yes, anyone reading this who is looking for a second hand pre, the KRC-HR is well worth looking into. its not fancy, it does not throw a huge 3d soundstage but its well sorted in every other respect. there are a lot of crapy pre amps out there, regardless of cost. i loved my KRC-HR, loads better than the standard KRC that i also owned and a great step up from the rather poor imo KAV pre amps. its the step off point for krell before they got obsessed by the CAST system that just seemed to add cost but no musical benefits imo.
i used mine with a few amps but it paired well with the KRELL KAV 250a amp, though i later upgraded that for a FPB200c but to be honest i am not too sure it was worth it. the KAV amps were good but the KAV preamp and KAV CDP were not for me. the real krell CDP 20il and the 25sc are beyond great, but when they go wrong your a bit screwed.. as i found out. i had my 20il plugged into a KAV amp, great combo. much better than most of my kit that preceded it that happened to cost a lot lot more.
bit off topic there, sorry about that.
if you can't get your Krell right the Belles pre amp i use seems to follow the same spirit but its a bit better imo.Belles LA 01. they are great value new or used. similar presentation, just more speed, balls and transparency. it drives amps hard so better make sure what your using can take it.
deoxit the volume pot on your krell, that helps a lot.
again i am sorry for your woes, we have all been there... i feel your pain
you should be able to find the circuit diagrams online.. schematics.