Fiddler Vassar Clements grew up in Kissimmee, Florida, listening to big-band jazz at local dance halls and to the Grand Ole Opry on the radio. In the mid-40s he was captivated by Chubby Wise, whose mercurial violin provided much of the harmonic complexity and emotional intensity in Bill Monroe's fabled "high lonesome" bluegrass sound, and in 1949, at age 14, Clements sat in with Monroe's band, the Blue Grass Boys. Within a few years he'd replaced his idol, and he went on to accompany country stalwarts such as Mother Maybelle Carter and Hank Williams, as well as more forward-looking artists like Waylon Jennings. But it wasn't until the 70s that Clements made the records that would win him his largest and most enduring audience: he appeared on the Nitty Gritty Dirt Band's triple LP Will the Circle Be Unbroken in 1972, on the Grateful Dead's Wake of the Flood in '73, and on the debut album from Jerry Garcia's Old & in the Way bluegrass project in '75. This crossover success with the hippie folk-rock crowd opened doors for Clements, and in the years since, in addition to working with modern bluegrass stars like Ricky Skaggs, he's ranged far from his usual territory, playing with jazz bassist Dave Holland and swing violinist Stephane Grappelli, among many others. On his current disc, Full Circle (OMS), Clements saws, scurries, and leaps through everything from Cream's "White Room" to mountain chestnuts like Flatt & Scruggs's "Your Love Is Like a Flower." On his long lines, he uses adventurous intervals and crisp, balanced double-stops to probe unexpected melodic and harmonic directions, but even on his most unlikely covers he never wavers from the bedrock tropes of bluegrass. He exploits the complex major-minor key tensions in the Cream tune to create both anxiety and a sense of weary resignation; on "Out in the Middle of Nowhere" he livens up the pedestrian melody by digging deep into his trick bag, coming up with all manner of shrieks, whoops, dips, and caterwauls. And he rips through the Beatles' "I've Just Seen a Face" as though it'd never been anything but a bluegrass tune, soaring ecstatically over the opening lines, then digging into the body of the song with the classic high-lonesome blend of mournfulness and joy. Saturday, March 16, 7 and 10 PM, Old Town School of Folk Music, 4544 N. Lincoln; 773-728-6000.