Krell KSA100 vs Threshold 400A vs McCormack DNA 0.5

Finally, this was the worst decision I made. I received the amp and I will perhaps never hear it. The protection circuit stays ON and the amp made smoke. Regulator mosfet toasted in the amp. I wtote to Steve McCormack and here is an answer I got:

The problem you are describing is an issue we now see frequently on the original DNA-1 and DNA-0.5 amplifiers that are now over 25 years old.

It is an issue that we no longer consider repairable. The problem is with the through-hole plating between the top and bottom of these two sided driver boards.

Repairing failed components and mending the connective traces can sometimes revive the amp for a short time but doing this is not recommended. The underlying problem is still there and it will continue to get worse.

This problem only pertains to the main driver board, not the two output
boards.
Seller offered me to return the amp or send me back $200 so I could repair it. I have no problems to do repairs but as SM advised me, it seems risky to repair it. 

I hope this could help DNA1 and DNA0.5 future buyers. I know there's upgrade for these amps but they cost an arm ($900)

@legarem 

What does the seller have to say about the condition of the amplifier he sold you?  IMHO he should finance the new driver board you made or let you return it to him for a refund.

 Steve is being absolutely truthful.  Same thing he told me about my 21 year old DNA-1.  They are seeing a consistent pattern in the degradation of the driver board over time.  It is just not the unrepairable nature of the amp but rather that in the years that have passed, Steve has been refining his modifications to the DNA amps.  My previously modded DNA-1 was $1300 for a new driver board, wiring, input and output jacks and new improved soft recovery diodes.

The amplifier is now reference class!  It really is fabulous.  I almost feel guilty getting that much bang for the buck.

If you don't have the money now I can see how that is a problem in your case.,  But... you can't expect SMc Audio to repair something that is going to fail soon again.  

Another vote for Sumo products. I had a son of ampzilla and it was sweet but I don't think it was 100W??
there was a nice sumo nine up on one of the sites....
or go with the krell

Get $ back
then get a DNA thru Steve

Finally as the amp is super clean, I decided to keep the amp and seller lowered the price a lot ($307). I must say first that the amp had a problem when I bought it. I payed it accordingly because he also thought it was only a bad cap to replace. There was a bulged cap inside near a mosfet regulator which I replaced. The amp worked for one day on the bench then failed when I connected the speakers on it. The seller gave me the choice to take it back. but I had to pay for shipping back. As i’m good and equipped for electronic repairs I really want to diagnose this beast. I will surely try to repair it and if I can’t, as Steeve wrote to me, I can at least get the money I payed for it. I know this is risky but.... The only thing I would have liked to get from Steve is the damn schematic for this amp. I got the power supply schem but not for the driver board. I already diagnosed a bad mosfet in a regulator feeding the front end and the drivers.The bad cap probably weakened the mosfet I hope everything is good after the reg.