Krell KSA 250 - The Mother Clone !!!

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#21
@Jozua:

I actually replied, but they deleted my post ..
This project did not quite take the path that I was hoping for .. I will eventually buy a KSA 250 and clone it still .. I do have the electronics skill to repair it myself. But just hoping I can find one for a good price right now .. not really worried about re-sale too much anymore since I don't think anyone else will join the project ..

*sigh*
 
#22
I like your enthusiasm, but as the owner of two of these amplifiers (a version 2 and 3) I think you may be trying to bite off more than you can chew. I am in the process of trying to fix a low frequency oscillation on my version 2 amp for which I just finished a complete recap on. Part of the work requires desoldering and soldering 56 output transistors. The bias and protection circuitry are complicated on this amp taking up half the space on the input board and a third of the output board. Some of the parts are hard/impossible to find such as the J102 input JFETs, 2N5564 matched JFETs and MC1747 dual opamps.
 
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#23
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...

Bingo .. !!!!!
 
#25
A version 1 is easy to identify since the speaker binding posts are oriented vertically instead of horizontally. The difference between a two and three is a little harder to discern. The soft start board is different and there is a series of 5 radial lead capacitors in line near the front of the input board on a three whereas a two has a single axial lead cap. (I suppose you could ask Krell based on the serial number but i asked them a question about my amp and they have yet to respond.) From a functional standpoint the later version runs at a slightly higher bias and the two channels have a staggered start instead of both coming on at the same time. After I get my version two repaired I intend to rebias the three to the same level as the two for less heat output and higher reliability.
 
#28
Got one KSA 250
Many failures in the front board replaced most of parts with problems but without schematics this is a real pain in the a**

At the moment amplifier clicks but actually after power up there is one capacitor that blows probably from reverse voltage even though nothing was messed up there or capacitor replaced in wrong polarity

it seems that voltage turns to reverse when you power down the amp or something like that

capacitor is on the piggy board C 13 100uf / 100V

Any help will be welcomed

thank you
 
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