Yamaha's first synthesizer was the SY-1 in 1973 Then came the SY-2 , and the HUGE GX-1 . In no particular order was the CS-01 , CS-5 , CS-10 , CS-15 , CS-15D , CS-20M , CS-30 , CS-40M , CS-50 , CS-60 , CS-70M , CS-80 , EM-80a mixer with preset drum machine , SK-10 , SK-15 , SK-20 , SK-30 , SK-50D , SS-30 string machine . Their last analog synthesizers before the DX-7 was the SK line , the CS-70M , and the small CS-01 . Yamaha synthesizers were not selling well at all , and the problem went back to the late 70s . The DX-7 saved their asses and put money in their pockets .