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Build STK8050 equivalent
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Old 21st February 2018, 06:32 PM   #1
Depaj is offline Depaj  France
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Default Build STK8050 equivalent

Hi,

A friend got me his two Technics SU-V4 amps, both have failed STK modules. I've been reading a lot of bad stuff about those and even worse about the modern counterfeit ones you can buy of a lot of sites.
He really wants to save his amps and I was wondering if it wouldn't be possible to build an equivalent to the modules circuit with discrete components. It seems to have been done for other references (stk-0050 is one of them I believe).
Is it possible to just copy the schematic of the internal circuitry of the stk by using discrete components that can handle a lot more to prevent getting the same problems all over again ?
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Old 21st February 2018, 06:59 PM   #2
anatech is online now anatech  Canada
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Build STK8050 equivalent
Hi Depaj,
You might be further ahead adapting another chip to work. Have you checked to see if those chips are available from Panasonic / Technics? If they are, buy them and treat the amplifiers a little more nicely. Failing that, use the chip from one to make the other play again.

If he's going to run the amplifiers hard (they are not suited to that use at all), then buy amplifiers that can handle it. Yamaha Pro amps are extremely good. Old BGW-750 B or C can sound good after a rebuild.

If he has his equipment stacked, he can't do that. Each amp should have 4"~6" clear air above. More if he has it up loud. This is true of all amplifiers.

If he really wants loud, then buy a Carver M-1.5t. That will finish his speakers and his hearing. I think that one is a real 375 wpc.

I can't really offer you any better advice. He has to come to understand these amplifiers are not suited to running at high power, and certainly not stacked as the advertising pictures show.

-Chris
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Old 21st February 2018, 08:32 PM   #3
Depaj is offline Depaj  France
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Hi Anatech,

A different STK you mean that can handle a little more power to be safe ? The original modules were made by Sanyo apparently but they have been discontinued for a long time and it got almost impossible to get genuine ones. The fake ones tend to fail even with lower bias currents and clamp voltages at moderate volume so...

I don't think he really runs them very hard but I'm sure he's not looking to buy a new amp.
I know I always advice to give any amplifier some room to breathe and I know for sure he does that as well.

A lot of people seem to be trying to save these amps and get confronted with the same problems, wouldn't it be worth the trouble to try and find a solution. I know these aren't the greatest models but I don't think they deserve to just all be thrown away.
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Old 21st February 2018, 08:56 PM   #4
SVI2004A is offline SVI2004A  New Zealand
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Build STK8050 equivalent
I have a V4 that has a dead STK - I am considering replacing both with a STK2058IV or SVI2004 power IC, which would retain new class A operation with much less external throughput pins.

See attached pics

Might consider replacing current stabiliser transistors with resistors - as seen in last pic
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Old 21st February 2018, 09:33 PM   #5
Depaj is offline Depaj  France
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Hi SVI2004A (seems you kind of like this one)

None of these seem to be drop in replacements and they are both 2channel devices, there would have to be some serious re-routing on the board right ? Also what happens to the clamp voltage adjustment ? Is there any guarantee that buying these will get me genuine parts ?

The stk2058IV seem very expensive, is there a guarantee that the SVI2004
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Old 21st February 2018, 10:15 PM   #6
anatech is online now anatech  Canada
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Hi Depaj,
Mount the new IC to it's own PCB and make the connections between that and the main PCB. Easy-peesy. Either that, or scrap them. You don't have many options.

Don't assume anything that your friend knows or does. Always ask to make sure. There is a reason he has two dead amplifiers. Design is one because they allow those chips to run pretty warm. The fan is very ineffective as well, blowing directly onto the side of the heat sink.

I'm afraid there is no cheap way out of this. So the question now becomes, how much dies he want to keep those amplifiers?

-Chris
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Old 21st February 2018, 10:23 PM   #7
Depaj is offline Depaj  France
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I should of said right away "I know because I asked him", they are on top of a table with nothing above. There actually isn't any fan in this model, sure you aren't mistaking it for the SU-V4X ?

Well it would seem he got really attached to them, sometimes you just can't explain it.

I might be optimistic here but I really don't see why it wouldn't be possible to rebuild the damn stk with discrete components, I would need the values of the resistors and some equivalents for the transistors, Is it possible for someone more experienced than me to get those with an ltspice model ?
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Old 22nd February 2018, 12:11 AM   #8
jaycee is offline jaycee  United Kingdom
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I've often wondered about building the STK modules which are just the frontend/voltage amp stages using surface mount parts on an ordinary PCB. Should be perfectly doable i guess.
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Old 22nd February 2018, 12:14 AM   #9
globalplayer is offline globalplayer  Germany
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I think you could do better than those STK-ICs.
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Old 22nd February 2018, 01:59 AM   #10
SVI2004A is offline SVI2004A  New Zealand
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Quote:
Originally Posted by anatech View Post
Hi Depaj,
Mount the new IC to it's own PCB and make the connections between that and the main PCB. Easy-peesy. Either that, or scrap them. You don't have many options.

Don't assume anything that your friend knows or does. Always ask to make sure. There is a reason he has two dead amplifiers. Design is one because they allow those chips to run pretty warm. The fan is very ineffective as well, blowing directly onto the side of the heat sink.

I'm afraid there is no cheap way out of this. So the question now becomes, how much dies he want to keep those amplifiers?

-Chris
True... in this case I must say STK8050s do drop for no reason at all... I have a few amps that have done this without ever leaving low volume.

As for clamp V, this is fixed internal in the stereo power packs as is Icq... which is why Id look into the the 2 3.9K resistor array which will ensure optimal constant current.
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