great to see you solved this. I had a 6500 and after replacing all caps and some electros with poly types, and even after putting in some newer low-noise transistors, I still couldnt address this in my unit.
     
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  4. patfont

    patfont AK Subscriber Subscriber

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    Ben as usual your work sets the standard, beautiful work. And doing this myself I can see the care you take even in component installation, all board fitted and sitting pretty.

    Question: When I do 555/505's I replace all the transistors on the amp board not just if it has the UFO's-it lowers the noise floor. When I do this I need to up the bias trimmer to 2K ohm. So the 850 Ohm would not be a match for me, can't see if you replaced all your transistors from the pic?
     
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  5. Leestereo

    Leestereo Super Member

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    2,048
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    For this 555A, on the main amplifier board, only the failure-prone 2SA726 transistors (TR801/TR802) were replaced. If you implement the mod, I think that with a 2kohm trimmer installed, you can keep the stock 1.2kohm resistors.
     
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  6. patfont

    patfont AK Subscriber Subscriber

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    Yes, sounds about right, because they just miss with the 1K trimmers.
     

     

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  7. stereofun

    stereofun Super Member

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    Leestereo - your restorations will be visited for a very long time. As the next generation(s) restore these audio pieces - it is your documentation that will be considered one of the best sources :beerchug:
     
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  8. afroaudio

    afroaudio Active Member

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    157
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    Awesome documentation here Leestereo! To be referenced for years to come as stereofun said.. very keen to try the Baxandall mod, the 555A is voiced beautifully but tightening up that woolly bass will make it even better! thanks for the dedication
     
    Last edited: Jun 15, 2018
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  9. slimecity

    slimecity Super Member

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    2,701
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    Thanks Lee - your detailed write-up has inspired me to chase (and win) a 555a here in NZ on our local auction site.

    It was being worked on by a fella who subsequently died and his son is selling it. Seems to only be missing the major caps from the main board - so I can replace those, then test, then work thru and make your changes step by step.

    819437006.jpg 819437403.jpg
     
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  10. slimecity

    slimecity Super Member

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    2,701
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    Heres my take on the tone board. This, along with new Superthrough caps on the main board still give the amp that warm fuzzy sound but with a bit more detail and clarity, and a nice crispness to vocals. Very impressed and cant wait to finish these mods - especially the Baxendall diode mod.

    IMG_4421.jpg
     
  11. Leestereo

    Leestereo Super Member

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    Very nice; looking forward to seeing the rest of the restoration.
     
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  12. musichal

    musichal poet emeritus Subscriber

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    Most impressive documentation of a restoration/mod I've ever seen. I understand very little of it, but read all of it. The word meticulous comes to mind, from the quality of the work to the way it is presented. Mad skills, including the close-up imaging. Thanks for taking the time.
     
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  13. ConradH

    ConradH Addicted Member

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    Nice! I've always found efforts to improve RIAA curves pay off in SQ if you listen to those flat licorice pizza thingies.
     
  14. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I hope folk will pay attention to the fact that you didn't 'upgrade' capacitance of certain signal path caps which affect EQ response of the amp.

    'Upgrading' the wrong caps is something I am seeing more and more.
     
  15. kevzep

    kevzep Its all about the Music Subscriber

    Everything I do this sort of thing to goes straight on my FFT spectrum analyser!!
     
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  16. slimecity

    slimecity Super Member

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    Done - great writeup Lee! Im really impressed with this project. Like I say, I had a 555a (twice) before in the past but found I didnt like the sound despite doing the usual recapping etc. This time - things are different! I only had an issue with one of the caps on the back of the main amp board - I soldered it to the wrong terminal and then wondered why I had virtually no (and distorted) output on one channel. I must have been sending the pre signal straight to the chassis - after I checked all the transistors in that channel, I then realised what the issue was. Typical sansui though - seems like a fairly significant issue but no longterm damage!

    The results - the amp has lost that crispy 8-bit treble - vocals sound better than I could have ever hoped for with this amp - they have a nice clear toppy edge to them and are clear and well defined. The bass is a stunning improvement too - its focussed and punchy. I mainly listen to rock and some passages still sound a bit "slow" with this cap-coupled amp - but Lana Del Rey sounds lovely with the strings etc filling the room. Sections of the new Perfect Circle album have bass, drums and chunky guitar all slamming on the same note and I have to say this amp makes those sections sound simply incredible.

    So I also used Super throughs for the speaker coupling caps and think they could be contributing overall to the nice sound results here too.

    When I got this little amp the lid had been painted black and had some chunks out of it too - I filled them in with putty as best I could and sanded the lid back & oiled it - she came up alright I think! I did keep the original trimmers as I cleaned them with contact cleaner pretty thoroughly and they adjusted and held their values just fine too.

    Awesome!

    IMG_4456.jpg IMG_4458.jpg IMG_4459.jpg IMG_4460.jpg IMG_4461.jpg IMG_4421.jpg
     
    Last edited: Aug 1, 2018

     

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  17. Soundphile

    Soundphile Active Member

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    Every one of Lee's restoration jobs, including the wonderfully taken sharp pics, the references to the schematic and reasons for the mods are fantastic learning experiences for the rest of us.
    Keep them coming Lee and thanks a million for inspiring us by also making it look easy. Wonderful references for the future.
    Cheers.
     
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  18. BLAH BLAH

    BLAH BLAH AK Subscriber Subscriber

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    Second that! :thumbsup:
    Have a soft spot for the old 555A...my very first Sui amp!
     
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  19. Leestereo

    Leestereo Super Member

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    Interestingly, the owner of one of the 555A that I had restored and upgraded was able to compare its phono stage to the recapped (but with capacitors that matched the stock values) phono stage of a second 555A that he owned, as well as to his Schiit Mani stand alone phono stage (http://www.schiit.com/products/mani). In this shootout, the restored/upgraded 555A phono stage was the winner: much better than the stock values recapped version and slightly better than the Schiit Mani.
     
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  20. BilboBaggins

    BilboBaggins AK Subscriber Subscriber

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    And this is why Ben is my go to guy for restorations. I love the work he does!
     
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