i have a crate gx-15r. and i was wondering if all the other gx-15r's did this....
i use a BOSS DS-1 distortion pedal and when i turn the volume on my amp volume up beyond 4 the distortion fades drastically and almost sounds like im just playing the clean channel.

i know i need a new amp lol. but tis all im workin w/ right now

p.s. i have a peavey v-type and jackson soloist
It's not a bad bad amp, but it's not great. The reason it does that is because the gain and OD break up past a certain volume due to the low wattage.