Appreciable enhancement of the acoustoelectric gain by longitudinal magnetic fields is observed in the classical regime (ℏ&ohgr;c<kT). The enhancement increases monotonically with magnetic field, reaching saturation at fields corresponding to &ohgr;c&tgr; being equal to a few units. The dependence of the magnetoacoustic enhancement on carrier concentration is analogous to that of the longitudinal magnetoresistance, both are more pronounced the lower the carrier concentration. The observed effect of the longitudinal magnetic field on the acoustic gain is similar to that reported for the acoustic attenuation in the quantum limit (ℏ&ohgr;c≫kT), but for the regime studied (ℏ&ohgr;c<kT) no theory has as yet been developed.