Resonance in Peavey amps is a high-pass negative feedback loop. Turning the control up reduces the amount of feedback voltage at low frequencies and makes for a looser low end. It's a feature they borrowed from their guitar amps that's mostly useless for bass players.
RE the VB-2 (which has almost nothing in common with the Alphabass, which is a Fender Studio Bass copy with a Mesa-style s/s graphic EQ) The VB-2 uses EL34's and depending on output tube quality and biasing, could be a VERY different responding amp if not set up right. I played one and was super impressed with it and it exhibited none of the constipated qualities is showed others. It sounds nothing like a Mesa, but that Alphabass and early Mesa Bass 400's are both brothers off the Fender family tree and from what I've seen of the new Mesa Prodigy, it still follows that line. The VB-2 is a completely different animal: active s/s preamp that doesn't sound like it and a very hi-fi like output section. I'd buy one in a SECOND if I had the money.
