Ordered a MB500 - LOVED the tone but it had a defective mute switch Sent back on my dime ($21.75) and added additional monies for a new MB800;LOVE the tone and power This one has two problems * You have to push the gain B knob in just the right place for it to switch channels (the back side of the knob opposite the indicator); the A gain works perfectly * The master volume is supposed to be a push switch to defeat the limiter; this pot does not move (either in or out) I doubt that I will ever use this feature but fear the pot may have problems in the future as the push function does not work It is clear the pots are a bit sloppy in that they will wiggle when turned gently. I assume they were chosen for size and price but expect a pro amp to be a bit more precision. The last thing is the QC that has not ben performed when the amps left the factory; the above happened right out of the factory sealed carton on both units. Anybody else have this issue? Is it worth trying one more time? Ironic that the tone is perfect yet the controls have not been right on the 2 I've had. If anybody from GK sees this post; HELP! PS - I bought an ancient 400RB (attached power cord) just to compare the tone to the 500; it sounded great and very close. Ironically this amp is quite old, a bit beat up. yet the controls all work fine.