San Francisco Chamber Orchestra concerts induce uneasiness in the hearts of the jaded and the cynical. After all, they feature world-class players, renowned guest musicians, and top venues, at no cost whatsoever. There's gotta be a catch, right? Will we be pitched for a timeshare? Are we being abducted by Moonies? Will we be pressed into selling magazine subscriptions? Actually, there is no catch — and even the obligatory invitation to become a member and help fund these free concerts is done quickly and painlessly. Then it's on to the shows, held within city limits at Herbst Theatre or the Contemporary Jewish Museum, which are really spectacular. In fact, a concert earlier this year featuring guest clarinetist Dimitri Ashkenazy shepherded us into the winter evening with that exhilarating "I love being in San Francisco right now" feeling, the virtuoso's encore rendition of an Artie Shaw clarinet concerto still ringing in our ears.