I thought I would start this thread just in case anyone is interested. I decided to buy a backup amp for my GK MB800. I'm a fan of Carvin gear and own a couple SB basses and a BRX10.2 Neo cab of theirs, so I thought the BX500 would make a good head to try as a backup. And it was on sale for $379 new, so I figured it was a good time to jump on it. (As I was typing this I just noticed they have them for $359 new on Ebay, grrrr) So I got the BX500 in today. Here's the pic: I had forgotten how much bigger the BX500 was than the MB800 immediately on pulling it out of the box. I also forgot how tonally flexible the amp is. I first plugged into the MB800 on my standard setting with everything mostly noon'ed up to get an idea of what I normally use then switched to the BX500. Immediately I realized that flat on the MB800 is anything but. I started with everything flat on the BX500, but the sound was no where close. I had to really dial in the Contour (scooping) knob on the BX500 from "Flat" to much closer to "Scoop" to get a tone similar to the "noon tone" of the MB800. Even then it was a little off. I looked around back on the BX500 and noticed the 12AX7 tube was engaged and went ahead and disengaged it since the MB800 doesn't have a tube. At that point, the BX500 tone was getting closer to the MB800, but still not quite there. I dialed the Drive knob on the BX down to zero. That got it closer. Still a little thick. I switched from active to passive and that made it a bit closer. Going back to the MB800, I found it was getting pretty close now. The only differences I could tell were in the high end and an overall compression feel that the MB800 had compared to the BX500. So I switched back to the BX500 and turned the treble knob up a bit trying to find that high end, but that wasn't the frequency I was hearing. I put it back to noon and engaged the graphic EQ on the BX. I made sure all of the other sliders were at noon and then went to the 5k slider and started edging it up a bit. I didn't think it would cover the right frequency either, but it was closer than the treble knob. I played and bumped it up a little more and that got really close to the MB800. At that point, I went back to the MB800 and A/B'ed them again and it was pretty close tonally at this point. The MB800 just has some sort of inherent "sweet" sounding compression on it. I went back to the BX500 and tried to dial in a little compressor using the onboard, but that didn't really do the trick. At this point there is a little bit of compression I can't quite match between the amps, but I'm still working on it. That said, I was surprised as how well the BX500 held its ground in the volume department and how close I could dial it in to sound like the MB800 in just a few minutes of fiddling around. From here I'm going to try it out with my fretless bass next and then take it on a gig this week and try to A/B them between sets to see how it works at a stage volume and in the mix. I can record clips directly to the computer, but the DI out on the BX500 is pre only, so really you would just be hearing my bass on that time of recording. I don't have anything high quality that I could use to do an in room recording. I guess I could mic it up if anyone is interested, but not sure I would really capture the differences or not. Let me know if you have any questions on the comparison of these two that I can answer.