Actually, Ray Manzarek played the bass parts on a Rhodes keyboard bass. I have a few old Doors LPs, so I pulled them to see how the bass was credited. On the first Doors album, Manzarek is credited with organ, piano and bass. He is also credited with organ and bass on "Absolutely Live", but is credited only with keyboard on "Soft Parade". Harvey Brooks and Doug Lubahn are credited with bass on "Soft Parade".