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STK-0050 replacement for SX-780 and others

Discussion in 'Pioneer Audio' started by rcs16, Jun 18, 2016.

  1. rcs16

    rcs16 Super Member

    Messages:
    2,728
    Location:
    Baldwin, Ontario, Canada
    If you want to start up a new thread, in the Fisher section, I can offer some optional improvements to this design.
    I looked a bit at this manual, there are two obvious mistakes, in the table on p13/17 they state 1.2V from the emitter R's to ground.
    and the schematics on p15/17 that the ops emitter bias is 1.2V across both 0.22 ohm emitter resistors :bs:
    It should be more like 12mV across both emitter R's for a 27mA of bias current.
     
    Last edited: Mar 25, 2017
  2. Bassblaster

    Bassblaster Super Member

    Messages:
    1,601
    Location:
    Cambridge, Ohio
    Yes i was thinking about starting up its own thread. it may be a big project...
     
  3. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    42
    Location:
    High Plains, Eastern Colorado
    I would like two PCBs please, have a SX-780 with a dead channel. Let me know when you are ready to pass them on..
    Thanks, merlyn
     
    Last edited: Mar 29, 2017
  4. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

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    They should be here in a week or so.
     
  5. marshman

    marshman AK Subscriber Subscriber

    Messages:
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    Location:
    Sewanee, TN
    Zeb, I would be interested in a pair of boards if you still have a couple available.

    Thanks,

    mm
     
  6. HBrown

    HBrown AK Subscriber Subscriber

    Messages:
    284
    Location:
    South Georgia
    I have been thinking of putting a post in the Fisher section as well for the two fisher units I put them in- but I figured if anyone searched key words it would bring them here- where all the STK replacement info is anyway.
     
  7. rcs16

    rcs16 Super Member

    Messages:
    2,728
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    I have no issue, there are already postings here referencing Fisher units and the subject title does say "others". Kinda arbitrary where this thread is positioned in AK. I think it is better to have all the info in one place vs scattered about.
    BTW, pcbway has dropped their prices down to $5/10, what a deal they offer us DIY's. Happy Easter Eggs.
     
  8. Awesomeaudio

    Awesomeaudio AK Subscriber Subscriber

    Messages:
    813
    Location:
    Sydney, Australia
    Wow Rick. 6,945 views. Praises to you and your right hand man for this. Happy Days.
    I recently acquired a very very original one owner 780 and it is mint. I mean MINT.
    I cannot pick a single flaw on this baby cosmetically. It's drool worthy.
    If, and If I need to do the upgrade, I won't hesitate to buy your kit.
    Until then, hopefully the Original STKs keep.
     
  9. Rob Thomas

    Rob Thomas AK Subscriber Subscriber

    Messages:
    126
    Location:
    Boone, NC
    Rick,

    I also have a pristine SX-780 that is running the original packs. Should the need arise, I will reach out to you. Thank you so much for sharing this. This will help protect classic receivers for the future, which is what it's all about...
     
  10. Rubber Ducky

    Rubber Ducky AK Subscriber Subscriber

    Messages:
    26
    Location:
    Denver, CO
    I've seen a post or two about using STK-0080 instead, but the responses weren't clear to me. Is the 0080 not an option as a drop-in replacement? Same unreliability issues as the 0050's being sold today?
     
  11. Awesomeaudio

    Awesomeaudio AK Subscriber Subscriber

    Messages:
    813
    Location:
    Sydney, Australia
    I believe you can use the 0080's in place of the 0050's, but ALL aftermarket STKs are pretty much a hit and miss affair unless it's pulled from a fully original donor machine.
     
  12. HBrown

    HBrown AK Subscriber Subscriber

    Messages:
    284
    Location:
    South Georgia
    80's are a different mounting pattern. The replacements will replace 80's, so 80's will probably function in a 50 circuit.
     
  13. Awesomeaudio

    Awesomeaudio AK Subscriber Subscriber

    Messages:
    813
    Location:
    Sydney, Australia
    Yes, Slightly wider. The pin outs are of the same dimension though, right ?
    One just needs to re drill and tap the mounting holes if this is to be.
     
  14. HBrown

    HBrown AK Subscriber Subscriber

    Messages:
    284
    Location:
    South Georgia
    The 80's may work. Before Rick & I worked out the replacement modules I tried to get a definitive answer on whether the 80's would work or not, and could not find anyone who had done it and had success. After installing quite a few discreet modules now and listening to them, I know I will not be messing around with actual STK's anymore.
     
  15. Awesomeaudio

    Awesomeaudio AK Subscriber Subscriber

    Messages:
    813
    Location:
    Sydney, Australia
    Is the discreet module you and Rick have going only for a 780 ?
    Will these work on the lower and higher range 80 series or will you need to engineer a model specific module ?
     
  16. HBrown

    HBrown AK Subscriber Subscriber

    Messages:
    284
    Location:
    South Georgia
    It would have to be looked at on a case by case basis to see if they were compatible with the lower units. Rail voltage, drivers, protection circuits, etc...
     
  17. zebulon1

    zebulon1 Into Phase Linear's lately Subscriber

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    I'd stuff it in and try it. Seriously.
    I'm sure you could sell them if it doesn't pan out.
     
  18. Rubber Ducky

    Rubber Ducky AK Subscriber Subscriber

    Messages:
    26
    Location:
    Denver, CO
    I've done a bunch of googling on the 80's vs 50's and I've found several threads (including some on diyaudio.com) going back to 2004 indicating that users have successfully used 80's in place of the 50's. You just have to drill new mounting holes for the larger units.

    I don't know if the 80's being sold today are any more reliable than the 50's, however. Anybody know?
     
  19. Bassblaster

    Bassblaster Super Member

    Messages:
    1,601
    Location:
    Cambridge, Ohio
    80's will work in place of the 50's. only thing is there will be less power output due to lower rail voltage (duh) and a little bit different mounting.
    USUALLY protection circuits only look for DC voltage. so it could care less about what the signal is coming from.
     
  20. HBrown

    HBrown AK Subscriber Subscriber

    Messages:
    284
    Location:
    South Georgia
    The whole intent of these replacement modules are to get away from all that speculation and roulette game of swapping modules or trying to find 'good' STK's when according to sources more knowledgeable than myself, Sanyo hasn't produced STK's since the late 80's/early 90's. The NOS of these has pretty much been used up by the vintage repair market. Anything you find is likely a substandard knock off unless you pull it yourself from a working unmolested vintage unit. You can take your chances, or embark on a new course and build something solid.

    Now there is some expense, and work involved, but in the end you get a discreet output stage for your unit made from robust modern components that has very low distortion, adjustable bias, excellent thermal capabilities, and is rebuildable.

    It's likely these modules are too much effort for someone who is trying to run a paid repair on these units- and that was not the intention. It is more for those of a diy mindset who have a nice example of a unit that they are keen to repair and continue to enjoy into the future.

    This is like an abreviated DIY amplifier project, only concentrated on the output stage of a popular unit- and adaptable to many more. You can order the pcb's and parts for yourself from the information RCS16 has generously posted. Once the PCB board and components are in hand, you have all the dimensional information needed to cut a heat spreader plate to suit particular requirements.

    It's just another option, for those who may be fed up with the uncertainty or failure of available STK's, or just want to try something different.
     
    merlynski likes this.

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