Sansui 5000A Low volume sound distortion

Discussion in 'Exclusively Sansui' started by grindfix, Aug 11, 2017.

  1. grindfix

    grindfix AK Subscriber Subscriber

    Messages:
    185
    Location:
    New Albany, OH
    I have been working on this one for quite some time.
    Originally receiver had no sound from both channels. I didn't even try to investigate since F-1040-1 looked untouched and black squares had corroded green spots on their supports and on transistor bodies.

    My first round was replacement of outputs, all electrolytic capacitors on F-1040-1 boards along with TR 803 and TR804. Replaced black square "Origin" temp compensators with NTE-605a pairs. Cleaned all controls and Adjusted Bias and output voltage. I was exited to have sound through headphones, but as soon as speakers were connected, sound was distorted through both, speakers and headphones.

    Scope clearly shown DC in output. Replaced all 4 cans with 3300 @ 100v Nichicons, replaced all 8 in diode stack and rebuilt protector board (diodes, zeners, e-caps). Re-adjusted amplifier boards and fired it up.
    Great sound at normal to higher volumes. Low volume is another story. Sound is distorted and jittery almost like bad cell phone communication. It breaks through with audio signal peaks and gradually goes away as volume is increased. No DC in scope pattern. Input signal from preamp is good too. Anyone ever seen this?
     
  2. tom3

    tom3 Super Member

    Messages:
    1,629
    Location:
    So. Ohio
    Don't know if this would show anything or not, but you might try turning down the rear panel level control, bringing up the main volume, see if that clears up the sound at the same listening volume?
     
  3. Robisme

    Robisme Sansui Enthusiast Subscriber

    Messages:
    11,354
    Location:
    Martinez California
    Sounds like low bias current.

    Rob
     
  4. grindfix

    grindfix AK Subscriber Subscriber

    Messages:
    185
    Location:
    New Albany, OH
    I was working on 3 different Sansui 5000 series at almost same time and mixed-up some information. All 3 units have 3 different driver boards.
    F1040, F6013 and this one with F1040-1. This one was modified using skippy124 mod.

    http://www.audiokarma.org/forums/index.php?threads/sansui-frequently-asked-and-more.144580/page-22

    I played with rear volume limiter pot with no success to report. Bias is set to factory spec of 23ma between each fuse terminal with fuse removed.
    Would it be possible that new and more powerful MJ15024G transistors need higher bias regulation?
     
  5. blhagstrom

    blhagstrom Mad Scientist, fixer. Subscriber

    Messages:
    12,066
    Location:
    Duvall, Washington
    FWIW my first 5000 was an A version and the volume pot was crapola.

    Maybe check the signal there.
     

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