You should call Krell and they will tell which jumper it is for you amp. It's very easy to change. You just need to open the cover and install a small jumper across a connector. Stereophile's review of the Krell 250M mentioned the procedure and connector location.
Tube pre-amps and Krell amps
Question for Krell owners. From time to time I read various threads regarding the use of tube pre-amps with Krell amps. The owner’s manual states that the coupling capacitors be engaged before using a tube pre-amp. The only instructions in the manual are to contact your local dealer. I don’t have a local dealer. Does anyone out there know how to do it? Can I do it myself? I would hate to lug it to a repair shop, it’s too damn heavy!