To my knowledge , the only 'strap on' that was actually a synth was the Moog Liberation.The rest are simply controllers - they make no sound of their own , just send out MIDI data . Yamaha produced two , one with 'mini'sized keys and one regular . I use three others: a Korg RK100 (1984), Roland Axis (1985), and a Roland AX-1 (the only strap on being currently marketed). There were a few others by minor companies . Oh , yeah , Casio made one also . Hope that helped.-Mikeferd Abbott