B&K ST-202 refresh and upgrade

gmcman

Looking to take this amp up a notch or two, not sure how to go about this other than recapping and maybe replacing some resistors, perhaps the ceramics in the transistor boards...not sure.

Only date I see in etched into the board dates back to 1990, no doubt it has some miles on it. The amp works, not sure the size of the power supply, the big caps measure 14,400uf and are rated at 15,600.

If anyone has done one of these please chime in. Looks fairly easy to work around and not a whole lot of components. I don't think I can turn it into a Krell or a McCormack but I would like to drive the 2.3TL's with more clarity and detail than my 200.2 provides which is still a fine amp but there's always room for improvement.

I assume the transistors are good, not so sure about the ceramic resistors, maybe they give the warm sound.....not sure

All input appreciated.


Here's some pics.

tonyb

Can't help ya, but I will comment that for a 26 year old amp, those caps look pretty good. All of the guts look good actually.....and pretty clean to boot.

Not so sure I'd roll the dice on spending the coin for new caps and resistors. If you sell the amp, add what you might spend on upgrades, you might be able to buy a used McCormack or older Krell.

More clarity and detail is what your after eh, your sure it's the amp and not something else in the chain ?

gmcman

tonyb wrote: »

More clarity and detail is what your after eh, your sure it's the amp and not something else in the chain ?

That's a fair assumption.

I figure the amp is good and the rest is up to par, but I'm willing to bet the B&K 200.2 while being a great amp, surely can't be the last word in detail. Maybe I need to spend some big $$$ to get above that threshold but I'm willing to take the gamble.

I've read about some ST-140's and 202's that really shine when modded but how they were modded I don't know.

Nightfall

Check this out

http://www.musicaldesign.com/MC_BK_Amp_Mods.html

gmcman

Nightfall wrote: »

Check this out

http://www.musicaldesign.com/MC_BK_Amp_Mods.html

Ironically I just got off the phone with John, thanks for the link though. I could get this fully done up for about $900-1K, whole enchilada.

There are a lot of amps for $1K, but people seem to rave about his mods....tough call.

heiney9

26 year old amps need refreshing no matter how visually pleasing it looks inside. Have you checked at DIYAudio.com or done a 'net search to see if anyone has any info.

A schematic will go a long to helping see what parts are in the signal path.

Modern rectifiers can make a big difference in sound. Perhaps look into that.

I think you will have a hard time finding the exact fit for those big cans. Those have fallen out of favor and multiple, smaller caps in a modern power supply are what you see now. For example my Aleph 30 has (10) 12,000uF caps in the power supply. A total capacitance of 120,000uF

Just my .02c

H9

P.s I did get your PM and I will respond when I have time to give you a thorough response. Heading out the door at the moment.

FTGV

First and foremost it would be prudent to verify that there is no potential speaker damaging DC voltage at the outputs,and that bias set to spec. You'll need to find a service manual.I will take a look online and see if I can find one.

What does the $1k mod include? Hopefully more than just a cap swap. There are not a lot of electrolytics and I only see a few films.In fact just from the overall component count it looks to be a reasonably simple circuit,which is typical of MOS FET designs. ( Also I see there is no sign of any components being thermally stressed which is a good thing).I have no experience with them but my understanding is that these B&K MOSFET designs had a soft and warm character about them.Since this sonic DNA is in the circuit design you may hear improvements but I have my doubts a simple passive parts upgrade will make them hi resolution champs.

As for the big filter caps, while they may have a lot of hours on them that doesn't necessarily mean they are at the end of their useful life. Depending upon working temp and voltage some of these old cans can last 30+ yrs. A check of their ESR's would be needed. While harder to source new screw terminal types they can be found, just be prepared to open your wallet. If you want to upgrade to modern PC board mounted types you will have to find an alternative way to mount them and provide support for the main circuit board.Since it appears to be held in place by the filter caps.
I like the simple mechanical design.It looks very tech friendly,easy to assemble and diassemble for servicing or modding.

gmcman

The warm sound is fine, I guess I'm looking for more of a fresh amp and cleaner sound. The mods are more than caps, but I'm thinking this will turn into a total amp upgrade than a modification.....seems hard to ignore the fact I can get a used McCormack DNA.5 for about 2/3 the price of an upgrade to an older amp.

So that's my second dilemma, been looking at the DNA .5 and .125 for the 2.3 TL's, also considering the Parasound 2250 V2 or maybe the A23. Would the McCormack's be enough for the 2.3's or should I push for more wattage?

Mike Reeter

The A23 would definitely run the 2.3's, but not as well as an A21. Years ago I had a Parasound HCA-1500 and a HCA-1000 in a bi-amp configuration on a pair of 2.3TL's and they sounded very good.

You should be able to find a good used A21 for around $14-1700. Parasound and SDA's are a very good match up as you know.

SCompRacer

FTGV wrote: »

If you want to upgrade to modern PC board mounted types you will have to find an alternative way to mount them and provide support for the main circuit board.Since it appears to be held in place by the filter caps.

I had an active crossover bass amp where they removed four 10,000uf big caps (lots of capacitance!) to make room for the active circuitry. (The same design panel amp without active xover had 80,000uf).

Fred suggested this, numerous smaller caps instead of trying to add additional big can caps. I was able to increase capacitance to near 80,000uf for the bass amp this way. Long standoffs were ordered and installed to support the boards (so I could remove the temporary paper cups support).



Before, just 20,000uf per channel. The same design panel amp had two additional caps per side behind these.

FTGV

I forgot about that one Rich.Looks rather menacing.In stock form has similar layout as the B&K.

motorhead43026

I am going to have Musicaldesign/Concepts, mod/refresh my Hafler XL600 next year.

FTGV

motorhead43026 wrote: »

I am going to have Musicaldesign mod/refresh my Hafler XL600 next year.

That's a beast of an amp.It could also be used as an arc welder.

SCompRacer

I like beastly amps!

gmcman

tonyb wrote: »

More clarity and detail is what your after eh, your sure it's the amp and not something else in the chain ?

That's always a possibility and definitely worth exploring. The ST-202 isn't currently my main 2CH amp, that duty is assigned to the 200.2 and those two amps are surely different with everything else being equal, the 200.2 just works and sounds better with the 2B's likely with the higher current it can provide as well as more refined.

SCompRacer wrote: »

Before, just 20,000uf per channel. The same design panel amp had two additional caps per side behind these.

That's quite an upgrade.....very nice.