Alright, I have much more experience with guitars tahn bass, but I know what i am looking for soundwise...

Right now I am running a Fender Rumble 100 with an Ibanez GSR 200 bass.  I have a Rocktron Austin Gold stompbox to give a little more growl and volume when I need it, but it doesn't really give the rolling, thick, crunchy, growling sound that I want.

So....I need some suggestions to get the sound i am looking for.  To give you an idea, I would like to be able to make the same bass tone and sound as the heavy duty bridge in "sabbath, bloody sabbath."   If the effet pedal has a line control to allow clcean signal through that is a huge bonus.  My budget is pretty much limited to $150 or less at this time.

FYI, switching amps and/or bass is not really an option at the moment for various reasons.  Also I really like the bass and amp and they work very well for the other 75% that I play clean.  Just need something to fill out for the 25% of heavy stuff.

Thanks!