great idea, great tone, unfortunately very questionable execution, probably the worse GK product of all times.

1st amp was noisy out of the box with very poor signal to noise ratio and was only usable with treble turned down to <30%, 2nd one was better but boost is not usable, and after ~1hr at ~150wt volume starts breaking up and shutting down due to elevated level noise.

Funny thing that all problems centered around pre-amp/tone section, running directly into power amp via external pre-amp produces zero noise.

Don't buy it get RB700 if you are after GK tone.

“What ‘cha got there, some little pre-amp?” said a fellow bassist looking at the MB2-500 perched on my Trace Elliot 4X10. “No, my friend, that is the 500 watt Thunder Box!"

GK's MB2-500 is light, compact, simply laid out, and yet has the tone shaping circuitry to get a wide variety of sounds. Take the Contour and Boost knobs for a spin, and use the well thought out EQ to find the tone you like. Leave the DI box at home, as the unit has an XLR out that can be set for pre or post, and a ground lift switch. I love the tuner output, and although I’ll probably never use the effect send/return, it’s nice to know they’re there. The combination Speakon/1/4 inch outputs are innovative and save real estate on the back panel.

Oh, and this thing CRANKS. The first gig I played with it was an outdoor show, and it had plenty of power with headroom to spare. And did I mention it’s light? Less than 4 pounds – unbelievable.

I played on a show with another band and the other bass player had a big 1000 watt amp with 8-10 cab. I saw them looking at my little GK Micro Rig with 2-12 cabs. When I played my 12 string bass through it they were blown away!! I didnt have to go past 3 on the volume. WOW

I have a GK combo amp & cab that I love (except for the weight), so I was intrigued when I got to play through this at a show. The bands that night shared their backline. Everything went smoothly for me, but this amp shut itself off mid-song for 2 other bassists. The power light would turn orange and then nothing. It would come back on only to shut itself off again a few bars later. In fairness, these bassists are pretty loud and heavy, and the amp was working hard all night long. Shutting off unexpectedly is unacceptable though.

I could not believe how much sound comes out of this little amp! I've been playing for years and have owned lots of amps. Love that big GK tone! A++++