In the first of Christoph von Dohnányi’s subscription programmes during the Boston Symphony Orchestra’s 2004-5 season, the young German cellist Alban Gerhardt was the soloist in the glorious but still-neglected Cello Concerto of Robert Schumann. On the first night the A string of his cello snapped mid-performance, and principal cellist Jules Eskin handed Gerhardt his own cello to continue. ‘It takes a long time to change a cello string, and I didn't want to keep you waiting,’ remarked Gerhardt before offering an encore of solo Bach.