The preamp on my Series II Carvin R600 is starting to crap out again. I had it fixed for the same reason a few months ago and it worked great until now. Now it's giving me a weak, distorted signal and extremely low volume. It's not my onboard bass preamp or the R600 power amp, both of those are fine. The problem happens with both the tube and solid state channels. What could be causing this? Anyone else had this problem?