Thanks for the reply, Manslick but the knob on US-122L controls the output of the LINE OUT and the PHONES aswell, however when something is plugged in the PHONES it mutes the LINE OUT. The reason for asking is that a friend of mine has the US-122mkII and he's been having problem with it. And his interface doesn't mute the line out so I thought that it may be fawlty but perhaps is the mkII designed that way. I don't know. So I thought I ask on this forum.