VOPM VOPMfree vstFebruary 15, 2016FM, Mac OS, SYNTHS, Windows VOPM is an emulation of theĀ Yamaha YM2151 (OPM) 4 operator FM sound chip. Yamaha YM2151 (OPM) 4 operator FM sound chip emulation. Supports MIDI CCs. VOPM-win.zip VOPM-mac.gz