Just got me an MB212 yesterday. Alan, G-K should send you at least a few t-shirts, or extended warranty for your amps, because I think you are responsible for quite a few sales of these amps. . . LOL.
Well, my initial impression is not exactly "wow." I put it side to side with my current rig: Schroeder 1212L and Markbass LMII. I like the sound if this rig, but I wanted something with a little more low, low end, and the Schroeder can sound a bit boxy sometimes. And also I wanted to add another cab/amp for larger stages where the 1212L has not been enough, and I wanted something even lighter (the 1212L is 42 lb, and the LMII is 5 lb, so I'm saving 10 lb total with the MB212).
The MB212 sounds great, but in comparison to the 1212L/LMII, it sounds like if I had put a blanket over the amp. There is a lot more definition to the note in my rig, a lot more punch, and the highs are tuned lower in frequency that in the MB212, which is nicer. The sound overall is a lot more aggressive than the MB212. The 1212L also has a lot more low down below - but as Alan has mentioned a few times, these speakers need to be broken in and they will deliver more lows over time. I'm counting on that.
The 1212L/LMII seemed to have a bit more volume, but the MB212 seemed to spread the sound around it a lot more, filling more the room. The1212L is quite directional.
I'm hoping that the lack of a ground lift in the XLR out won't be a problem. My bass goes through the mains in 100% of my gigs, and once in a while I've had to flip the ground switch. I guess I'll have to invest in a $29 direct box, although most clubs and sound companies have plenty on hand.
Another observation, I can't seem to hear anything different when I use the boost, just more volume. I thought the sound was going to warm up, but really couldn't tell the difference, maybe a bit more high mids? (I adjusted the gain accordingly when not using the boost in order to compare the sound at the same levels.)
The tweeter is just a bit hissy, and rather small. I hope it doesn't fry at high volume. Some mentioned that the tweeter is useless; well, I think it makes a big difference with brighter, active basses, but of course, passive basses sound just find with the tweeter off. I play with earplugs, so I tend to EQ a bit heavy on the high so I the sound is not muddy (in my head...)
And I think they went overboard with the contour switch. I think a gentler EQ curve would have been more usable, but it scoops the sound way too much.
Construction is indeed very nice at this price point. Only time will tell how will these hold up with use.
Tonight I have an outdoors gig. I'll report tomorrow. Great workingman's amp for the price, no doubt.