So I got my amp early this morning and I do must that after listening for a hour or so I can say that I am very happy with my purchase. When I compared the sound of the JDS C421 to that of the JDS BB Altoids amp the difference (to my hears) is more than apparent. I do must say that I am more than impressed. Just like the Altoids the bass boast switch adds a very warm bass and at the same time it does not take away from the clarity. The set up I used was Sana fuze, LOD Cable and westone 4's. This Little amp Is just a big upgrade and it really bring my IEM's to life. I still say that the amp needs a little more burning in time but over all I enjoy this amp. This amp is very well built and small (which I personally like) as you can see. All in all I am happy with my new amp.