STK-0050 replacement for SX-780 and others

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

  1. HBrown

    HBrown Active Member

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    I don't think the plate thickness is relevant except to have enough engaged thread length to get the devices fastened down adequately.

    What I think is important for best heat transfer is the flatness of both the plate AND the original heatsink. I file & then lap my heatsink plates with compound on a piece of glass. My 780's heatsink was not perfectly flat when I put a straight edge across it. The 780 heatsink is a flat piece bent into a 'U' shape. The mounting surface proximity to the bends and the pressure of the brake dies from the bending operation leaves it not perfectly flat. Mine had a tiny bit of a 'wow' to it. I can't recall if it was convex or concave- so I removed the heatsink and knocked the mounting surface down flat with a fine bastard file. Didn't take much. My buddy whom I made modules for did not do that with his and he has had no problems so it may not be enough to cause an issue. My suspicion is the original STK's will flex a minute amount and conform to the surface somewhat. Our 1/4" or 3/16" solid heatsink plates will NOT flex under the light tension of those two mounting screws. I originally noticed it when my very thin layer of heatsink compound did not squish out evenly around the edges of the plate when I first bolted the plates down. After my attention to the heatsink, it did squish out evenly.

    Going too far? maybe. I tend to get a little OC about small details like that- but I rarely have to re-lick the same calf.
     
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  2. HBrown

    HBrown Active Member

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    Rick, he's talking about an extra stiffener plate that is attached to the other side of the 780 heatsink that has another set of mounting screws that protrude through from the backside. They miss the smaller original STK module, but will hit the heatsink plate. I should have mentioned that detail but I dealt with it early on like Zeb did and forgot about it. That may have been pioneer trying to combat the little bit of 'wow' in the heatsink I mention in my post above. Either that, or an attempt to get more thermal mass right at the point of heat entry to the sink. I can think of no other reason for the stiffener plate. It's not a module fastening plate, because I think I recall the module mounting screws go clean through holes drilled in the stiffener. I think my buddy left the extra plates off of his when he put the modules in. I'm almost certain I have read before where not all SX-780s had the extra backing plates bolted on the backside of the heat sink.
     
    Last edited: May 18, 2017
  3. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

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    Rick, something occurred to me, and I want to "get it down" for consideration.

    Not trying to denigrate a tremendous accomplishment. This is already legendary AFAIAC.

    The original stk-0050 would be killed by about a 1 second short to ground.

    Is this also probable in the replacement? Has this been answered in the thread and I just missed it?

    Does the tremendous current carrying capability of the power transistors used save the day?

    I remember in my experimenting that those overloads would smoke resistors in the module I was fooling with
    after I smoked their transistors, then used used more robust replacement transistors.
     
  4. rcs16

    rcs16 Super Member

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    Hi Mark,
    I did not incorporate any over current protection in the replacement STK module design.
    Shorting the o/p on these stk replacements will result in the same issue as the originals, maybe they will last a few ms longer.
    I have suggested to invest in supply line fuses as a way to save the o/p stage with a direct short.
    I recall many moons ago that you mentioned that it was a nice to have the OCP circuit included. I agree, it is a nice to have. I have another design version that has the OC protection parts like they used in the SX-880/980 design. Need some re-wiring on the protection ckts as done in the SX-880/980 design. It can be done on its own as an addition. Even with the relay solution, I have heard of situations where the contacts arc together.
     
  5. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Got a question with regards to mounting on the units heatsink. Could you mount the assembly to the vertical part of the heatsink and still have adequate sinking to keep this cool? Or am I blowing smoke out my a** again. With the minimal clearance on the bottom I would think mounting it to the vertical sides would be a bonus in that respect.
     
  6. rcs16

    rcs16 Super Member

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    I think the module could be mounted on the vertical part of the heatsink, but is it necessary?, based on the pic HB took, there is enough clearance for the module.
    Those w/w posts for the supplies look to be about the same height.
     

    Attached Files:

  7. Caughtthebug

    Caughtthebug AK Subscriber Subscriber

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    I have use 3/16 plate and had no clearance issues. Larryderouin i think I have enough aluminum plate left to make you a set. and I made a template for all the holes.
     
  8. Artie

    Artie AK Subscriber Subscriber

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    This is an amazing thread. I can't wait to order some boards and dust off the ole SX-780.

    Special thanks to rcs16 and HBrown for their efforts in this project. And thanks to everyone else who contributed.
     
  9. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    I have a ton of them.
    PM me. Selling at cost.
     
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  10. Artie

    Artie AK Subscriber Subscriber

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    Hey zeb. How do I PM you? Is it the "start a conversation" link?

    Nevermind. I found it. :)
     
    Last edited: Jun 2, 2017
  11. Artie

    Artie AK Subscriber Subscriber

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    Hmmm . . . this is interesting. Look at the schematic for the unobtanium Yamaha CR-1040 output module. (Fig 1)
    Then look at the amp schematic. (Fig. 2). Pins 5 & 6 simply have a cap across them. Same for pins 4 & 7, with an additional cap going from 7 to 9, and from 4 to 2.
    If we redraw the module schematic, (fig.3), we end up with what is essentially this board. Same pin-outs and sequence. I wonder if this board, with some minor mods, could work as the replacement for the CR-1040?

    Examining this even closer, the cap from pin 4 to 7 is, essentially, C2. And the cap from 4 to 2 and from 7 to 9, are almost the same as C1 and C3. This module might just be plug-'n-play.
     

    Attached Files:

    Last edited: Jun 2, 2017
  12. Artie

    Artie AK Subscriber Subscriber

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    My boards arrived today. These look killer. Can't wait to get started on this project. :banana:

    Thanks zeb. (Oops. Meant zeb. Corrected.)
     
    Last edited: Jun 5, 2017
  13. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    That was fast.
    My brother is finalizing the heatsinks. It shouldn't be to long.
     
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  14. james cox

    james cox jovial99 Subscriber

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    Last edited: Jul 12, 2017
  15. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Seems like the one piece besides the board that's not readily available in ready to use form is that aluminum plate. Anyone here know the machining business? What would it cost to have a bunch of them made, similar to the boards?
     
  16. rcs16

    rcs16 Super Member

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    It is actually a fairly easy thing to do to make the Al plates up yourself. You can buy the 1/4" AL plate from HomeDepot and use a hack saw to cut to size, bastard file to file off burrs, shape, fine grit emery cloth to polish, hand drill/bits and not absolutely need a drill press, just have to drill at close to 90 degrees. Must use the right size bit (posted earlier) and get a 4-40 machine screw tap and hand tapping tool. Basic High School machine shop stuff.
    PM Zeb, he was getting someone to make some up, not sure if they even got completed
     
  17. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Ha, I did, then realized he was also the one with the boards I asked about earlier, so my two PMs make me look like a doofus, but anyway.

    I was thinking this thread is long enough that it would be great if we had consolidated pictorial instructions with all the awesome hints that have been posted. Takes time for someone to do though.
     
  18. 8xlaxx

    8xlaxx Super Member


    @zebulon1

    Thanks for the boards! They arrived yesterday with no damage to the envelope. :thumbsup:

    Keep me posted on the developments of the heatsink/aluminum plate,... you have a buyer once they are completed.

    8xlaxx
     
  19. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    Working with a new source. Should have something soon (This week).
     
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  20. 8xlaxx

    8xlaxx Super Member


    Sounds great!

    Quick question,...
    A few posts/pages back it was mentioned that some of the parts from Mouser were backordered or 'unobtainium' with advice to look at Digi-Key, Arrow, other vendors, etc. Is the Mouser BOM up to date now and parts ARE available? Wasn't sure on this.

    Apologies if I read that wrong. Thank you.
     

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