The Oberheim OB-Xa is a polyphonic analogue synthesizer used by Prince, Lisa Coleman, Dr Fink and Boni Boyer. It is part of the Oberheim OB range that included the OB-X, OB-SX and the OB-8, all used by Prince. It appears in photographs and videos from the mid 1980s, and Dr Fink has discussed its use in interviews.
The OB-Xa was Prince's primary keyboard on the 1999 album. The introduction to 1999 is played on an OB-Xa layered with an Arp Omni-2. Dr Fink and Lisa used OB-Xas on the 1999 tour and the recording of Purple Rain. Despite Prince moving to the OB-8 in the studio, Dr Fink and Lisa continued using the OB-Xa live and they were used the Purple Rain and Parade tours. The OB-Xa has a reputation for having a rawer sound than the OB-8, which might have made it preferable for live use. The OB-Xa was also used live by Boni Boyer on the Sign O The Times tour.
He would just put three or four tracks of Oberheim sounds together and use different voicings to make it thick and fat. The Oberheim was the main synthesizer he used in the studio back then. He used the Yamaha CP-80 electric grand too, but for synths, the Oberheim was the main axe. In the earlier years, he always liked to have a real strong lead line tone incorporated into his songs; that was a trademark of his. If you listen to "Delirious," from 1999, there's a real high Oberheim patch with a lot of modulation in there. It’s real lively – kind of a cross between an organ and a square wave.
He had a drum set and every keyboard of the day - the Oberheim and the Omni, which [the Omni] was a very integral keyboard used on 1999. He didn't use it much on 'Purple Rain', but was really using the Oberheims quite a bit on the Purple Rain album.