Sometimes the factors that condemn a musician to obscurity are beyond understanding. Jimmy Burns has been on the Chicago music scene for over 30 years, starting with close-harmony doo-wop groups in the 50s, and developing a repertoire ranging from the Delta blues of Arthur "Big Boy" Crudup to the mellow, gospel-tinged classics of Sam Cooke. Although his tendency to approach everything on the same even, measured emotional keel lends a "human jukebox" feel to some of his performances, his sure-fingered technical proficiency, his warm and deeply expressive voice, and his elegant sense of onstage professionalism should have earned him much wider recognition than he's received. Each time he performs amounts to a comeback by a talented local musician who's never really been away. Today, 5-8 PM, Cotton Chicago, 3204 N. Wilton; 528-1651. Tonight, 9 PM, Wrigley Side, 3527 N. Clark; 525-5909. Next Friday, May 26, Tip On Inn, 12132 S. Western, Blue Island; 385-9740.