I went to the mailbox yesterday and found the PA2V2 pocket amp by Electric Avenues in my box, and since I was on the way to a local park by foot, I decided to try the little amp with my iPhone and my new Sennheiser Amperior headphone. I was listening to a track called Tainted Love by Soft Cell, a 320k CBR conversion of a WAV file I ripped from the CD - good enough for walkabout listening and then some. When I switched from the iPhone to using the amp (via the LOD cable I carry with me), I was immediately greeted with a larger soundstage and better bass. I wasn't expecting that since I don't generally hear that much difference at home with new amps like the Objective2 or FiiO E17 I purchased previously. I am accustomed to a fairly major difference between the sound of the iPhone and the several desktop DAC/amps I have, but I was surprised at how much improvement I got just from the iPhone's LOD out to the PA2V2's analog input. The PA2V2 amp is enclosed in a high-impact ABS plastic box measuring 2.6 x 2.6 x 1.1 inches high, excluding the volume knob and on-off rocker switch. Unlike some battery-operated amps that aren't very portable in the hand-carry sense, the PA2V2 is very portable. I carried it connected to my iPhone in one hand on my walk to the park, and never felt like I was carrying anything more than a larger phone. I could have used one of the rubber rings I had at home that bond the iPhone to a portable amp such as the FiiO E17, but still my average-size hand had no problem carrying both together. The little black box is sealed on all sides with nicely rounded edges, except the front panel which has the volume knob, on-off switch, DC charging jack, analog input jack, and headphone jack. The analog in and headphone out jacks are the normal 3.5 mm type, but the DC charging jack accomodates a 2 mm plug, which is smaller than the standard stereo 2.5 mm "submini" plugs I'm familiar with. My PA2V2 amp came with the two required NiMH batteries installed and at least partially charged. The estimated play time for fully-charged batteries is 100 hours. Given the small size of the amp and its amazing sound and power output, 100 hours seems highly optimistic, yet thousands of these are in the field and that's the typical experience according to the manufacturer. The photo of the PA2V2 I see on the Electric Avenues website shows a typical wall-wart AC-DC adapter, but I received a USB-to-2mm cable instead, so I'm charging the amp with that cable connected to an Apple USB power adapter. I prefer the USB cable to the wall-wart adapter, and I don't remember now whether I chose that deliberately or whether the PA2V2 is supplied with the USB cable by default. Also included with the amp is a 14 inch cable with 3.5 mm plugs on both ends, for connecting typical music players etc. In my case I use the LOD since it bypasses the volume control and possibly other things that feed the iPhone's headphone out. The Sennheiser Amperior headphone I used for most tests is 18 ohms which is very low, and while I don't have a very high impedance headphone handy, I did try the very inefficient 65-ohm Shure 1840, which played very loudly and distortion-free with the most dynamic tracks I have. Those tracks were downloaded from sites like HDTracks and DownloadsNow as 96 khz WAV files, and converted to 320k CBR MP3's using Foobar2000. While the MP3's don't compare exactly to the original WAV files in certain respects, whether soundstage or "airy" quality etc., the dynamics are essentially the same, so my stress tests should be valid for all reasonable uses of the PA2V2 amp. When I finished my portable tests on my long walk to the park and back, I tried some other tracks that I use to test headphones, particularly the Jimmy Smith recording of Basin Street Blues, which has loud mass horn crescendos that can sound awful on less-than-stellar headphones. The Sennheiser Amperior plays those crescendos adequately on the iPhone, but compared to my desktop amps the iPhone sound is somewhat dull and smeared. With the PA2V2 amp the horns were clearly separated and had excellent tonality. I personally don't regard the term "hi-fi" in any way except High Fidelity, and there are a lot of devices marketed today as hi-fi that simply aren't. The PA2V2 is, big time, and that's an unusually good deal I think for what it costs.