The problem is that when I put the distortion pre fx my amplifier does not give the sound even with any preset, the other effects work correctly only the distortion does not, however when I connect my headphones I get the distortion sound but without the headphones it sounds

Today I tried to connect my guitar via iRig and a common audio cable to my Code 50.

The sound was really muddy without any treble... Same when I play music from my phone over the audio input... 

Can anyone confirm this?

And is there a way to control the input volume?

Thanks and regards 

Seb