Up until a couple of weeks ago, I had never heard of a headphone amp. Well, I guess part of the reason is that I never owned a good pair of phones. I recently bought a pair ofSennheiser HD-595 Premier Headphone(here on Amazon), which are tight (see my review). The Senns have pretty high impedance (50 ohms), and my netbook and ipod don't have enough juice to power it. Therefore, the need for a headphone amp arose.One of the first HP amps that I came across was the FiiO F5. I had never heard of this brand. I think a reviewer mentioned that its Chinese. Anyhoo, The features that hooked me was its price, size(it's the same size as the iPod shuffle), and simplicity. Seeing a majority of positive reviews, I decided to go for it. I received it in 3 days from Head-Direct (which I would recommend since it was under $25 with shipping, and they use Amazon for payment).Upon first trial through my iPod, I was a little miffed because there was a high frequency "noise", is the best way I can describe it. But it went away when I played the music, and it never recurred. I played music with, and without the amp, and the difference is quite remarkable. With thew FiiO connected, aside from a big boost in volume, the depth is also enhanced. The bass boost is subtle, but noticable. I would recommend maxing out the volume on the amp and controlling the volume from the source, as the button is quite small and right next to the output plug.Other than the sound, the things I like about it is its size, internal rechargeable battery, on/off button, clip, and blue/red  light, which indicates when it is on/off or charging/charged. It also comes with a 6" and 3' cord, and a USB to mini USB charging cable.The only things I can think of that I don't like is the fact that it charges through the computer, which means that, 1) you need access to a computer, and 2) the computer has to be on. I also find it a little disturbing that the instruction manual states that the battery can be charged and discharged hundreds of times, BUT the battery will eventually wear out and is irreplaceable. Hopefully, it will last 25 bucks worth of charges! Which brings me to question how long the charge will last. And since I just got it, I have yet to figure that out. Highly recommend it. 

Question: How does build quality work?
Answer: Up until a couple of weeks ago