The aux input is designed to take a line input signal such as an mp3 player, as you guessed, a tape deck, cd player, keyboard etc whereas the normal input is for low level signals such as bass and guitar or any instrument that needs a preamp. It will work OK however, I'm not familiar with the Tech 21 Blonde pedal but you may find that it does not have enough output but then again it may. Try it and see, you won't damage your amp.