I've got a Rumble 75. I am debating whether to keep it or not. Can't quite get the same high end bite out of it as I can with my Ampeg BA108. Got a BA112 on the way to compare.
I have to turn the treble and midrange tone controls up to 9 to get the same top end out of this that I can get out of the 108 with the treble tone set to 7 and everything else set to 5 (12 o'clock). This is with a Fender American Deluxe Jazz Bass which has a good amount of top end naturally.
The bottom end is nice and full though. MIne had an annoying buzz behind the faceplate where the Rumble logo is, which I thought was kind of funny. I loosened the mounting screws and shoved a thin strip of rubber between the amp chassis and the cabinet and that seemed to quiet it down, at least for now.
I have two places at my house where I play on opposite ends of the house, so I might keep this and put it back in the jam room with my Hammond C3 and minimoog. Beats having to lug an amp back there everytime I want to just jam along with some drum patterns, or host a guest bass player to let me play some keyboards.
I have to admit that despite the huge difference in tone control settings between this and an Ampeg, it is growing on me the more I play through it.