Frank Bang claims his heart is pure rock 'n' roll, but his soul screams the blues. Like Mike Bloomfield and Paul Butterfield before him, it is a combination of raw talent, hard work and devotion that has earned Bang a following among blues loyalists. Guitar legend Buddy Guy selected Bang to play alongside him on his world tours, and he has performed for Jay Leno and Conan O'Brien as well. "We are not a jam band, just a band that jams," he says. Frank Bang's Secret Stash performs at 10 p.m. today and Saturday at The Jazzhaus, 926 1/2 Mass.