Hey, I have a Blue Angel that I'm having some issues with, I've tried a few external preamps into the FX return, and something really weird happens. The sound with the external preamp is extremely muffled, very badly dark, and the controls on the preamp don't seem to do what they're supposed to; then very weird abrupt jumps in volume and brightness can occur, it almost sounds like feedback, sometimes it doesn't stop once it's started until I put it into standby. I know the preamps I've tried work well into the FX returns of other amps, so it's not their fault. I know the Blue Angel's loop is parallel, could that be causing the issue? When I'm going straight in the Blue Angel's front inputs all is well. Everything is fine with a cable straight from the send into the return also. I contacted Mesa and they recommended to see a tech, is there anything I can try myself? Maybe converting the FX loop from parallel to serial?