How good is Krell Phantom III?

Uh, it is a Krell. If that is what you want, okay. To each their own.

10 Audio reviewed one of their preamps. Jerry was brutally honest.

Hard to say ... there is a Fangroup ...
I remember years ago I was in a Distributor room and the System was on Standby. A young tall man came inside, sporty clothes, dynamic, long haired with his girlfriend, her best days were gone, but you saw, in former years she was pretty... and said to her

Ahhh..... THAT‘S KRELL WITH Wilson 

went to the System, showed the Distributor a Thumbs up, returned and left the room ....

Krell with Wilson. In Seattle you had to go to Bellingham to find Krell with Wilson. In Seattle it was Mark Levinson with Wilson. 

Same (unlistenable) difference.

The Krell Phantom 3 was what the older Krell 280p evolved into.  It carries similar audio stages to the more expensive Phamton 2 and Phantom preamps, but the power supply is undersized (as was the 280p).  It is likely going to be a very revealing and bright preamp (others just do not like the Krell sound and describe it as harsh/unlistenable).  This is mostly due to the undersized power supply.  Their S1200 processor has the same problem.  Those Class A discrete analog circuits are very demanding on the power supply.  The fix is to increase the amount of capacitance in the main power supply.  The Phantom 2 has a much larger power supply.  The Phantom (1) has a separate power supply chassis (best out of the three).

@auxinput Thanks for that detail description. I am glad that I read your review before buying this preamp. In my opinion, it was not worth the price it is asking for. I am going for a MC220 preamp (paid $2300). I hope that it will be a much better choice for my MC352 power amp.