Recently, I picked up a Vox AC50 MKII head. I have connected it to a Vox Foundation cabinet (18inch speaker). Unfortunately, I can't seem to get a decent tone out of it. The normal channel sounds muddy, and I can't get a good clean tone out of it. When I put the volume at around 11 o'clock or higher, the tone is overdriven / distorted. I suppose this is not supposed to happen. Also the brilliant channel has the same problem (except for the muddiness). I tried it with several bass guitars (EB-3, Precision bass, Jazz Bass, Framus 50/150) Does anyone know what the problem could be? If it's helpful, I can make some pictures of the electronics. I am thinking about bringing it to a tech, but perhaps it's just a simple thing.