sansui au-717 work in northern va?

Discussion in 'Exclusively Sansui' started by itazura, Oct 11, 2017.

  1. itazura

    itazura New Member

    Messages:
    23
    I've been a very happy AU-717 owner for the past 13 years (thank you, AK forums, for that excellent recommendation). I've recently started to detect an audible hum through my speakers whenever the amp is powered on, even with the volume pot all the way down. Changing sources doesn't change anything, nor does toggling the integrated/separate switch on the back of the amp.

    Any thoughts on what might be causing this? I had the amp worked on right after I bought it (by AK'er merrylander), but it's been so long that I don't recall exactly what he did. I just know that it has sounded really nice to my ears for all these years (and continues to... except for this darned low-level hum).

    If this is something that calls for review by an expert, can anyone recommend a technician in the DC metro region?

    Thanks for your help!
     
  2. itazura

    itazura New Member

    Messages:
    23
    I wanted to briefly follow up to say that I'm pretty sure I've eliminated ground loop hum as the source of the noise (I get the hum even with all input sources disconnected from the amp).
     
  3. grillebilly

    grillebilly Empty Head Subscriber

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    Location:
    Fairfax VA
    First thing I would do is clean all the RCA jacks. Then remove the cables one at a time. I'm not saying it's going to fix it other than I've had cables mess with me a couple times in the past.
     
  4. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

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    Location:
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    Make some shorting plugs out of old RCA Jacks. Short the center and outer connections together to short it. Then put them in the AUX plugs, and set the unit up as follows. All tone and balance controls centered, loudness off, volume all the way down. Turn on unit with selector to AUX. Do the same with it in Tuner, Phono, Tape Monitor etc. REPORT ALL FINDINGS Above and BELOW.

    Disconnect the PREOUT/MAIN IN Jumpers and make sure ANY switch that says connected/separate is in the separate position. Turn on and listen for hum.

    With the switch still in separate position, run a pair of RCA's from the preouts, to ANOTHER AMP MAIN IN. Listen for Hum.
     
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  5. itazura

    itazura New Member

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    23
    Okay, here goes:

    Test 1: With all tone balance controls centered, loudness off, volume all the way down (and, for good measure, tone control circuit defeated), with shorting plugs tested in each of the following inputs, sequentially:

    1. AUX: hum still there
    2. Tuner: hum still there
    3. Etc.: hum still there

    Hum persists and is unchanged in volume or tone irrespective of selected inputs and irrespective of input connector shorting status.

    Test 2: When jumpers are removed and pre-outs are fully decoupled from main in, hum is gone. (Okay, that's progress...)

    Test 3: Unfortunately, I don't have on hand another amp with main-ins that I can use to carry out your final recommended troubleshooting step. Would it suffice to run from pre-out of Sansui to line in of another amp?
     
  6. grillebilly

    grillebilly Empty Head Subscriber

    Messages:
    14,531
    Location:
    Fairfax VA
    If you have another receiver that has separate main and pre you can use it as either an amp or as a preamp, and vice versa. Connect with RCA cables.
     
  7. itazura

    itazura New Member

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    23
    Well, I don't know if this was a sufficient approximation of the final recommended troubleshooting step, but I didn't have another full-sized amp handy, so I went from the preouts of the Sansui to the inputs of small headphone amplifier (a Fiio A3). With the the Fiio set to High gain setting, and using headphones, I detected no hum.
     
  8. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,150
    Location:
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    Which means that the hum is being generated in the pre-amplifier section or the power supply. Flip the power cord plug 180* in the wall socket and see if the hum is worse or better.
     
  9. itazura

    itazura New Member

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    Not discernibly worse or better, with power cord plug direction reversed.
     
  10. lbcgav

    lbcgav AK Subscriber Subscriber

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    Location:
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    Wouldn't it be the power amp that's causing the hum? He said no hum from pre-out to headphone amp.
     
  11. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes that's a bit puzzling....

    As he also said...
     
  12. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Location:
    Mississippi
    Might take the bottom cover off and look at the bottom of the four main caps and see if any of them show signs of leakage, don't touch anything though, they can deliver a nasty shock. Hum is often caused by large amounts of ac ripple which would appear if the main caps started to fail even with the snubber caps across their terminals--
    -Lee
     
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  13. skippy124

    skippy124 AK Subscriber Subscriber

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    Location:
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    Did you check the output of the 717 in connected mode using headphones as per your check using the pre out of the 717 connected to a headphone amp?
     
  14. Sebastien

    Sebastien AK Subscriber Subscriber

    Messages:
    73
    I have an AU717 awaiting restoration with the same problem, in my research i found this - it may help you too.



    http://audiokarma.org/forums/index....estoration-upgrade-of-a-sansui-au-717.641945/
     
  15. itazura

    itazura New Member

    Messages:
    23
    Just tried this now. Sansui pre-outs to headphone amp to headphones = no discernible noise or hum, whether the amp is in separate or coupled mode.

    So, in summary...

    Amp in coupled mode: hum through speakers, but no audible hum going from pre-outs to headphone amp to headphones
    Amp In separate mode: NO hum through speakers, no audible hum from pre-outs to headphone amp to headphones


    Maybe the headphone amp just isn't well matched with the Sansui pre-out level or impedance? I used two different sets of headphones and cranked the headphone amp all the way up.

    As Hyperion noted, above, it's puzzling.

    Thanks for everyone's help with suggestions.
     
  16. itazura

    itazura New Member

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    23
  17. skippy124

    skippy124 AK Subscriber Subscriber

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    Location:
    Sydney Australia
    Just confirming that you have tried headphones plugged into the 717 headphone out and with the separated/connected switch set to connected and you can or can't hear hum?

    Cheers

    John
     
  18. itazura

    itazura New Member

    Messages:
    23
    Ahh, I see. Thanks for clarifying.

    Simply using the amp's headphone jack:

    1. With the amp in coupled/integrated mode: hum in headphones; same hum in speakers
    2. With the amp in separate mode and jumpers removed: no hum through headphones or speakers
     
  19. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Location:
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    I would suggest that there was something wrong with the +/- 33V regulators, (i.e. not regulating any more) these are the supplies for the pre-amp and tone circuitry, but having both fail would be a bit unusual.

    And on top of that the symptoms only partially suggest the pre-amp is the problem area, anyway, I would look there first. Do you have a multimeter & know how to read a schematic and how to use the meter?

    It may be better for you to get this to a tech for an experienced look at this one.
     
  20. itazura

    itazura New Member

    Messages:
    23
    Can anyone recommend a good technician or shop in the Washington D.C. metro region? I'd be willing to ship the amp, but would much prefer taking it to somebody local.

    Thanks again for all the pointers and troubleshooting suggestions.
     

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