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Replacing AU-X1 F-2772 Phono Mother Board

Discussion in 'Exclusively Sansui' started by Hyperion, Aug 10, 2018.

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  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Original Mk2 Phono Mother Board - with replacement relays
    IMG_2425.JPG
    Side view.
    IMG_2426.JPG

    New board fully rebuilt.
    IMG_2427.JPG
    Old board - Empty!
    IMG_2428.JPG

    There are just 2 (carbon film) resistors on this board, a 33Ω and a 5.6Ω - the 5.6Ω had drifted to 7.4Ω so it was replaced, along with the 33Ω for completeness.

    The new board is beautiful, a top quality replacement designed by AK's own Ronito6. This is particularly for anyone with a Mk1 board, which has a bewildering array of factory modifications to make it stable. But also for anyone with a Mk2 board wishing to rationalise the mounting of the much needed replacement signal relays which have a different PCB 'footprint' compared to the old unreliable relays. Ron was also significantly helped by AK member Willy6 with installation testing & tweaks and ordering boards from the US based PCB fabricator.

    The topside silk screening has been much enhanced by indicating the colours of the connecting wiring, making it a very easy job to wire back into the unit.
     
    Last edited: Aug 11, 2018
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  2. SansuiJavier

    SansuiJavier AK Subscriber Subscriber

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    It's great to get a clone of a board, and very laborious. It would be ideal to find a clone of the F-5693 card of the Sansui X-701/901. It is a board very delicate to the temperature, I have one with several tracks raised. I looked at methods to make it new but it is very very difficult. You have done a great job.
     
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  3. Ronito6

    Ronito6 Super Member

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    Thanks for the thumbs up on my 2772 Hyperion.

    In case anyone cares or is wondering...
    Willy6 asked me, wondering if I could make this board a reality. And since he and I are the same in our "What the hell. Why not give it a shot." attitude. I gave it a shot. And it worked.

    Might a parts list be offered please?
    I got 4 or 5 guys here on AK who will likely be referencing this thread rather soon as they install these new boards. I am sure they will appreciate that bit of detail from a real EE guy, rather than my amateur best guesses.

    I guess the big Q for me here is: Is there any difference / improvement sonic-ally?

    Is there an O scope test to show?

    Oh...BTW...one of the two holes I designed into this board's star ground point is intended for the Kuehne flat amp stability modification.

    I am rather sputtering now. (Not unusual for me, but ....I'll just stop here.)

    Looks good that board in your hands!

    Thanks for installing it!

    Ron
     
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  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I'll see if I can put something together - I can see this would be useful for someone upgrading a Mk1 board by replacing it with a new board.
    No difference sonically, except maybe a small reduction in random noise pickup. If there is a reduction, it will be due to being able to mount the signal relays directly on the board.
    No, nothing really of interest to see.
    I simply used the existing solder tag for this - but this may not be present on earlier X1 models maybe those with the Mk1 board?
    LOL - you're doing fine. :thumbsup:
     
    Last edited: Aug 11, 2018
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  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    AU-X1 Phono Mother Board Parts list (refers to new upgrade board or Mk2 board)

    6 x Omron G5V-2-DC24 signal relays.
    1 x 33Ω ¼ watt resistor.
    1 x 5.6Ω ¼ watt resistor.
    3 x 1N4003 rectifier diode. (replacing 10D1)
    4 x 470µF 35V electrolytic capacitors. (I used 63V here)
    2 x 0.047µF 100V film capacitors.
    1 x 0.27µF 100V film capacitor.

     
    Last edited: Aug 11, 2018
  6. Ronito6

    Ronito6 Super Member

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    Thanks!

    As I remember everything in terms of caps was some factor of 47.

    BUT it seems to work well enough.

    :banana::banana::banana:
     
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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Found it - it was 0.27µF or '274K' - corrected in post above. ;)

    The one thing I do notice is that I can just hear the relays now - suspended in mid air by the corrective wiring they just made a hard to hear faint click - but now it is more of a definite louder click amplified by the stiffness of the PCB. :)
     
    Last edited: Aug 11, 2018
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  8. Ronito6

    Ronito6 Super Member

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    Sounds good in more ways than one then. :thumbsup:
     
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  9. slimecity

    slimecity Super Member

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    Sorry to be a muppet from downunder but is there a link to this mod?

    I'm still not sure if I have the Mk1 or Mk2 board in my unit (Kevzep may know). I wont know for sure until I get in there to install this new board.
     
  10. Ronito6

    Ronito6 Super Member

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    In Germany, an EE guy by the name of Martin Kuehne discovered that the main source of the AU-X1's famous destructive oscillation originated in the grounding scheme of the AU-X1's F-2819 flat amp. http://ftbw.de/xp/amplifier-xp/sansui-au-x1-01.html

    So Mr. Kuenhe sussed out how to correct that flaw, and a couple of other flaws in the X1 in order to make is as stable and reliable as any other amp.

    Mr. Kuehne's solutions are very easy to apply. They are a must as far as I am concerned.

    Before his contribution, people tackling the issue of the AU-X1's oscillation would suggest cutting out or re-routing whole areas of the amplifier's diamond differential circuitry. Crazy. :no::crazy::no:

    Harolda discusses finding Mr Kuehne's discovery here
    http://audiokarma.org/forums/index.php?threads/the-mighty-au-x1.672322/page-8
    See posting #144

    Mr. Kuehne himself discusses his work here http://audiokarma.org/forums/index.php?threads/the-mighty-au-x1.672322/page-8
    See posting #157 to #161.

    For the first time on AK, Harolda describes and applies Mr. Kuehe's flat amp modification here
    http://audiokarma.org/forums/index....-output-transistor-replacements.684619/page-8
    See posting #151 to #155.

    For the first time on AK, Hyperion describes and applies Mr. Kuehne's DC drift fix for the EQ cards F-2770 and F-2771 here http://audiokarma.org/forums/index.php?threads/the-mighty-au-x1.672322/page-10
    See posting #182 to #194.

    ACTUALLY this last site above and it's suggested postings rather sums up the whole slew Mr. Kuehne's modifications in pictures.

    Enjoy!:thumbsup:


    Ron
     
    Last edited: Aug 13, 2018
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  11. Ronito6

    Ronito6 Super Member

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  12. slimecity

    slimecity Super Member

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    Nice - thanks Ron - so I must have posted pics of my board on a previous X1 thread.

    I will need to read up on this stuff!
     

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