TA-200W replacement (Kenwood KR-9600)

I finally got around to fixing a friend's Kenwood - I haven't done a power amp project since college (guess how many years ago !). It turned out ok. I'll be glad to supply details if anyone else needs one of these.
 

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Here's the schematic - very simple. Outputs are darlingtons, the bias diodes are included in the package. Rbias could be 200 ohm trimpot, typically ends up in 10-30 ohm range. The outputs are mounted on the back of the board against the heatsink. The 330pf caps probably compensate for the airwiring. And I know the circuit is a little over-protected.
Prototype 1 used the SAP15 transistors which include the emitter resistors - but the SAPs are out of production. Prototype 2 used parallel pairs of STDs, but stability, or rather docility, was an issue - probably due to wiring.
Funny, it's been 40 years since I've done any power amp work (other than repairs) and very little has changed.
Even funnier, the pad that I used to jot down the rough schematic is the same one I used in college - 40 years ago !
I've included a schematic of the KR-9600 output board, but it's a bit hazy. Anyway, pins 1 & 10 are power, pins 3 & 8 are drive, 5 is output, 6 is ground.
 

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Here's a (maybe) better Kenwood schematic.

Hi alhaynes, your TA-200W replacement looks interesting. I am working on one I just bought which does not yet have bad outputs but it's good to know you have a cure.

There is no DC zero adjustment on the original power amp and my unit is running 150mV on L and 160mV on R. I'm thinking that is a little too high. Do you have any thoughts on curing that, and what were you able to achieve on your circuit?

Thanks
 
Did anyone hear back from alhaynes...?

Wondering if anyone heard back a reply to their inquiries/posts from alhaynes??? I know that this is an old thread, but I would venture to say to there are a few KR9600's out there. Like anything electronic, they aren't going to last forever! And, judging from what I have heard, those power paks do take a licking during startups...

I have a Kenwood KR9600 (original owner) that I am currently using as a main amp (bypassing the pre section) in my main hifi system. I am close to finishing up a Nelson Pass clone F5 Turbo DIY project that will replace the Kenwood, at least temporarily.

The aging Kenwood needs some phono amp section work. I plan on going in and tinkering to see what is possibly wrong (no output on one channel when using phono section; all other preamp sections work great). I figure since I have it apart, I might as well rebuild it with modern caps/resistors, etc. I would especially be interested in a BOM for the replacement/rebuild.

It would be great to have further insight into the Darlington power paks which, as I understand it, are no longer available.

Any guidance from more experienced Darlington array/Kenwood gurus would be greatly appreciated.
 
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Here's the schematic - very simple. Outputs are darlingtons, the bias diodes are included in the package. Rbias could be 200 ohm trimpot, typically ends up in 10-30 ohm range. The outputs are mounted on the back of the board against the heatsink. The 330pf caps probably compensate for the airwiring. And I know the circuit is a little over-protected.
Prototype 1 used the SAP15 transistors which include the emitter resistors - but the SAPs are out of production. Prototype 2 used parallel pairs of STDs, but stability, or rather docility, was an issue - probably due to wiring.
Funny, it's been 40 years since I've done any power amp work (other than repairs) and very little has changed.
Even funnier, the pad that I used to jot down the rough schematic is the same one I used in college - 40 years ago !
I've included a schematic of the KR-9600 output board, but it's a bit hazy. Anyway, pins 1 & 10 are power, pins 3 & 8 are drive, 5 is output, 6 is ground.


STD03N and STD03P you used - and you have the diode and cap circled along with the transistor. Is that cos its included in the transistor already ?

And why is the circuit board on the heat sink and not the transistor ? Is that just for fit ?

Thanks.
Srinath.
 
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I've seen these devices used before. Two output devices leave precious little room for oddball phase angles. I'd not consider this a very 'robust' modification, though it will bring the unit back to life (at least until a difficult speaker is connected, or someone gets too frisky with the volume control).
 
I would almost bet the family farm that Kenwood in Japan has the original specs and additional info on their original power packs. The problem is that one would have to be able to speak Japanese in order to email that request and read the responses. I would think that they would want these vintage units from HiFi's golden age to continue to survive and thrive.

Of course, there is always the slim possibility that there are some techs out there that used to work for Kenwood that could provide us with some guidance. I know that in the late 70's one of my KR9600 power packs failed and I took it to Kenwood's suburban Los Angeles service center. They replaced the pack, serviced the unit, spec'd it out--all at no charge! How is that for old-fashion service! Not very many companies out there today that will provide customer service like that, nowadays.

On the other end of this customer service spectrum, I requested a good service facility for a Theta Digital DAC from the company's headquarters in Los Angeles recently and they DID NOT EVEN RESPOND BACK! Am I ever going to buy any Theta Digital products in the future? I think NOT!
 
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We are in a use and throw and most importantly buy more culture.
They don't even care, we are the sheeple. You wont buy a theta, you may buy a parasound. The ones disappointed in parasound are Theta's next round of customers.
We need to buy nothing, and fish em out of scrap piles and repair and use ...

The greenest car isn't one you already own, its one you have pulled out of the junkyard.

Cool.
Srinath.