The DuSable Museum of African American History gets its own version of the Grant Park Symphony this weekend when "Jammin' in the Park" returns to Washington Park. Playing for the picnickers will be veteran pianist John Young, who is surely the romantic to end all romantics. He loves intricacy, so he tends to underline complex bop melodies with low bass rumbles, then suddenly turn the solo into the dirtiest of blues; or he'll play grand, lush, swooning chords to climax a ballad, then subvert them with dying-butterfly triplets. He improvises like an arranger, and behind his broad, infectious smile is a serious and subtle spirit. His high romanticism and considerable range and erudition virtually define Chicago's distinctive brand of modern jazz piano. Joining him will be Paul Serrano (trumpet), Dan Shapera (bass), and George Hughes (drums), along with sitters-in. The concert, cosponsored by the Jazz Institute of Chicago, is part of the museum's Arts and Crafts Promenade and Family Festival. Sunday, 6-9 PM, DuSable Museum of African American History, 740 E. 56th Pl.; 947-0600 or 427-1676.