I was told that the Foundation S originally stood for Foundation with Schallers(both the pickups(PJ) and the tuners were originally Schallers) . However, Peavey made frequent changes to the line in an effort to expand their place in the market. Originally the Dyna-Bass was the active version, but I have seen several different Peavey models where a boost only pre-amp(passive tone maintained) was installed. I even have a Unity model(neck-through PJ) that is passive but has a route in the control cavity for a battery. It is very possible if not likely that Peavey made a Foundation S that was active. In general, most Foundations were passive, but I would have no trouble believing that you had an active version from the factory.
Peaveys can get a bit confusing if you try to follow their development. The more I have explored them the less likely I am to make blanket statements; with one exception, they are all extremely well made basses that are incredible bargains.