I just bought a marshall dsl40c combo. Under classic gain channel, I set the same volume, gain and EQ, however its crunch sound is much louder than the clean sound. Is such situation normal?
Yes. Crunch works by adding more signal from the first preamp stage to the next stage so it always boosts volume too. It can't help it because the two settings share a volume control. It's usually at its worst when the clean gain is set low, so try keeping the gain up a bit and clean up with your guitar volume instead.