AU-717 with a slightly different Protection issue

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

  1. jerrycpor

    jerrycpor AK Subscriber Subscriber

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    A buddy has an AU-717 that he's had for awhile. He drives 4 Klipsch speakers (RF82 and something similar) using the aux input. He plays CDs at very high volume levels while he jams along on his guitars in his lil studio; guitar is fed into separate amps.

    It started going into protection when he'd reach a certain volume level, so he'd been just "babying" it and not turning it up QUITE high enough to push it into protection.

    Thinking that a full restoration would solve the issue (since he said that it hasn't always gone into protection), that's exactly what I did. Pretty much every thing was performed according to Ben's recipe in the "Leestereo's Restoration/Upgrade Of A Sansui AU-717", including upping capacitance and voltage where recommended. I say pretty much, because I also replaced the filters caps (with Gold Tunes), and TR603 on the PS/Protection board.

    Post restoration, was able to dial in Bias and offset perfectly...AND the unit sounds amazing!

    BUT...the thing still goes into protection when driven hard. Seriously, he's listening at levels most of us wouldn't, but he played in a band when he was younger and want's to pretty much play just as loud during his jam sessions! The volume dial is turned up to just past 1 o-clock and is ok, take it to 2 and she shuts down.

    He says it is actually louder at the place where he used to turn it up to, and is very happy with the results overall.

    I am wondering though, why is it still going into protection after a full rebuild?

    One picture - since I didn't want my post to be "worthless" :)
     

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  2. petehall347

    petehall347 the brandy coffee man Subscriber

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    tell him to try one pair of speakers.
    also try balance all one way or all the other way
     
  3. pete_mac

    pete_mac Super Member

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    The 717's protection circuit includes overcurrent protection. Driving a two pairs of 8 ohm speakers (presenting a 4 ohm load if connected in the typical manner to the Speaker A and B outputs of the amp, and both driven simultaneously) to extremely loud levels, requires a fair whack of current - and to be fair, this is not the strong point of most Sansuis.

    It sounds like he either needs more efficient speakers (although the RF-82 are 98db sensitivity which is pretty high for a slimline floorstanding speaker!) or a more powerful/grunty amplifier.

    Or, of course, turn the volume down ;)
     
  4. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    Because he's pushing the amp past it's capabilities.

    The thing must sound like crap clipping most of the time before it just can't take it anymore.

    Tell the guy if he wants to do what he's doing he needs to go buy a power amp. Maybe one about 250- 500 wpc, maybe a proamp as it's will be better sound quality than he has pushing the 717.

    He can then use the 717 as a preamp without smoking it or his speakers, In fact I'm surprised his speakers aren't blowing up.

    BTW, he might just think the system was louder before, he might just be loosing hearing as he ages.
     
    Last edited: Jul 6, 2018
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  5. pete_mac

    pete_mac Super Member

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    I forgot to say... nice work on the rebuild too! She looks an absolute treat!
     
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  6. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    Because something like this is more suited for his needs.
    [​IMG]
    +1 about the recap...very neat work.
     
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  7. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    Agreed

    I have a 717 that will not go out of protection and would love someone to rebuild it.
     
  8. Tom B

    Tom B AK Subscriber Subscriber

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    I also believe the issue is the 2 sets of speakers, bringing the impedience down at 4 ohms or less.
     
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  9. kevzep

    kevzep Its all about the Music Subscriber

    1, you can't push it beyond its capabilities because the over-current protection will trip the protection.
    2, therefore, its can't sound like crap because you can't push it into that zone
    3, unless the speakers are horrendously underpowered, you'll never blow any speakers up because you actually can't clip the amp with that kind of dynamic load on it.
    4, agreed, he needs a more powerful amp, about 250 watts as you say, that is a good size for what he wants to do, and one that can drive low impedance loads, like a Crown or a QSC powerlight or something, plenty of options out there...

    I use backing tracks when I play my guitar, I use my Sansui G22000 for that, its a good sized amplifier for such purposes.
    One set of JBL L7's, it all kicks arse....very nice!!
     
  10. jerrycpor

    jerrycpor AK Subscriber Subscriber

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    Thanks Pete - It gets plenty loud with just a pair of speakers, but he wants all four :)

    Thanks Pete - I think a more powerful amp is the ultimate solution, cuz he don't wanna turn it down, wants to turn it UP lol
    Thanks 4-2-7 - actually, we don't hear it clipping, and the distortion is barely audible at blistering volumes...I think you're right though, that a more powerful amp is in order, and, he likely suffers hearing loss heh heh

    Thanks for the restoration compliment - first Sansui rebuild and it wasn't that bad.


    Tom - yep, that seems to be the consensus.




    Yup, that would be one way to go! Thanks for the compliment!

    Thanks kevzep - You nailed it, it never sounded like crap, just really loud then nothing.

    Well, thanks guys for all of your replies, will advise buddy to step up his WPC game, and get a beefier amplifier.

    ! I hope I have utilized the quote feature properly...if not sorry :)
     
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  11. petehall347

    petehall347 the brandy coffee man Subscriber

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    i was trying to see if it was behaving properly . hence try one pair of speakers .. theory says he should be able to crank it more before it cuts out . he could then maybe use a line out to another amp to feed the other speakers .
     

     

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  12. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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    I used to push Sansui into the sound like crap zone all the time LOL.

    Stacking speakers in all 4 corners of the room and play it as loud as you can helps a lot:p

    IMG_0185.JPG IMG_0186.JPG IMG_0187.JPG
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    Well in actual fact you can't, because the current protection will not allow it, remember, I work on this stuff all the time.

    The only way you can is of something is wrong with it and the over-current is not working correctly.
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

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    how does over-current work on this one ? i had a quick look last night but was full of whisky and beer .. i never saw that transistor on the amp schematic thats often there . is it like the pioneer one on protect circuit ? or some other way that i have seen ?
     
  15. ConradH

    ConradH Addicted Member

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    Is it overheating? OK, too simple. Did you keep the original outputs? I've run into the problem with old Crowns where the outputs break down a bit lower than they need to. Everything is fine until you drive it hard. The only way to tell is to put them on a curve tracer. Could be other transistors too, but less likely.
     
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  16. kevzep

    kevzep Its all about the Music Subscriber

    It will probably be like the other protection circuits in Sansui of the time. Voltage Drop over one of the emitter resistors, then another resistor which then, in turn will fire a diode which will trigger an SCR which will then through another circuit turn the protection relay on or turn the speaker relay off and fire the vibrator to flash the protection indicator or power indicator...

    Do yourself a favour Pete, lay off the booze man!!
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

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    for once i am sensible with the booze . or try to be . at least its top shelf stuff . will look at schematics to take it in . p.s a double single malt starts the day off well if doing smd work .. can actually stay calm enough
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

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    ok yes i see it now pin 28 etc .. .. will the amp survive if d02 is modified ?:D
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

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    went through this with a neighbour years ago . he is now happy with his all in one that doesn't blow up even when shorting the speakers . i ended up with the upgraded amps
    ps
     
  20. Bill Ferris

    Bill Ferris Super Member

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    Yes, ConradH, I wonder, is the Sansui getting proper ventilation(plenty breathing space all around it, especially important being that it`s driven hard).
    Comfortable room temperatures are important, as well.

    Is any equipment stacked on top, blocking ventilation holes/slots, or is it inserted in some kind of enclosed cabinet ?
    Something to consider, especially if the top of the cover is very hot when it goes into protect..

    Just a thought folks, as I`ve seen this situation many times before when audio equipment is sited to look good(WAF neat) without thinking about thermal considerations.

    IMHO/E. Heat, power line surges, & spikes are not good for any, especially, SS electronic gear.
     
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