Sansui AU-9900A

Discussion in 'Exclusively Sansui' started by SanthoshA, Feb 13, 2018.

  1. SanthoshA

    SanthoshA Member

    Messages:
    88
    Dear All,

    A friend of mine has recently sourced the Sansui AU-9900A, it kind of runs very very hot that the heat sink is hot to touch, and he is using a cooling fan to remove the heat .

    And this is regarding the bias adjustments, i know this has been discussed already.
    Basically we do the calculation based on milli volts and then adjust bias accordingly based on the emitter resistors used, and since the 50ma value is for the entire driver board, we go for 20ma per side.

    And as per the schematics the emitter resistors are 0.33ohm, this leads to 6.6mv across the left and right channels.

    There are couple of points to check, firstly if the bias is adjustable or not(which i am unsure) , and next can these points be used as test points when adjusting bias, instead of probing the emitters directly?

    upload_2018-2-13_18-41-24.png


    As per the above picture, the voltage across the pins 09 and pins 11 should give us the bias voltage(i have outlined in red) ?
    Pin 9 is before the emitters of TR01(2SD386A), and pin 11 is before the emitters of TR01(2SB541A).
    The bias voltage should be the same across the pairs as per understanding , please correct me in case i am wrong.

    In case the bias test points which i have picked are wrong, please let me know and i will go by probing the transistors emitters instead.

    Thanks a lot for your humble guidance and support.
     

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  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Location:
    Hertfordshire, UK
    Yes - that's fine, those connections go back to the protection circuitry which monitors the voltage at those points.

    You are correct to say that measuring across one pair of emitter resistors should give ~20mA.

    (50mA per channel comprising 20 + 20mA + ~10mA for the driver transistors).
     
    Last edited: Feb 13, 2018
    SanthoshA likes this.
  3. SanthoshA

    SanthoshA Member

    Messages:
    88
    Thanks Hyperion !
     

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