Sanui AU-Alpha907 Limited - IN DA HOUSE!!!

Discussion in 'Exclusively Sansui' started by skippy124, Jun 22, 2015.

  1. Shavalievdd1

    Shavalievdd1 New Member

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    10
    John thank you for your reply, one of the PSU caps 8200mF 63V is bulged a little bit, i checked the bottom of PSU caps and there are no signs of leak so can i consider them in good condition? please see photo of the bottom plate and top of the caps (bulged cap is on the left side).
    regarding smaller capacitors, i checked the condition of glue on all plates and there are no any dark spots.
    in fact i have hardly noticeable (need to get quite close to speakers to hear it) background noise like old TV set static noise in both channels and this upsets me. unfortunately i'm not a specialist and can do only basics checks and soldering and there are no good services around me, so may be you can give me some suggestions regarding this, of course i understand that it's pretty hard to find a problem without device in your hands.

    also English is not my native language, but i do my best)

    thank you
    denis
    29020664402_71b77f2a8a_o.jpg 28839398380_4cb2d0b67b_o.jpg
     
  2. pete_mac

    pete_mac Super Member

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    2,708
    Location:
    Sydney, Australia
    Those caps are fine. They vent via the rubberised bottom seal, not the top of the cap. The plastic some can contract and distort over time.
     
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  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    +1
    I am in complete agreement with Pete on this.

    PS your English is very good. :thumbsup:
     
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  4. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    gentlemen thank you for your valuable input, you've helped me quite a lot)
     
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  5. JOMARK911

    JOMARK911 Super Member

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    As both the above gentlemen said , there is nothing wrong with your PS caps. If you have this funny like static noise you hear up close the speakers it's all the smaller ones electrolytic and non that need to be changed. It's an awful big job on your amp. Refer to someone qualified enough to do this for you . This is not a usual amp to start messing around with it's caps .
     
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  6. JOMARK911

    JOMARK911 Super Member

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    PS , I've always liked this kind of caps configuration on the power amp , SANSUI used to implement. Four big cans on the main ps bank , and the other smaller two on the power amp directly. On B2301L either European or jap version the smaller ones are four ,two on each channel, directly on the output transistors.
    Anyway I like this kind of design , and to be honest never seen it elsewhere . Some design small things that make such nice amps. Although not all SANSUI amps had this kind of design , all the totl units from 1983 and on had it , with B2301 as the starter.It coincided with the implementation of a-x balanced topology.

    PS , bold , not on the output transistors , but on the voltage amplifier, ie driving boards.
     
    Last edited: Aug 23, 2016
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  7. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    Thank you for your suggestions i wont touch small caps as i'm not a professional to complete such repairs properly.

    By the way, i have small scratches on the front panel of my sansui, so i want to polish, but unfortunately i cannot dismantle the volume regulator. Can anybody suggest me the way how to remove it. i see a small hole on the side- is it for a screwdriver or hex drive?

    also any tips regarding polishing of the sansui paints?

    thank you
    denis
     
  8. AUD101

    AUD101 Parsley The Lion!

    Messages:
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    Location:
    "The Big Smoke" - UK
    Going by previous Sansui's - the volume control knob is usually secured to the pot shaft by a 1.5mm hex grub screw
     
  9. pete_mac

    pete_mac Super Member

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    Location:
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    Denis, unfortunately you can't polish the brushed metal front fascia of this amplifier. You will only further damage the appearance. :( You are better-off leaving it as-is.
     
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  10. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    thank you pete_mac, can you help me with one more question. Yesterday i checked the bias current on each channel and reading were about 30mV and quite stable, also i checked the temperature on heat sink by temperature gun and it showed 57C. Is it fine for 907 MOS limited?
    Sansui alpha 907 limited (not MOS version) adjustment manual says 28.6mV, so i guess i can consider my mV measurements within the operation limits but temperature looks quite high for me.

    thank you
    denis Sansui Alpha 907 Limited Settings #1.jpg
     
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  11. czubsi

    czubsi Active Member

    Messages:
    112
    907 limited temp. normal : ca 40 st. ... 57 This is a lot but not very much :)

    1) check the setting jvr5 !!! (selector position : integrated , volume max , voltmeter to the speaker outputs !!!)
    2) check the power transistors (MOS)
     
  12. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    czubsi thank you for reply, but my sansui is 907 MOS limited, and as i know there is no jvr5 potenciometer in it. Bias current is 30mV, should i try to reduce it?
     
  13. czubsi

    czubsi Active Member

    Messages:
    112
    AU alpha 907 limited and AU alpha 907i MOS limited to two different designs !!!
    Both set up differently !!!

    907 limited to construction based on 907 XR
    907i MOS limited to construction based on the 907i ...

    In 907i MOS limited you must first set the driver and it is not easy ....
    you have to follow the procedure of the model 907, 907i and 907 Lextra ...
    you need to remove the front panel ...

    My advice :

    set the value of the model B2102MOS or 27 mV (This is also the scheme)

    Take a test driver or measure the value of the voltmeter to the speaker outputs with minimum volume and then at max volume and write to the forum what came out.
    Of course selector set to integrated !!!
     
  14. pete_mac

    pete_mac Super Member

    Messages:
    2,708
    Location:
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    Hi czubsi!

    Nice to see you posting here again.

    Please stay around - your contributions on the Alpha series amps are valued. :)
     
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  15. czubsi

    czubsi Active Member

    Messages:
    112
    driver setting in 907 L extra

    Check whether you are in the same
     

    Attached Files:

  16. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    thank you for test procedure, i checked my 5668 board and readings between hot/cold and hot/gnd for each channel are quite stable and around 0mV
    29228602736_3d61ee88bd_o.jpg
     
  17. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    speakers output readings
    left channel volume min -5.7mV volume max -36.8mV
    right channel volume min 6.4mV volume max -25mV
     
  18. czubsi

    czubsi Active Member

    Messages:
    112
    the tragedy is not :)
    set still 27 mV for the power transistors.

    ... And listen ....
     
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  19. Shavalievdd1

    Shavalievdd1 New Member

    Messages:
    10
    Czubsi, I adjusted the bias current from 30mV to 27mV and sound changed dramatically, it became more clear and sweet. Thank you for suggestion. Temperature is still high and about 55C, also I checked power supply diod bridge temperature and that close to 50C.
     
  20. JOMARK911

    JOMARK911 Super Member

    Messages:
    2,463
    Location:
    Athens Greece
    The sound became more clear and sweet by reducing Bias by 3mv? No way my friend.
     
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