Page 2 of 2 FirstFirst 12
Results 36 to 59 of 59
Like Tree40Likes

Thread: STK404-140S Question

  1. #36
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    Hey, killer job, congratulations

    Thatīs a beefy aluminum bracket your friend made; is is a piece of L shaped extrusion or a bent piece of thick aluminum plate?

    Your idea of mounting is flawless, you both strongly mounted new module *and* old supply (which is quite more complex than I thought) in available space and put power amp heatsink in the best possible place.

    Donīt consider this "wasted time" at all, but getting your feet wet on what will soon become the only (realistic) way to keep modern "orphan" amps working.

    As always, the "electronic" side of the work is reasonable; the mechanical/fabrication/metallurgical side is the deal killer for 95% "normal" Techs, simply because itīs completely unrelated and requires a set of machinery (specially shears and bending brakes).

    In the early days I was helped by local people making tin stuff: buckets, AC/ventilation/chimney ducts, farm animal feeding trays, etc. , but most have dissappeared (and the few remaining are too large to cater to neighbours) because today such stuff is bought ready made at Home Depot, Wal Mart and such, made hundreds or thousand miles away.
    Oh well.
    Juan Manuel Fahey

  2. #37
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,390
    The aluminum bracket was milled on a CNC machine out of a solid block of aluminum. It would probably be easier for someone to bend something up, but I'm lucky enough to have a friend with skills and access to expensive tools.
    J M Fahey likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  3. #38
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    These guys took the bull by the horns and made their own STK module:

    https://www.ebay.com/itm/STK-0050-Mo...8AAOSwaZJZhmtX



    Since postings donīt lst much, hereīs the direct link to sellers:
    https://www.ebay.com/usr/bobandelain...p2047675.l2559
    nickb and The Dude like this.
    Juan Manuel Fahey

  4. #39
    Senior Member
    Join Date
    Aug 2017
    Location
    Portland, OR
    Posts
    240
    Quote Originally Posted by J M Fahey View Post
    These guys took the bull by the horns and made their own STK module:

    https://www.ebay.com/itm/STK-0050-Mo...8AAOSwaZJZhmtX



    Since postings donīt lst much, hereīs the direct link to sellers:
    https://www.ebay.com/usr/bobandelain...p2047675.l2559
    That layout is so much cleaner than in any of the STK modules (real or fake) earlier in the thread. It's a smart move, surprised they aren't selling populated kits. Those PCBs probably cost $0.50 even in low volume.

  5. #40
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,390
    Yes. And, it's repairable at component level. Once you've retrofitted it, you're good to go.
    nickb likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  6. #41
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,721
    Quote Originally Posted by J M Fahey View Post
    These guys took the bull by the horns and made their own STK module:

    https://www.ebay.com/itm/STK-0050-Mo...8AAOSwaZJZhmtX



    Since postings donīt lst much, hereīs the direct link to sellers:
    https://www.ebay.com/usr/bobandelain...p2047675.l2559
    Sadly, I really don't think that will work as a drop in replacement as it's missing the voltage amplifier stages. They just have the current amplifier section. Take a look at the block diagram of the actual STK404-50:

    stk404-50bd.jpg
    Experience is something you get, just after you really needed it.

  7. #42
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    Nobody said itīs a replacement for STK>>404<<50 but straight STK-0050 , a different model, and which gives you just the "power pack" and leaves the rest of the amplifier in the designer's hands.
    STK0050 pdf, STK0050 Descripcion, STK0050 datasheets, STK0050 Vista ::: ALLDATASHEET :::

    Specifically designed to repair "STK-0050 Replacement for SX-780 and others"

    These guys offer the design for free, including Gerbers and such :
    STK-0050 replacement for SX-780 and others | Audiokarma Home Audio Stereo Discussion Forums

    A full amp based on a smaller brother but basically same idea:
    Juan Manuel Fahey

  8. #43
    Junior Member
    Join Date
    Sep 2016
    Posts
    14
    Quote Originally Posted by The Dude View Post
    Time for an update:

    I finally got this thing done. I'm pretty sure I wouldn't do this again, at least to this level. But, I needed to make this right with this customer and he's a regular customer so......

    1) I ordered the module linked in post #30.

    2) I have a friend who is a fabricator. I asked him to make a bracket to replace the old heat sink. We often exchange favors. I mounted the new module on the replacement bracket. The idea was to get the heat sink of the new module directly in front of the existing fan.
    Attachment 45693
    Attachment 45694
    Attachment 45695

    3) I then re-mounted the old power supply/amp board to the bracket, of course with the STK gone.
    Attachment 45696

    4) I then had to move the whole assembly forward a bit as I still needed a bit more room to clear the fan, so new chassis holes.
    Attachment 45697

    5) Mount it up, wire it up, test.
    Attachment 45698

    I've been running it on the bench for a couple hours now and it's working great and heat sink cool to the touch at "normal listening levels". I don't expect that anybody would do this job for profit. The amp probably isn't worth the effort. It was kind of a fun project, so I thought I'd post the results. And I believe the amp is better than factory and certainly more reliable than using fake STK's. Thanks everyone for the help in this thread.

    P.S. If anybody else gets one of these modules, a connector for a CD drive fits right in the signal input connector of the new module. However, the ground pin is in the wrong spot so you have to pop the connector pins out and switch them around.
    I bought 2 of those Acoustic B200 amps very cheap and they both had the same problem. Blown STK404-140's. The reason they blow is because of those cheap junk capacitors. If you research TFY capacitors you won't come up with anything. When you crank the amp thats when things really go out of whack. I replaced every single electrolytic on the power board and never had any problems and I can crank the amps without any problems

  9. #44
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    Quote Originally Posted by PaulBass View Post
    I bought 2 of those Acoustic B200 amps very cheap and they both had the same problem. Blown STK404-140's. The reason they blow is because of those cheap junk capacitors. If you research TFY capacitors you won't come up with anything. When you crank the amp thats when things really go out of whack. I replaced every single electrolytic on the power board and never had any problems and I can crank the amps without any problems
    I wonder how a "cheap capacitor", can "kill an STK power module".

    Short ago somebody commented (was it Enzo?) that up to a couple years ago everybody asked "my amp blew, it is the transformer, isnīt it?" .... or the classic "I replaced all tubes and it still works bad" but lately everybody is betting on capacitors, no matter what.
    Juan Manuel Fahey

  10. #45
    Junior Member
    Join Date
    Sep 2016
    Posts
    14
    unstable power going to any component can cause it to malfunction or fail. In my opinion I don't think those cheap junk chinese capacitors have ever been tested and all the spec sheets are fake. when I yanked the caps from the B200's the ESR's were high. When I replaced them I noticed the slight 60Hz hum in one of the amps went away. If you use the amp at low volumes it probably won't matter but if you crank it up for gigs you're asking for trouble
    J M Fahey likes this.

  11. #46
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    30,402
    Weak filter caps cause increased hum. They can cause distortion as ripple modulates signal. Bad enough they lower the voltage in the supply. But I haven't figured out how they will cause the output stage to fail. I can see it making the circuit not work well, but I don't see it killing transistors.

    Just my opinion.
    Education is what you're left with after you have forgotten what you have learned.

  12. #47
    Junior Member
    Join Date
    Sep 2016
    Posts
    14
    not only the filter caps its every electrolytic in the amp. they are all chinese junk. I tested some of the film caps and they were in spec

  13. #48
    g1
    g1 is offline
    don't forget the joker g1's Avatar
    Join Date
    Feb 2010
    Location
    Canada, somewhere north of Fargo
    Posts
    9,884
    I'm not doubtful about the junk caps, I'm sure these are mass produced units that are replaced and not repaired.
    But it is also possible they are using cheap STK knock-offs in there that are blowing on their own and not because of the caps.
    If you replace the output device and all the caps and it works then that's great, but it doesn't necessarily follow that the caps were the cause of the failed output devices. I suppose it is possible, probably more so from output circuit caps than filter caps.
    Certified Dotard

  14. #49
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    And as Enzo often says, **how many** are actually blowing?

    Of course we get the bad ones on our benches, but 10 bad out 100 is appalling, same out of 5000 is excellent quality.

    As of "chinese junk" ... I guess nowadays thereīs nothing else on dealerīs shelves , and replacing OEM ones will most probably involve more chinese made ones.
    Juan Manuel Fahey

  15. #50
    Lifetime Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    30,402
    Plus I am still always interested in what is behind these claims. I would be perfectly happy to accept that bad caps blow up these output chips, but only if I am presented with some sort of reasoning behind HOW they do that.
    Education is what you're left with after you have forgotten what you have learned.

  16. #51
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,721
    Quote Originally Posted by Enzo View Post
    Plus I am still always interested in what is behind these claims. I would be perfectly happy to accept that bad caps blow up these output chips, but only if I am presented with some sort of reasoning behind HOW they do that.
    I have recently seen four cases high ESR caps in the feedback path lead to HF instability. The transistors were saved by virtue of the SMPS over current protection kicking in.
    Last edited by nickb; 12-17-2017 at 06:17 PM.
    Experience is something you get, just after you really needed it.

  17. #52
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,721
    Going back to the original subject. It occurred to me, rather belatedly, that a TDA7293 could be made to work as a substitute. The two biggest problems would be that the heatsink is connected to the -ve supply and so would require isolation and that they require a low thermal resistance to run at any power for any length of time.

    On a different tack, an odd thing is that these fakes took a great deal of effort to engineer. They have in injection moulded cover, a heatshink, a leadframe as well as the PCB. What a shame they apparently skimped on the all important transistor dissipation.
    The Dude likes this.
    Experience is something you get, just after you really needed it.

  18. #53
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    Close, but unfortunately no cigar.
    These Sanken modules are rated 120V or so, are happy with +/-52V rails, have large die power transistors (the real ones I mean, not the fakes) and have huge thermal contact surface to heatsink.

    TDA729x arenīt reliable beyond 45V rails and in fact are better restricted to +/- 42V or so, power chips are way smaller by necessity, not enough space, and contact surface is exactly 2 x TO220 packages side by side.

    They are simply not enough and explode trying to do their big brotherīs job.

    How do I know? ..... well, I tried anyway

    As a side note: LM3886 are known as very reliable, simply because they pull 50 or 60W RMS out of that puny package and succeed; TDA729x falsely claims 100W in the datasheet ... and punishes those who believe it.

    In my book, they are good up to 80W RMS, period, meaning +/-40V into 8 ohms load or +/-30V or so and 4 ohm load ... and then they work forever.

    But 100W RMS? "optimistic" is the understatement of the Year.
    nickb likes this.
    Juan Manuel Fahey

  19. #54
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,721
    Quote Originally Posted by J M Fahey View Post
    Close, but unfortunately no cigar.
    These Sanken modules are rated 120V or so, are happy with +/-52V rails, have large die power transistors (the real ones I mean, not the fakes) and have huge thermal contact surface to heatsink.

    TDA729x arenīt reliable beyond 45V rails and in fact are better restricted to +/- 42V or so, power chips are way smaller by necessity, not enough space, and contact surface is exactly 2 x TO220 packages side by side.

    They are simply not enough and explode trying to do their big brotherīs job.

    How do I know? ..... well, I tried anyway

    As a side note: LM3886 are known as very reliable, simply because they pull 50 or 60W RMS out of that puny package and succeed; TDA729x falsely claims 100W in the datasheet ... and punishes those who believe it.

    In my book, they are good up to 80W RMS, period, meaning +/-40V into 8 ohms load or +/-30V or so and 4 ohm load ... and then they work forever.

    But 100W RMS? "optimistic" is the understatement of the Year.
    Luckily, I never liked cigars anyway. Never understood what the pleasure was in them.

    The TDA would only be a candidate to replace the lowest power 70W version. You could mount two operating in a bridged or parallel for more power (lower out Z). That will get you the power but it doesn't solve the supply voltage issue and the replacement would need to be compatible.
    J M Fahey likes this.
    Experience is something you get, just after you really needed it.

  20. #55
    Junior Member
    Join Date
    Sep 2016
    Posts
    14
    Quote Originally Posted by g1 View Post
    I'm not doubtful about the junk caps, I'm sure these are mass produced units that are replaced and not repaired.
    But it is also possible they are using cheap STK knock-offs in there that are blowing on their own and not because of the caps.
    If you replace the output device and all the caps and it works then that's great, but it doesn't necessarily follow that the caps were the cause of the failed output devices. I suppose it is possible, probably more so from output circuit caps than filter caps.
    Is there a way to tell if the STK's were knock offs? They looked legit to me. They looked exactly like the ones I yanked out. I bought them from a reputable US seller

  21. #56
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    5,390
    That's kind of what the thread is about. Start at post 1. There's not really a way to tell unless you crack one apart. The originals are no longer in production, so most all of them are fakes.
    J M Fahey likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  22. #57
    Old Timer J M Fahey's Avatar
    Join Date
    Oct 2007
    Location
    Buenos Aires, Argentina
    Posts
    10,176
    True.

    That said, "another" semiconductor maker *might* make a good quality copy and corner a small but still interesting niche market, thereīs tens of thousands (if not Millions) STK modules out there.

    No need to be a *full* manufacturer, meaning no need to grow NASA technology own crystals, most large manufacturers sell unmounted dies in bulk for the power transistors and the rest is just an SMT circuit, easy peasy and cheap nowadays.

    If I were a young Engineer in China and wanted to start up something with a few friends I would consider it.

    Back to the one you bought, only actual use can prove what you have.
    Juan Manuel Fahey

  23. #58
    Senior Member
    Join Date
    Dec 2011
    Location
    Pretoria, South Africa
    Posts
    673
    JM Fahey.
    Please share your design and pcb if possible.
    Last edited by diydidi; 01-28-2018 at 03:07 PM.

  24. #59
    "Thermionic Apocalypse" -JT nickb's Avatar
    Join Date
    Dec 2009
    Location
    Devon, UK
    Posts
    2,721
    diydidi: Edit your port to remove your email address (unless you like spam).
    Experience is something you get, just after you really needed it.

Page 2 of 2 FirstFirst 12

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. STK404-140
    By lowell in forum Maintenance, Troubleshooting & Repair
    Replies: 9
    Last Post: 01-09-2017, 11:52 PM
  2. Replies: 1
    Last Post: 02-12-2011, 07:31 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •