Sansui AU-777A xmas break rebuild

Discussion in 'Exclusively Sansui' started by smurfer77, Dec 23, 2014.

  1. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
    Location:
    San Francisco
    Sometimes the clipping at one side (crest or trough) is 'hiding' if your settings are way off centre.

    You should be able to centre up so you have clipping at both top and bottom using just VR801 and VR802. Starting from a low volume, turn up the volume until you just have clipping on your one channel..... just a tiny bit of clipping on your bottom part of your sine wave. Then adjust the appropriate VR (801 for L, 802 for R) - turn in the direction such that your tiny bit of clipping disappears. (If the amount of clipping is unaffected by VR adjustment something is wrong, possibly with the VR, but it's unlikely both VRs are dead). Then turn up the volume a bit more and you will get clipping again... adjust VR again so that you remove the clipping and repeat and repeat. At some point both channels will clip. Make it so as you turn up volume you just go a bit into clipping on both channels at the same time. Repeat process for other channel (using other VR). Others have slightly different approaches. I like this way if you are really far off centre, to help find centre and it's quite precise to make onset of clipping occur at same volume for top and bottom of peak compared to visual approach of making clipping about the same level (as described in next paragraph and manual)

    Another approach is much simpler and basically what the manual says to do - just push into clipping and adjust VR so that amount of clipping is even - you should be able to affect the clipping with the VRs. If you only see clipping on one side, turn the volume up further until you have clipping on both sides, and then adjust VR so that level of clipping is similar at top and bottom (then turn down volume so you are just at onset of clipping and match it up onset of clipping). If you turn volume up to max and still only see clipping on one side you are way off centre and you might need to turn up your input voltage so you get into clipping earlier on your volume control - proceed with caution in that direction - the amp might not like being driven too hard into clipping for extended periods.

    There is a rough approach that you can use that people who don't have oscilloscopes can use, but since it sounds like you have a scope, might as well work out the proper way. if none of this works maybe start-up a thread on your issue and we can all help you

    Cheers
    David
     
    Last edited: Aug 8, 2016

     

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  2. zeste

    zeste New Member

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    Location:
    France
    Thank you for your answer,

    yes I have a scope, I just tried your first method and on the right channel I have achive to do the setting. But on the left channel, when I turn the VR, nothing happened. I think the VR is dead even if it's new. I replace it with a multi turn vishay spectrol that I tested before soldering. I will replace it tomorrow and will try again.
     
  3. smurfer77

    smurfer77 AK Subscriber Subscriber

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    1,510
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    If the VR does adjustIf you tested the VR before installation, maybe reflow the solder at the joints and check the PCB trace for damage nearby (visually, as well as checking continuity with multimeter between leg (not solder joint) of VR and nearby connected components, before replacing again with another new VR. good luck
     
    Last edited: Aug 8, 2016
  4. slimecity

    slimecity Super Member

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    3,148
    Location:
    New Zealand
    I love this perpex lid - I would love to do that with my 999 (but I would need to remove the internal metal plate shielding for maximum effect - that may not be a great idea). Was it expensive to get this lid made?

    I love how the very simple way that the outputs are mounted - I havent seen this on any Sansui I have worked on.
     
  5. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
    Location:
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    Thanks. I love it too. You can make one yourself with the right glue and tools, but to have it professionally made cost me less than I expected. I don't remember exactly but it do remember it being just under $100 including shipping across the USA. Done by the guys at "Gordon's Plastics", Fenton, MO (no connection or affiliation, aside from being a costumer for this 777A lid). FYI. I was really impressed when it arrived - they packaged it like fine art. I keep meaning to ask them to do some more things for me like a turntable cover etc. Your local CNC/perspex guys may be able to do similar. Make sure they polish the joints... makes it look much nicer.
     
    Last edited: Aug 9, 2016
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  6. zeste

    zeste New Member

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    28
    Location:
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    I change the VR and I put a 16ohm resistor and it was easier to set the clipping. The screew of the VR is blocked at the maximum value.
    Thanks again !!
     

     

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  7. zeste

    zeste New Member

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    Location:
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    Hello,

    I have a Japanese version and I would like to change the transformer by a custom toroidal transformer with 240v input but on the scheme I didn't see how much Ampere does have the 53V circuit (see pics)

    [​IMG]

    Do you have the information ?

    In the owner manual, it is specified : "Power Consumption = 165VA Max", when I calculate the power of the transformer to get this value, I get 3A for the 53V circuit. Do you think I'm right ?
     
  8. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
    Location:
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    Hi, the manual I have shows 4A on the 53V secondary. If you find a suitable transformer, that will also physically fit, do let us know. Good luck on your aussie (?) conversion.
     
  9. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

    Messages:
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    Thanks Smurfer! I was more interested in your small cap choices and where you used Wimas etc....
    Edit: that's quite the list!! Very well done!!!
     
  10. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
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    I didn't discuss much in the thread but if I recall correctly I might have used some metalized polyester film caps. Polyester gets a bad wrap from audiophiles, compared to the preferred polypropylene, but believe me the WIMA versions sound great. Basically, use polypro where you can, but often polyester is the only thing that will fit, physically, and it's still going to beat electrolytics. For the even smaller value stuff, look for C0G cermanics. Notice that some positions you can change capacitance, others you can not (but I usually increased voltage a bit) - but you are probably aware of which scenarios fall into which category. if not, ask over in your thread.
     
    Last edited: Apr 11, 2017
  11. quadklipsh

    quadklipsh Super Member

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    awesome photography and inspirational work . i wonder the effect of those film caps you installed instead of the old stock ones.
     

     

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  12. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I've compared a 555A, one with film caps and one with new electrolytics. The film caps do seem to make a difference in signal path positions especially, but a very subtle one that you may not notice. In non-signal cap position you (usually) wouldn't expect any difference to the sound. I think it makes sense to use the film caps were possible though for a few reasons, in particular in signal path where polar electrolytics were used (I know, for small amplitudes it shouldn't make much difference it it's polar or not), but also just because the film caps should not dry out and age in the same was as electrolytics.
     
    Last edited: Apr 12, 2017
  13. quadklipsh

    quadklipsh Super Member

    Messages:
    1,329
    Location:
    Lahore, Pakistan
    Then it's not worth the hassle. As I donot intend to keep an amp for ages:confused:
     
  14. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
    Location:
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    That, IMO would be a mistake :)
     
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  15. quadklipsh

    quadklipsh Super Member

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    1,329
    Location:
    Lahore, Pakistan
    ok ill keep it:biggrin:
     
  16. Pol

    Pol New Member

    Messages:
    21
    Magnificient!!!
    Hi David, is it possible to order one? please contact me, I'm very interested in this gem of plexiglass. All the best!! POL
     
    Last edited: Jul 25, 2017

     

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  17. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Plus 1 here.... Looks very cool!
     
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  18. smurfer77

    smurfer77 AK Subscriber Subscriber

    Messages:
    1,510
    Location:
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    No plans to start selling those, and it would be more expensive than most would like to pay. It's a labor of love.

    However, I have a couple more 777 variants that need to be rebuilt over the next 6 months or so, so I will definitely be having at least a couple more made up at some stage; I might make a group buy thread, or at least share the plans (I am happy to share the plans I drew up already, but they really need a couple of modifications IMO).
     
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  19. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    Sounds good Smurfer! Having multiple cases made should reduce the cost somewhat...
     
  20. Bhuvaneshwar

    Bhuvaneshwar New Member

    Messages:
    6
    PM for @smurfer77

    Awesome thread. Very detailed and informative.

    I also have a 777a and searching for tech to get it restored. Looking for detailed list of parts (type/spec/manufacturers) changed including all transistor equivalents.
     

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