The Oberheim OB-X was the first of Oberheim's OB-series polyphonic analog subtractive synthesizers. First commercially available in June 1979, the OB-X was introduced to compete with the Sequential Circuits Prophet-5, which had been successfully introduced the year before. About 800 units were produced before the OB-X was discontinued and replaced by the updated and streamlined OB-Xa in 1981. The OB line developed and evolved after that with the OB-8 before being replaced by the Matrix series.