I just installed my Tonewood amp in a new Martin Special Dreadnought 11E that has a Fishman MXT pickup. I'm trying to adjust the master gain but it literally has no effect when I change it. The signal is just too hot and nothing changes,even at 5%. Any suggestions?
Make sure you start with the volume on the pickup set to 50% before setting Master Gain. I do see that the MXT is equipped with a phase button right above the tuner. Try pressing the button for a phase inversion. This may help as well. Other than that, it's worth checking on placement. Make sure the TWA isn't too close in proximity to the center of the guitar. The closer the TWA is to the pickup in the saddle, the more prone to feedback it'll be.
I'm generally able to set Master Gain at about 35-40% on Fishman undersaddle systems. Shoot us an email at email@example.com if you continue to have trouble.