A music lover who's also a gadget lover will eventually stumble onto the substantial niche market of headphone amplifiers. YES, the observant among us will note that your receiver, mp3 player, and even laptop already have headphone amps built in, so what's the point? The point is that the headphone amps in these devices are often either of dubious quality, or inadequate for driving high impedance headphones (more than 100 ohms), or difficult to drive ones (lower than 85db sensitivity). There's one other benefit. Relieved of the chore of driving headphones, the battery in your portable device will last longer.
Companies like Headroom ( http://www.headroom.com ), Antique Sound Lab ( http://www.divertech.com/antiquesl.html ), and Musical Fidelity ( http://www.musicalfidelity.com/products/smlx/xcanv8.html ), Grado Labs ( http://www.gradolabs.com/frameset_main.htm ) and others have created and nurtured a cottage industry manufacturing headphone amplifiers for some time now. Headroom can be credited with more or less creating the PORTABLE headphone amplifier market. I have their first portable amp, the Airhead, and it's a great little product. Koss also makes an inexpensive model with a built-in equalizer, the EQ 50 ( http://www.koss.com/koss/kossweb.nsf/p?openform&pc^ac^EQ50 ). While not without faults, one wouldn't expect it to be for the (about) twenty bucks it sells for. It sounds good, and can add "oomph" to, for instance, my portable cd player which has a headphone output that's quite anemic.
Then there's Fiio, a Chinese company that specializes in portable audio devices with tons of value for the money. Their first headphone amp, the E3 didn't have a volume control! The one under review here DOES ( http://www.fiio.com.cn/en/ ) have a volume control. It also has a defeatable bass boost (NON-defeatable in the E3...you either love all that bass, or you don't!), very nice feeling controls...three of them: power, bass boost on and off, as well as the volume control, which is "stepped" via an up/down rocker, NOT adjusted with a rotary potentiomete. The headphone output completes the top panel. On the bottom, there's a line input (connect to the line or headphone output on your device), and a miniature USB connector for recharging the built-in Lithium-Ion battery. On the side there's a permanently attached "belt clip". And other than the company logo, that's it.
The package contains the amplifier, two input cables (long and short), the USB cable (for battery charging), and the instructions. That's it. So let's get to it...how does this thing sound? Well, it does what an amplifier SHOULD do. At low volumes, and with efficient headphones, very little. If your 'phones need some extra bottom, then the bass-boost adds it, without lots of mid-bass "boom". But if you have difficult-to-drive 'phones, like my Sennheiser HD-580s, then things get interesting. These 300 ohm phones are among the most difficult to drive on the market. Most portable devices can't get them above a whisper. The Fiio E5 CAN drive them to a decent level (!), and the bass bosst gives some much-needed "slam" in the bottom two octaves (not THAT much...these ain't "rock 'n roll" cans!) A real improvement for portable listening. Bravo! Still, this wouldn't be MY choice for portable listening...I'd like a little bit more "slam" on the bottom, and the ability to go just prehaps another three to five db louder. Still this makes these phones quite usable with portable devices...which surprised me!
Next up was my much easier to drive Bose on-ear headphones. While these are so sensitive that my Sansa View can drive them to uncomfortable levels on it's own, I was interested to see if the Fiio did anything useful. It did! The highs seemed a tad "smoother" (if the Bose 'phones have a fult, it's perhaps a tad bit too much "sizzle" in the upper mids, which the Fiio smoothed out). Cool! The difference was subtle, but there. The bass boost added more low-end "slam" as well, but since this isn't an area where the Bose 'phones need help, I quickly switched it back off. The ultimate volume available was quite a bit higher with the Fiio than straight out of my Sansa...which I tested by VERY QUICKLY advancing the volume WAY TOO HIGH! Still, with the Bose at least, this is of little importance to anyone not desiring premature hearing loss!
Finally out came the V-Moda "Bass Freq" earbuds. These were the most sensitive of the bunch, and hence needed extra amplification the least. The Fiio didn't really add anything useful...these phones are already a little "over-cooked" in the bass, they definitely didn't benefit from the bass boost! Again I noted a slight "softening" or "smoothing" of the upper mids and highs, but since the V-Modas are a bit recessed in this range anyway, I sure wouldn't buy the amp just for this (if these are your "buds" of choice). My conclusion: if you use very sensitive earbuds (and most fall into that category), you really can do without a headphone amp!
Conclusion: the E5 DOES what it claims! It has the surprising ability to drive even difficult 'phones to useful levels, it DOES add extra available volume (though often not needed0, and it DOES smooth-over the rough edges if your 'phones are a tad too aggressive "on top". Think "tube sweetness". That's right...this thing reminds me of a tube amp. And I mean that in a gOOD WAY!
And did I mention this thing is TINY (see pictures at the Fiio web site). It almost gets lost in a shirt pocket!
Recommendation: JUST BUY IT! I've saved the best for last...this baby is less than 30 (US) dollars INCLUDING SHIPPING! It adds no noise, distortion, or other "nasties" to the audio, and can be quite useful in the situations cited above. Again, JUST BUY THE THING! You won't regret it!