Salsa ensembles are typically based on one of two different Cuban instrument formats, either the horn-based son conjunto or the string-based charanga. Some bands are expanded to the size of a mambo big band, but they can be thought of as an enlarged conjunto. The traditional conjunto format consists of congas, bongos, bass, piano, tres, a horn section, and the smaller hand-held percussion instruments: claves, guíro, or maracas, played by the singers. The Cuban horn section traditionally consists of trumpets, but trombones are frequently used in salsa. The section can also use a combination of different horns. Most salsa bands are based on the conjunto model, but the tres is almost never used