I give this little amp 4 stars I bughot it for use with my iPod Nano 5g and Sennheiser HD600 headphones. The built-in amp in the iPod is **just** a bit inadequate to drive these headphones well on some albums I needed to crank the volume up all the way, and sometimes that still didn't give me enough volume. For $20 plus shipping, I figured I'd give the FiiO a try. If it didn't work, just return it, right? So it came today, and I gave it a try with some of the problematic tracks on my iPod. First reactions: enough volume boost (barely, but enough) to make the problem tracks listenable, and to drive the HD600 s to more than comfortable levels on most music. I have the volume on the E5 turned up all the way, and use the touch-wheel on the iPod for volume control. Second, despite some other reviews here and elsewhere, there is NO discernable hiss or noise from the FiiO E5, either idle or with music playing. Third: Bass boost works as advertised. If you have phones that don't give you good bass response, this will probably fix your problem. The HD600 s have great low-end, so I'm running the E5 set to the OFF position. Summary: well worth the money, and worth a try if your music player is working too hard to drive your particular headphones, or if you need the bass boost. I detect no degredation of the sound with my iPod. Just for fun, I hooked it up in series with my Home Headroom amp, to see if I could hear a difference yep, the E5 blurs the extraordinarily good sound from the Headroom just a bit. But, then, that's not what it's for, is it? It's NOT a high-end, multi-$$$ amp, just a way to get a bit more performance from your portable music player. For that, it works just fine! The only alternatives would be a CMOY amp from one of the builders on eBay, at two to 3 times the price, or a commercial amp at much greater cost. The E5 is good value for the money, in my book. - 1/2 star for the flimsy interconnect cables, 1/2 star for not having a bit more gain. However, overall, I'm very satisfied. Build quality looks fine. The battery even came charged! Happy listening!