Yamaha TX81z For Sale. MIDI Sound Module. This cute little 4 operator FM synthesizer rack is 8 part multitimbral. This is a great cost effective intro to FM synthesis. Perfect for sharp, cutting sounds most other synths can't touch. Similar to the classic DX7. This rack contains the same synth engine that's inside the DX100, DX21, DX27 and DX11. Email for pics.