i'm asking this question and i probably already know the answer.

i have played on some 30 watt amp with a ic400 with emg 81
the sound wasn't really good, in fact i found that my other guitar sound really more nice.

and then i play in a marshall jcm 2000
and the emg 81 was far better than the other stock pick-up of the guitar

Is it normal, or i'm the only one who thought that???