Sansui AU555A Phono Issue

Discussion in 'Exclusively Sansui' started by Robby Bruce, May 12, 2018.

  1. Robby Bruce

    Robby Bruce New Member

    Messages:
    6
    Location:
    Western Australia
    So I bought a little sansui au555a a while back and ever since I bought it the phono section has had a strange issue where it sounds like interference coming from the right channel, there seems to be no bass at all from the right channel and the occasional popping sound from the speaker.

    I recently replaced all electrolytic capacitors throughout the amp with Nichicon units including the small phono board and replaced the 4 little 2sc1312 transistors with ksc1845’s however the problem still persists so I am stumped??

    It does this on both phono 1 and 2 and I have tried 2 different turntables aswell with the same results.

    The amp works exactly as it should and sounds fantastic on all other sources so I assume the problem lies somewhere within the little phono board?

    Any advice or ideas would be much appreciated...

    Cheers..
     
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  2. quadmatrix82

    quadmatrix82 Active Member

    Messages:
    261
    If you haven’t already clean the selector pot and all the switches check your soldering to make sure you haven’t created an accidental short; you could also replace the green film caps on that board it’s easy and quick to do
     
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  3. Robby Bruce

    Robby Bruce New Member

    Messages:
    6
    Location:
    Western Australia
    Yep all pots and switches have had a good dose of deoxit and appear to be operating smoothly.

    All soldering appears visually ok, also the problem was there before I started soldering in new caps etc.

    Yeah I think next thing I must try is replacing the film caps, just not sure exactly what to use for replacements.
     
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  4. quadmatrix82

    quadmatrix82 Active Member

    Messages:
    261
    Wima make good film caps and readily available online check for any other bad solder joints or broken tracks also double triple check the problem doesn’t happen on other sources
     
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  5. Robby Bruce

    Robby Bruce New Member

    Messages:
    6
    Location:
    Western Australia
    Thanks, I will look into film cap replacements and will recheck all solder joints etc.

    Definitely appears to work perfectly on all other sources, I even have my turntable currently connected through the aux input using and external preamp and it sounds fine.

    The fuzzy interference noise occurs as soon as phono 1 or 2 is selected, even without a turntable connected.
     
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  6. quadmatrix82

    quadmatrix82 Active Member

    Messages:
    261
    Have you grounded the turntable? Try a different cartridge to make sure it’s not the cartridge or try the turntable with another amp if you have one good luck
     
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  7. shicken

    shicken New Member

    Messages:
    5
    Location:
    San Francisco, CA
    The high resistance resistors can get noisy.

    390K at R605, R606
    330K at R619, R620

    Could be one of those. Swap them out with a good metal film.

    I had a bad 390K in a Sansui 2000x tone board that was causing noise.
     
    Last edited: May 21, 2018 at 1:31 AM
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