The Roland GR-77B is a bass synthesizer. It was designed to be used with a G-77 bass guitar. Brownmark used a GR-77B with Prince, but had his own pickup built into an Alembic Spoiler, so he could avoid using the G-77 bass.
A Fender Jazz through an Ampeg SVT, but the amp didn’t growl enough so I went to two Crowns and custom boxes with four 10s and an 18. I used separate preamps, a Lexicon phaser and parametric EQ. Here’s a secret about Prince’s sound: he liked everything mixed high, so the low presence would cut through. Eventually I migrated to an Alembic Spoiler and by the Parade album (1986), I had a Roland interface built in so I didn’t have to play that weird-looking Roland bass thing.