The Oberheim OB-SX is a polyphonic analogue synthesiser. It is similar to other keyboards in the OB series, but had a selection of presets rather than having a full interface. Prince liked working with these presets. He used one in the studio on the Controversy and 1999 albums. He also had his own OB-SX on stage on the Controversy tour.
It was also used live by Lisa Coleman. Dez Dickerson played one in the Let’s Pretend We’re Married video.
Prince was incredibly bold in the way he would just use a preset and then brighten the fuck out of it! He would turn the filter way up so the sound would cut through the mix. I still have the OB-SX from those days. It’s one of the most simple Oberheims - there are just a few knobs on it, but that was the most quintessential keyboard from that era.