Explorations in 21-Century tango abound on this well-crafted, surprising disc by San Francisco’s Tango No. 9. The chamber ensemble was formed in 1998 by violinist Catharine Clune and also includes piano, accordion—not quite the same as Astor Piazolla’s bandoneon—and trombone. The quasi-classical quartet approaches the compositions with sincere gusto and highly accomplished musicianship. Most of the songs on Radio Valencia, their second CD, are the quartet’s own arrangements of time-honored tango compositions. A track such as “La Puñalada,” while relatively short (only 1:49), displays each musician’s instrumental proficiency, as well as the ensemble’s near-telepathic interplay. It’s rare for a U.S.-based ensemble to sound so cosmopolitan; one could swear they had honed their skills in Paris or Buenos Aires. At the same time, there’s a modern feel to their music. On this evidence, Tango No. 9 seems to be gearing up for a long and impressive career.