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Thread: STK404-140S Question

  1. #1
    Supporting Member The Dude's Avatar
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    STK404-140S Question

    I'm just curios if anyone has enough experience with these things to tell me whether this might be a counterfeit or not. It was purchased as "Original Sanyo". I'm having serious doubts if that's true. Looking at the actual output devices within the part (on the heat sinks), they look substantially smaller than the ones from an original part and it seems suspect to me. I could certainly be wrong. It's been a while since I cracked one of these open. The reason I ask is because this is the second failure in this amp- both times the STK was replaced. The IC's for each repair came from different vendors. I want to make sure I get a "real" part next time, if that's even possible. I'm thinking NOS versions of these are rare as hen's teeth. BTW, the amp is the GC Acoustic B200H.
    For your viewing pleasure:

    stk404-140s.jpg
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    “Yeah, well, you know, that’s just, like, your opinion, man.”

  2. #2
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Wow! I'm really impressed that you got it open so cleanly and with no damage Do tell how you did it....

    I did fit one of these to VOX about 6 months back. No reports of failure so far but I was highly sceptical about the originality. I bought a spare and now I'm tempted to do what you just did.

    Do those output transistors bond directly to the heatsink?
    Experience is something you get, just after you really needed it.

  3. #3
    Old Timer J M Fahey's Avatar
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    **Usually** fake transistor chips are covered in the infamous white epoxy.This is your presumed fake:


    Maybe they think it cools them better because "it´s a white paste"? Only half kidding here ... or not at all
    Tech removed one white blob showing a die too small fo intended power.
    I get mad because if they used just a slightly larger die in an otherwise complex circuit, it would actually work.
    Who cares who actually made it as long as it works?


    Fake:


    Original (no epoxy of any kind hiding power chips):


    Fake:


    Some go to heroic levels to repair them:
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    Juan Manuel Fahey

  4. #4
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nickb View Post
    Wow! I'm really impressed that you got it open so cleanly and with no damage Do tell how you did it....
    They are not actually potted or gooped but just a real discrete power amp, built on a conventional PCB, with a plastic cover over them.
    Juan Manuel Fahey

  5. #5
    "Thermionic Apocalypse" -JT nickb's Avatar
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    You could have played me for a bit there

    I took a look at the ones I have and see that what you say is true. I kept the original so I could lift the lids on both it and the copy but I think you have already answered the OP , so Dude, yell if you want me to do it.
    Experience is something you get, just after you really needed it.

  6. #6
    Supporting Member The Dude's Avatar
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    Thanks for the comments, guys. I suspected it was fake, but.......
    Nick, to get the thing cracked apart, I set it legs up on the bench, leaned it against something to keep it from tipping over, inserted a small screw driver next to the legs on each side and gently whacked it with a hammer until it started coming apart. I then pried it the rest of the way. If you could crack open a known original part, I'd love to see the difference. My recollection is that the output devices were larger last time I opened one. It would be nice to confirm and I no longer have the original part. That said, don't put yourself through too much trouble on my account.
    My next problem is finding a "real" part to fix this thing once and for all. If I can't repair it with confidence, I might just refund and bail on the amp.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  7. #7
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Here it is. BTW this was an STK404-130




    Busted transistor:


    stk404-real.jpgwin_20170927_09_01_22_pro.jpg
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    Experience is something you get, just after you really needed it.

  8. #8
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Agee Juan. Also, if they were upfront and said something like "new design compatible replacement for STK4XX made with current techniques" then everyone would be happy.
    Experience is something you get, just after you really needed it.

  9. #9
    Old Timer J M Fahey's Avatar
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    Just as a "Plan Z" , please post a couple gut pictures of that amp, a general view and the power amp/heatsink area.
    Since they reproduced the aesthetics of the late 70`s ACOUSTIC amps,that chassis should be roomy and half empty.
    Also post rail voltages.
    Plan Z might involve mounting a cheap simple power module inside that chassis, attached to old heatsinks and fed from original supply.
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    Juan Manuel Fahey

  10. #10
    Supporting Member The Dude's Avatar
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    Oh, there's plenty of room in the chassis. Here's a picture. I'll get some voltage measurements as soon as I have time to get back into the thing. I had thought about mounting another power module in there. That may be an option. I'll have to see what the customer wants to do.

    ampeg-b200h.jpg

    Edit: Forgot, thanks for posting the pics Nick!
    Last edited by The Dude; 09-28-2017 at 02:34 AM.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  11. #11
    Old Timer J M Fahey's Avatar
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    Just looked at your amp: you have lots of space BUT Power Amp PCB also contains main power supply (so far no big deal) but also low voltage supplies, Fan supply, DC protection, etc.

    You might still add an external module, only pull strictly power amp parts, just to put them out of the way, and wire the 5 basic connections to new power module: IN / OUT / +V / -V / Ground
    Amp will work (as in: amplify and drive speakers) but will lack some functions, specilly protections.

    Keep looking at the STK module and it´s really a packaged (not even encapsulated) discrete power amp, and as such .... "repairable".

    Given it uses power Darlingtons and resistors are external, I wouldn´t be surprised to find that only them are dead and other parts are functional.

    If I had free time, and just out of curiosity, I´d grab a couple power Darlingtons (even humble TIP142/147, but in that case use a lower supply, say +/-40V or less) and try this brain surgery:

    stk404-to247.jpg

    If I ain´t wrong, left one should be PNP and right one NPN .

    That said, I found a UK supplier who claims to have STK:
    https://www.express-elect.com/about.php
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    Juan Manuel Fahey

  12. #12
    Supporting Member The Dude's Avatar
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    Yep. The power supply and power amp are indeed on the same board. That said, I think I could still install a power amp module and just use the existing supply. Leaving the STK out should, as you say, "pull strictly power amp parts" since the STK basically is the power amp. I actually checked out the STK after I popped it apart and it's not just the outputs that are shorted. Drivers are also toast and there are some burnt resistors. I'll update after I check to see what rail voltages are and thanks for your help!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  13. #13
    Old Timer J M Fahey's Avatar
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    As you already know, I don´t care too much about tube (slightly bored about the same old 4 or 5 recipes on the menu, repeated over and over and over and over) and on the contrary am a sucker for SS design ... and that amp reeked of Rick Kukulis´ hand (every designer has some pet ideas which he uses wherever he can) and on a hunch checked his designs: that "Acoustic" amp is actually a (modern) Kustom.
    To be more precise, the KBA115C/210C .
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    Juan Manuel Fahey

  14. #14
    Supporting Member The Dude's Avatar
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    Thanks Juan! At least I now have a schematic that's close!
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  15. #15
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    Dumb question, but would Acoustic (or perhaps Kustom) sell replacements for this IC? I know Kustom offered to sell me a reverb tank for my Kustom Defender V100 amp (which I still haven't gotten around to finishing..).
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  16. #16
    Old Timer J M Fahey's Avatar
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    Worth asking.
    Amp is made in China, but they should have a small stock of parts in USA for warranty repairs.
    I also found suppliers offering the 140-N version, made by ON , which is more likely to be true, than unavailable for years Sanyo. (140-S)
    All are pin compatible.

    Pity Mouser/Digikey/Futurlec which presumably can be trusted, show "out of stock".

    JPBass had kindly uploaded this schematic: http://music-electronics-forum.com/a...ustic-b200.zip
    Juan Manuel Fahey

  17. #17
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    What is funny is that I can buy STK404-140S in Poland for about $15. But, taking into account my latest adventures with fake 2SC5200 transistors, I wouldn't trust that they are original.
    Here is a schematic of the module but at first glance it does not match your board.
    stk404.jpg

    You can always try to buy it from OnSemi: http://www.onsemi.com/PowerSolutions...=STK404-140N-E

    Mark

  18. #18
    Supporting Member Jazz P Bass's Avatar
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    The On Semi 140N-E works as a replacement.

  19. #19
    Supporting Member The Dude's Avatar
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    The manufacturer no longer supports this amp. In fact, from what I can glean from several web searches, because of IC failures and part availability, they redesigned the amp with an output section built from discreet components and called it the Mark II. All of this is unverified. I'm currently investigating the prospect of getting a Mark II power supply/output module for the amp (if what I read is indeed true). I'm aware that the On Semi 140N-E would work as well, but those are also apparently discontinued and it'd be a crap shoot as to whether you are getting fakes or not if you could find them.
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  20. #20
    Old Timer J M Fahey's Avatar
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    Try to get that.
    If impossible, and you don´t mind getting your hands dirty making a small laser transfer PCB, I can send you the design of a simple general purpose one I use for "unrepairables".
    Fed and cooled by original supply and heatsink.
    Just how much free space do you have between PCB and top edge of heatsink?
    You will probably have to redrill it to accomodate a pair TO247 transistors, which provide the muscle.
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    Juan Manuel Fahey

  21. #21
    Supporting Member The Dude's Avatar
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    Thanks for pointing out the schematic link, Juan and thanks JPB for uploading it.
    FWIW: The schematic shows the rail voltages at +&-52 for the STK IC and of course the obligatory +&-15 for the op amps. If need be and the customer agrees, I should be able to find a replacement amp module to install. But, I'm first waiting to hear back from Acoustic to see if they have something already built for this chassis and how much they want to soak me for it.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  22. #22
    Supporting Member The Dude's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Try to get that.
    If impossible, and you don´t mind getting your hands dirty making a small laser transfer PCB, I can send you the design of a simple general purpose one I use for "unrepairables".
    Fed and cooled by original supply and heatsink.
    Just how much free space do you have between PCB and top edge of heatsink?
    You will probably have to redrill it to accomodate a pair TO247 transistors, which provide the muscle.
    There is about 2 inches from PCB to top of heatsink. If I can't get something from Acoustic, I may well take you up on your design. I don't mind getting my hands dirty at all. I'd much rather have the TO247's than trust another STK!
    J M Fahey likes this.
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  23. #23
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    Quote Originally Posted by The Dude View Post
    Thanks for pointing out the schematic link, Juan and thanks JPB for uploading it.
    FWIW: The schematic shows the rail voltages at +&-52 for the STK IC and of course the obligatory +&-15 for the op amps. If need be and the customer agrees, I should be able to find a replacement amp module to install. But, I'm first waiting to hear back from Acoustic to see if they have something already built for this chassis and how much they want to soak me for it.
    There are some class D power amp modules on Ebay for less than $20 that work on 35-55V. Can't be much less reliable than the fake Sanyo parts. I'm thinking of getting one and putting it into a failed Gallien Krueger 400B that is vexing me. I could maybe even use the 500W module....
    Last edited by glebert; 09-29-2017 at 04:11 AM.
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  24. #24
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by glebert View Post
    There are some class D power amp modules on Ebay for less than $20 that work on 35-55V. Can't be much less reliable than the fake Sanyo parts. I'm thinking of getting one and putting it into a failed Gallien Krueger 400B that is vexing me. I could maybe even use the 500W module....
    I've bought and used a 100W class D module from that source based on a TDA7492. No complaints from customer do I guess it's still going. Also consider the 100W TDA7293 modules from the same source that will take AC or DC and go for under $4.00 (!!!).
    Last edited by nickb; 09-29-2017 at 06:27 PM.
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  25. #25
    Supporting Member Jazz P Bass's Avatar
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    Can you link the 'source' for the Class D modules?

  26. #26
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    Can you link the 'source' for the Class D modules?
    only $6.30

    2 x 50W TDA7492 D Class High-Power Digital Amplifier Board AMP Board+ Radiator | eBay

    You run the outputs bridged to get 100W, although 80W is more realistic expectation IMHO.
    Last edited by nickb; 09-29-2017 at 07:08 PM.
    Experience is something you get, just after you really needed it.

  27. #27
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    If you just search in ebay for "class D module" you will find lots of different options. You can add "mono" or "stereo" depending on what you want. I've seen 500W, 250W mono boards, at 100W and below they seem to go to stereo modules. Supposedly the bigger modules can also be run half-bridge to link two modules for double the power but I don't know that I want to do kW amps with ebay parts just yet.
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  28. #28
    Supporting Member The Dude's Avatar
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    Well I just heard back from Acoustic.

    "Unfortunately we don't carry any parts for our amps. Typically if we have a customer that is having issues with their amp we just have them replace the whole thing with the retailer they purchased it from since we don't have access to parts that we can get out to technicians."

    I'll be having a conversation with the customer to see how he wants to proceed.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  29. #29
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by The Dude View Post
    "Unfortunately we don't carry any parts for our amps. Typically if we have a customer that is having issues with their amp we just have them replace the whole thing with the retailer they purchased it from since we don't have access to parts that we can get out to technicians."
    Meaning: "we have no clue, we didn´t even design it, can´t even read a schematic. We´re just a bunch of [insert University name here] Business School graduates who created a new Company, bought Acoustic name because it was available and reasonably priced, got a few investors and found this wonderful Chinese Company which takes care of the dirty details"
    Disclaimer:
    "Any similarity to living or dead persons is not a coincidence"
    Oh well
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  30. #30
    Supporting Member The Dude's Avatar
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    Any comments on this?

    IRS2092 CLASS D Audio Receiver Power Amplifier AMP Kit 200W MONO Assembled Board | eBay

    It will fit physically. Reviews that I can find seem good. Specs seem like it will work with my existing supply. Price is right. I'm just a bit leery of more fake Chinese crap. I'm wondering if anyone has tried such things and if so what the results were.

    Juan,
    I've also PM'd you in regards to post #20.
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  31. #31
    Supporting Member Jazz P Bass's Avatar
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    Not much description on that page.

    This same amp shows requiring a 50Vdc supply.
    IRS2092 CLASS D Audio Receiver Power Amplifier AMP Kit 200W MONO Assembled Board

    I have used this one (32Vdc supply) to redo a Bang & Ulfson Ice power module.
    http://vi.vipr.ebaydesc.com/ws/eBayI...1&secureDesc=1

  32. #32
    Supporting Member The Dude's Avatar
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    The supply in this Acoustic amp is +-52V. That's part of the reason I was looking at this particular amp.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  33. #33
    Old Timer J M Fahey's Avatar
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    It looks good, personally I´d order one, if anything to test and have it availble as a backup/replacement board.

    Given the current crop of Obsolete IC/fakes/Unrepairable Class D/proprietary modules amps we are finding everywhere, It´s interesting to have an "Acme brand" multipurpose module.

    After all, more and more amps are coming as "DNR/replace only/full board replace" straight as the "official" Factory suggestion, so ... what can we do?
    Juan Manuel Fahey

  34. #34
    Supporting Member The Dude's Avatar
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    Well, I ordered one. We'll see how it goes. If it doesn't work out, I'll be contacting you again, Juan. Thanks everyone for your help!
    J M Fahey likes this.
    “Yeah, well, you know, that’s just, like, your opinion, man.”

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