Abstract: A plug-in adaptor for playing standard cassettes in an 8-track stereo cartridge player, wherein the mechanical power for playing and rewinding the tape in the cassette is provided by the capstan of the 8-track player. A pickup head in the adaptor senses the magnetic signals from the cassette tape as it is driven past the pickup head, and these signals are amplified by an adaptor amplifier and supplied to a magnetic coupler in the adaptor adjacent the 8-track tape playback head, which receives the signals for transmission to the electronics and speakers of the 8-track unit. Electric power for the adaptor amplifier is drawn from an 8-track tape sensor ordinarily used to sense the end of an 8-track tape.