I think I already know the answer to this question but thought I would throw it out here anyway. I am a seasoned guitar player and I am using the HD500. I recently began learning to play the mandolin and seem to be progressing a lot faster than I thought that I would. So I began thinking about running my mando through the HD500 as well. I haven't locked in on which pickup I will be using but leaning towards a K&K Twin internal pickup which consists of 2 transducers to a single endpin jack and it has no built in preamp. So my question is will I still need a preamp before running it into the HD500? I am assuming that I will but thought I would see if anyone else has already done this with a mando, acoustic guitar, etc.