I'm listening to my JH13 with the TTVJ Slim right now, doing some comparisons with my unamped iPod Touch and also my home setup. I have to say the difference between iPod Touch -> JH13 and iPod Touch -> TTVJ Slim -> JH13 to my ears is much smaller than I thought it would be according to the reviews I had read. A bit more bass in quantity, perhaps a slightly expanded left/right image with a tad less congestion, but these differences are all very minor and I'm pretty sure I couldn't tell the difference in a blind test. When I plug the JH13 in my home setup, now that's another game, the improvement is immediate and easily noticeable. I'm a bit disappointed by the TTVJ Slim to be honest, it's kind of reminding me why I stopped caring about portable amps a while ago.