STK404-140S Question

[Jazz P Bass]

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

[The Dude]

The supply in this Acoustic amp is +-52V. That's part of the reason I was looking at this particular amp.

[J M Fahey]

It looks good, personally Iīd 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, Itīs 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?

[The Dude]

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!

[The Dude]

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.




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


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.


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


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.

[J M Fahey]

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.

[The Dude]

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]

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

[glebert]

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.

[The Dude]

Yes. And, it's repairable at component level. Once you've retrofitted it, you're good to go.

[nickb]

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:

[J M Fahey]

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:

[PaulBass]

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.
[ATTACH=CONFIG]45693[/ATTACH]
[ATTACH=CONFIG]45694[/ATTACH]
[ATTACH=CONFIG]45695[/ATTACH]

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

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.
[ATTACH=CONFIG]45697[/ATTACH]

5) Mount it up, wire it up, test.
[ATTACH=CONFIG]45698[/ATTACH]

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

[J M Fahey]

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.

[PaulBass]

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