Imagine spending a thousand dollars on a pair of speakers and then hooking them up to a boom box. What a waste. Well, that is exactly what is happening when you buy a good pair of headphones and plug them into your average headphone jack. Designers of audio equipment know that the headphone jack is rarely used, so they don't bother to put a good amplifier behind it. (Especially in Portable Units). Such equipment is designed with power conservation in mind, so the headphone jack is designed to put out as little power as possible. Driving a decent pair of headphones with a portable player almost always results in low volume output, and bass that is hardly noticeable and/or clips/distorts very early. In summary, you get Poor overall Dynamics. The fact is that headphones are miniature speakers and require a miniature power amplifier to drive them with fidelity. Headphones provide a complex electro-mechanical load; they may be small, but they still need a power amp with excellent stability and low output impedance to bring out their potential, which even home units don't often achieve!(headroom.headphone.com)
For this reason we have developed the HPA series Portable Headphone Amplifier. Used in between your system of choice and your headphones, you'll hear nuance and detail you've never heard before. The bass will be tooth-rattlingly low and tight, incredibly crisp highs, and sensational midrange; The Dynamics will be delivered. Soundstage quality surrounding you with utmost portability.