Here is the best way to adjust the internal trim on the Dirty Bomb;
Turn the internal trim down to a bit less deep bass than you think you could use (maybe even off), then dial in the character that you need by using the bass and treble controls on top the unit, I am trying to encourage players to be aggressive with the bass control (on top) when trying to get fatter or thicker sounds (lots of fundamentals). After you get your basic sound dialed in, and are sure you have the guitar "sitting right" with your band (or at home), bring the internal "sub bass" up until you have the deep bottom that matches your speaker cab and music style best. Keep in mind, devastating sub bass, with lots of top added in can have trouble competing with cymbals, kick and bass guitar. The closer your guitar sound
is to "native guitar frequencies", the easier it will be to "cut through" the mix.
If you are playing at home, feel free to make that sub bass "SLAM!", there is no worries about cutting through when you are solo, and all that bass is fun!