Amp sounds fantastic. I seem to lose a little gain when the effect loop is active. Master sounds pretty good. I'm VERY happy with this amp. It's really a fabulous rock and blues machine.
I also love this amp, with the master volume you can dial your volume for bedroom playing (even with a 4x12) or stage volume when you need it. It gets VERY loud fully cranked and possibly too loud on stage too... This isn't like other amps like 18 watt where power amp distortion is needed for good tone, it's like a JCM800 where the sound comes from preamp and power amp distortion is typically f----ing loud, so the master volume works great. The in between is great for blues and cleans are good enough for church or jazz playing. The cranked tone can be used in modern metal however for that ultra high gain you'd need a pedal.