Krell KSA 250 - The Mother Clone !!!

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#2
Ok, Just to update, I have just found another Krell KSA-250 Amplifier for sale, but this one is in Canada, also in working condition and this one is going for $ 2300 .. so we have one more new option !! Yes, this is getting beter ..

Ok, I just want to clear a few things up for now ..

I think the best idea is that we find the users that are the closest together with the most knowledge and ship the amplifier to those users to dis-assemble .. that way there is more security for everyone !

Also, does anyone know of any more Krell KSA-250's going for good prices ? .. the better price we find .. the quicker we can get to work !
 
#4
Of course you are free to deconstruct any piece of kit out there, but you are not allowed to publish any copyright material here. So you can draw up your own schematic and pcb, but not post anything that infringes Krell's IP, so you can't use their board artwork for example.
 
#5
@pinkmouse

Ok, 🙂 thanks for that info ! .. I don't plan on publishing anything 🙂 but I know there are quite a few people that want schematic information or even the real thing ! .. so I guess it will be an effort closed to the participating users 🙂 after all .. I don't want anyone to get into trouble ..

I do plan on .. lets say "borrowing" ideas from it then, and I will 🙂 ..

@Jozua: Ok, that is one thing to keep in mind .. I hope that I can get enough willing people ..
 
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#9
I own a KSA-250 and plan on doing a full teardown and rebuild of it this winter. I am interested in this project and might be able to supply info and photos as i tear mine down. I am hoping I can derive a schematic!

It is my understanding there are 3 versions of this amp! so if you plan on buying one, you will have to first decide what generation of 250 to buy!
 
#10
Zero Cool said:
I own a KSA-250 and plan on doing a full teardown and rebuild of it this winter. I am interested in this project and might be able to supply info and photos as i tear mine down. I am hoping I can derive a schematic!
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I rebuilt two KSA250s several years ago. They still are in daily operation behind Apogee Full Range Speakers. I spent about $600 in replacement parts for each amp. I have a large workbench with both compressed air and a powerful vacuum, as well as several different solder/de-solder stations. It took me 16 hours(1 weekend) to clean and rebuild each stereo amp(8hrs work, 8hrs confusion). It took me 1 month to identify all of the required replacement parts, find the best new stock options, and have the parts delivered. Both amps worked at power-up after the rebuild.

A list of rebuild parts can save significant down-time. (I can't help). ANYONE with an open amp and a camera can help construct this parts list.


I would never clone a KSA250. A custom 4.5KVA transformer alone would cost $1500. The circuits and components are "dated". The current philosophy is to use electronic Xovers and build one modest wattage amp for each speaker. On-Semi ThermalTrak output transistors minimize ClassA/B hash.

If you can find a clean KSA250 at a fair price, then I think it is worth the rebuild time and cost. Think of the KSA250 as an ancient art object for your home. By today's standards, the KSA250 uses overly complex and awkward circuits, inefficient heat management, Old School Engineering ... BUT it has a REALLY BIG power supply and MANY output transistors that smooth over its sins.
 
#11
#14
jacco vermeulen said:
You sound like a tourist.
(my attorneys have some of my cash, hence why I so badly would like my hands around one)
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@ jacco vermeulen: Ok, Thanks for that 🙂 I see you're as friendly as the rest of the people here in Netherlands. btw, I am Afrikaans, English is not my native language !

Zero Cool said:
I own a KSA-250 and plan on doing a full teardown and rebuild of it this winter. I am interested in this project and might be able to supply info and photos as i tear mine down. I am hoping I can derive a schematic!

It is my understanding there are 3 versions of this amp! so if you plan on buying one, you will have to first decide what generation of 250 to buy!
Click to expand...

@ Zero Cool: Now that's what I want to hear ! Awesome ! I plan on building the original version, but some nice photos and a few measurements is all that is necessary really 🙂 you should post some progress here when you get down to it !

LineSource said:
I rebuilt two KSA250s several years ago. They still are in daily operation behind Apogee Full Range Speakers. I spent about $600 in replacement parts for each amp. I have a large workbench with both compressed air and a powerful vacuum, as well as several different solder/de-solder stations. It took me 16 hours(1 weekend) to clean and rebuild each stereo amp(8hrs work, 8hrs confusion). It took me 1 month to identify all of the required replacement parts, find the best new stock options, and have the parts delivered. Both amps worked at power-up after the rebuild.

A list of rebuild parts can save significant down-time. (I can't help). ANYONE with an open amp and a camera can help construct this parts list.

I would never clone a KSA250. A custom 4.5KVA transformer alone would cost $1500. The circuits and components are "dated". The current philosophy is to use electronic Xovers and build one modest wattage amp for each speaker. On-Semi ThermalTrak output transistors minimize ClassA/B hash.

If you can find a clean KSA250 at a fair price, then I think it is worth the rebuild time and cost. Think of the KSA250 as an ancient art object for your home. By today's standards, the KSA250 uses overly complex and awkward circuits, inefficient heat management, Old School Engineering ... BUT it has a REALLY BIG power supply and MANY output transistors that smooth over its sins.
Click to expand...

@LineSource: I know the KSA 250 is in no way modern, but it's still a remarkable amplifier, and this is more about the challenge and fun of building my entire audio system from scratch than anything else .. I will most likely build a custom power supply for it and some water cooling for the inefficient heat-sinks. but we shall see.


Phisci said:
If I may make an alternative suggestion: Why not clone the KSA200. The schematics are available on the internet, it was deemed to be a great sounding amp, there are published mods, it's stable into the most demanding loads and some other guys have worked on its brother, the KMA160/KSA80.

http://www.diyaudio.com/forums/solid-state/42357-reverse-engineering-krell-kma-160-a-19.html

http://www.amplimos.it/images/Krell%20KSA100%20EUR%201989.pdf
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@Phisci: That's a cool idea 🙂 I was going to build KSA 100 and 50 for my other speakers, but I firstly want the KSA 250, and also no one has done it yet so its going to be "interesting" 🙂 but I will look more into the 160 and 200 ..

Luke said:
this is a big undertaking.

Krell KSA-250 recapping - YouTube
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@ Luke: yehp 🙂 but its all about the fun of it

superR said:
TS, look at our country's "marktplaats". There's one on for (asking price) 2700 dollar.
Marktplaats.nl > Krell KSA-250 2x 250rms klasse A - Audio, Tv en Foto - Versterkers en Receivers

Why not buy that one and refurbish it? If I look at the internals, this is not a project one would copy/clone due to the shear size of "everything".
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@superR: I was considering that one .. but I want to see what else turns up .. but will most likely end up taking it ..
 
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#15
mozartsghost said:
I see
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Your assumption that an amplifier can literally double it's output power in half the load is plain wrong.
Max output voltage will always be lower at a lower load impedance, there's a handful of reasons for that.
Exactly the reason why they came up with the "conservative power rating" jive.
A 500W in 4 ohm power amp will do something like 325W continuous power in 8 ohm.
So they'll tell the customer it does 250W/8 and 500W/4, instant "stable as a rock" amplifier.
Assuming a KSA250 will do 640W in 4 ohm because for real it can do 320W in 8 ohm implies that your understanding of amplifiers is at brochure and audio magazine level.
Not the smartest starting position for cloning the likes of a KSA250, '90s and later Krell amps are rather complicated animals.
You're welcome.
 
#16
jacco vermeulen said:
Your assumption that an amplifier can literally double it's output power in half the load is plain wrong.
Max output voltage will always be lower at a lower load impedance, there's a handful of reasons for that.
Exactly the reason why they came up with the "conservative power rating" jive.
A 500W in 4 ohm power amp will do something like 325W continuous power in 8 ohm.
So they'll tell the customer it does 250W/8 and 500W/4, instant "stable as a rock" amplifier.
Assuming a KSA250 will do 640W in 4 ohm because for real it can do 320W in 8 ohm implies that your understanding of amplifiers is at brochure and audio magazine level.
Not the smartest starting position for cloning the likes of a KSA250, '90s and later Krell amps are rather complicated animals.
You're welcome.
Click to expand...

Yehp, you're absolutely right. I have never designed an amplifier before, but I have designed other things, and this just seems like a very interesting challenge for me.

Thanks for insulting me again a second time 🙂
 
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