Krell KSA 100mkII Clone

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#2,721
Here is the KSA-50 MK-2 aka Delta Audio version that most of us built during the Ver. 1 boards. Note that a few things have been added that most people did not bother with like current limiting and resistors in series with transistor bases, etc because they were not in the original.
 

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#2,722
Mark Allen said:
KSA-100 MK-2 has constant current sources and KSA-50 MK-2 does not. Neither Krell used FETS for the input stage although later Krell's such as the KSA-80B did.

See schematic attached of KSA-100 Mk-2...

Mark
Click to expand...

I was talking about the 2nd stage FET diff pairs VN02 and VP02, that is the schematic that
I saw but it was done with CAD. Thanks for posting.

So was a KSA-50 ever made like that with just fewer output transistors?
 
#2,727
Kaplaars said:
Nice to see that there are still Krells being made! Fantastic amp farl, really love your design! But beware, putting that Krell logo in front of your amp could be dangerous... it resulted into a lot of negative feedback back in the day when I did something similar ;-). Actually mine is in full working order too, lgreen. Still using the Jims Audio boards which, I believe, are most close to the original design. However, after several accusations and renaming the original threat by someone, I have stopped with posting updates. I have made quite some improvements, especially with more efficient use of the heatsinks. It now does not exceed 50 degrees C. Indeed it is one of the best amps around. I am still enjoying it, although not on a daily basis; it consumes A LOT of power haha.

An externally hosted image should be here but it was not working when we last tested it.
Click to expand...



Kaplaars,

Can I know what front button you are using?

Thanks,

Davide
 
#2,729
Has anyone ever found out what is on the secondary board in a KMA-100? In this attached picture you an see the driver board as well as what appears to be a secondary power supply regulator board and a third board with capacitors and probably rectifiers. Does any schematic exist for the KMA-100? I am about to build a pair of mono blocks from completed boards I've had laying around since this thread began.

Thanks!

Mark
 

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#2,730
Mark Allen said:
Has anyone ever found out what is on the secondary board in a KMA-100? In this attached picture you an see the driver board as well as what appears to be a secondary power supply regulator board and a third board with capacitors and probably rectifiers. Does any schematic exist for the KMA-100? I am about to build a pair of mono blocks from completed boards I've had laying around since this thread began.

Thanks!

Mark
Click to expand...

Yes,
It`s a front end regulator.
Big improvement to the sound...
Your picture is of KMA-100 MKI
 
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#2,739
Ok Andrew, thank you for your answer, I'll try to be more specific:

General: It’s been a while (almos 20 years) since I build an amp with TO3 devices so I wonder if there’s some new material that i could use for isolators besides mica. So for my ongoing KS100 clone with 4 pairs of TO3 devices, I'm looking for the more thermally conductive material I could pay.

You say:
Does the Rth c-s meet your requirement?
Barely i think, but this is my first time building a "heater" amplifier like this with T03 devices and I'd like to get the best thermally conductive material.

Does it insulate for the voltages you intend to use?
It was my understanding that almost any isolation (mica or pad ) was good for less than 50 volts?

Does it have a one use limit? Is that OK?
Yes, it's fine to discard them in case of transistor replacement if that makes it more thermally conductive. The original Krell is a very hot amp so anything we can do to control heat is welcome.

Any suggestions? Last time i built a To3 device was with mica and thermal compound a long time ago.

thanks
 
#2,740
What is the maximum voltage the driver boards can be ran at? I have a Krell KMA200 PSU including regulator, but it runs -+80v for the driver board and -+70v for the output devices.

What changes would need to be made to adapt this to those voltages?
 
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