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AU-717 with a slightly different Protection issue

Discussion in 'Exclusively Sansui' started by jerrycpor, Jul 5, 2018.

  1. CDFixer

    CDFixer Number 1 USC Trojan Fan

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    Sometimes the tone board can cause protection errors. If the signal coming from the CD Player is too high you can at high volumes overdrive the tone board causing clipping of the signal once it gets bad enough the protection circuit will see the clipping as DC voltage and put the unit into protection. Some CD players can output up to a volt of signal. I have had this problem and had to reduce the output level of my CD player. The input sensitivity of the AUX and Tape inputs is 150mv. There is no maximum stated but I have found that levels of 300 to 500mv can cause overload of the tone board. As the tone board is after the volume control it is volume level sensitive.

    You will need a scope to see this but I will bet that is the problem.
     
    Hyperion likes this.

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    Guys, you are all overthinking it, the situation is very simple, he has two sets of speakers hooked up to the amplifier presenting a 4Ω nominal load, and he is running it up to full power, its simply tripping the over-current protection,
    From what I can see, the amplifier is doing a good job of protecting itself.

    I also play guitar and I am using my G22000 to play my backing tracks, not uncommon to hit 200watt peaks on the JBL L7's.
    When I was using my G9000, it would do the same thing, trip the Over-current protection.
    So, I modified it as I decided it was not a good system, and doesn't allow for any overshoot, which it should, as music is dynamic...but I digress...
     
    pete_mac and Bill Ferris like this.
  3. Bill Ferris

    Bill Ferris Super Member

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    Very well then, carry on.
     
  4. kevzep

    kevzep Its all about the Music Subscriber

    What I have noticed with Sansui, is the way they design their over-current protection it not ideal, it just has a static threshold, and when you hit it, click!! You're done.
    Its all well and good with a constant load, but when you are playing music, obviously some peaks, hit the threshold, whilst the RMS load is quite low...They needed to build in some kind of overshoot scenario....
    I was working on this with my G9000 a couple of weeks ago, I could clip the amplifier on a 3.6Ω load with a sine wave, but then go and plug it in to my JBL L7's, you barely hit 50w and it trips the protection....
    So they haven't allowed for the dynamics at all, the odd overshoot is not going to take out the output transistors....
    I am working on a solution, but in the meantime I took out the trigger diodes...
     
  5. jerrycpor

    jerrycpor AK Subscriber Subscriber

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    ConradH - it's not overheating at all, and the outputs are original.

    Bill - It sits atop a component stand with a fan blowing from one side. There is a cd player on top, but he's got it lifted off the 717 with 3 or so inch blocks that are not covering any vent slots.
     
  6. Bill Ferris

    Bill Ferris Super Member

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    Ok, I understand the setup now.
    Carry on..
     

     

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  7. jerrycpor

    jerrycpor AK Subscriber Subscriber

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    Kevzep - interesting solution to remove the trigger diodes, did you find that you could push the G9000 just a little bit farther?

    I believe that if I were to remove the base lead from TR602, it would circumvent much of the protection circuit. I read that on some paperwork that came with a couple parts that the 717 owner purchased, when he thought he might be able to fix it himself.

    I'm not planning to perform this piece of surgery though!

    The attached explanation on how the Protection circuit works on the 517 and 717 may prove helpful to somebody down the road.
     

    Attached Files:

  8. kevzep

    kevzep Its all about the Music Subscriber

    Yes you can push it more, but you really have to be quite careful, but it does raise the average output quite a lot.
    Personally I do not think the type of current protection Sansui implement is suitable if you are pushing an amplifier near it's limits....
    I'll have to have a look at the schematic and see whats going on, normally on this era Sansui its like a 3 way protection, current, DC, thermal.
    You don't want to disable the DC or thermal, they are actually quite useful...
     
  9. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    IMO those little amps are not for that kind of application.
    That amp is not a power house. John the restorer explained on one thread.
    In this application you have nominal loads of 4Ω with high volume, remember that loads are not stable and they will swing, not a surprise that you will see around 2Ω loads at some point. As Kev said, the amp is working as it should.
    You need a high current amp, just grab pro amp, use the 717 as pre and crank it up until the guy feels satisfied.
    Why mess around with protection circuit on a 45 years old little amp?
     
    Overundr1, stish and Hyperion like this.
  10. petehall347

    petehall347 the brandy coffee man Subscriber

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    tone controls might need adjusting to get that bit more . add a sub bass unit if needed .
     
  11. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I could scarcely have put that better myself. :)
     

     

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  12. petehall347

    petehall347 the brandy coffee man Subscriber

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    feed it less signal .. might need an inline adjustable attenuator . then you could make it go to ten ..
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    Because the way the current protection is set up, is not very good and does not allow the amplifiers full potential. I have done a lot of research and trialing with this.
    BUT, in this instance, it sounds like he needs more than a "bit more".
    We had already come to the conclusion that a more suitable amplifier such as a Crown or QSC should be brought into the equation.
     
  14. kevzep

    kevzep Its all about the Music Subscriber

    Most of the time, I have no idea what on earth you are talking about......
     
  15. petehall347

    petehall347 the brandy coffee man Subscriber

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    op was complaining it cut out with vol at 1pm . so if input was reduced with an attenuator like we do with dj.s to save p.a equipment damage he can get it to volume ten .. no idea if it even goes to ten . was me not being serious . sorry its hard to type what i am thinking ..
     
  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    mmmm
    nice.gif
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    10 million dollar question . why did they design it in such a way ? answers on a postcard please .
     
  18. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    To make it harder to puff blue smoke out of it.
     
  19. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    Nice, so the amp doesn't clip the transient peaks it just shuts off. Thank god he's not playing Classical, he'd be rebooting every minute...

    This thread is making me want to sell my 717 and my BA-F1
     
  20. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    I guess we now IMG_2234_zpswa0igqpa.jpg know why Sansui made the SP-5000 and SP-5500

    90 & 100 watts and 102db
     

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