Tubed preamp with Krell KSA 150 amp?

All I've used with my Krell KSA100s, FPB300 and FPB600 are tube preamps and never had any problems. The only issue I encountered is some tube preamp output impedance is too high and as a result, sound is dull and lacking LF/HF.

If you like MW, Dan is having a LS 100 preamp tour so you can audition before purchase. I think it's 6sn7 base so lots of tube rolling options. You can get more info on AC. Also there are several MW 36.5 on Agon that are reasonably priced.

I have not experienced any problems with tubes and Krells. They seem to work great together.

"Knghifi
All I've used with my Krell KSA100s, FPB300 and FPB600 are tube preamps and never had any problems. The only issue I encountered is some tube preamp output impedance is too high and as a result, sound is dull and lacking LF/HF."

what # would that be? I am looking at a modwright now (swl 9.ose signature) and I believe that the output is at 600 ohms...
thanks,
paul