The Oberheim OB-X is a polyphonic analogue synthesiser. It was used by Prince on Dirty Mind and Controversy. The main riff to When You Were Mine was played on an OB-X. The OB-X probably appeared on 1999 and Purple Rain too, and it was in use as late as 1984 on "Manic Monday". It was also used live by Dr Fink and Lisa Coleman.
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.
That was definitely the Farfisa new wave sound that was happening at the time. We were pretty much using Oberheim OB-Xs to do that.