 Alternative versions of the Mellotron were manufactured by competitors in the early to mid @-@ 1970s . The Mattel <unk> was a toy keyboard designed to be used in the home , which played back sounds using optical discs . This was followed by the <unk> <unk> in 1975 , which used a more professional @-@ sounding version of the same technology . Its most notable user was Patrick Moraz . 
