Two years ago four seasoned string players, all graduates of the Moscow Conservatory during its heyday in the 70s, formed the Kopelman Quartet. First violinist Mikhail Kopelman was a founding member of the Borodin String Quartet and played with it for 20 years, then played with the Tokyo for seven. Second violinist Boris Kuschnir, a student of David Oistrakh, was a founding member of the Moscow String Quartet and a teacher of Nikolaj Znaider. Violist Igor Sulyga, also a founding member of the Moscow quartet, worked with Shostakovich on his late quartets. And Mikhail Milman, a student of Rostropovich, was principal cellist with the Moscow Virtuosi for 20 years and has performed chamber music with Evgeny Kissin and Yuri Bashmet. Despite their impressive backgrounds, as a quartet they're not perfect. During their Ravinia debut this summer they occasionally had intonation problems, and Milman had a distracting habit of sniffing at the beginning of many phrases. But Kopelman is a remarkably expressive musician, and Milman's phrasing is superb, his tone gorgeous. All of them dig deep into a composition, taking risks and playing with uncommon passion and conviction. They also tend to program rarely heard Russian works from the late-Romantic and early-20th-century repertory. This program includes Tchaikovsky's Quartet no. 3, a work they played at Ravinia--a deeply moving performance despite the flaws. They'll also perform Prokofiev's exuberant Quartet no. 2 and Miaskovsky's Quartet no. 13, the last one he wrote. Friday 29, 8 PM, Mandel Hall, University of Chicago, 1131 E. 57th, 773-702-8068, $30, $11 for students.