One of the greatest audio-related inventions of the last 20 years has been the portable headphone amp. If you’ve got butt-kickin’ headphones from companies like AKG, Grado, Etymotic, Sennheiser, Shure, or Ultimate Ears (to name a few), you should seriously listen up: HeadRoom’s Total BitHead (just reduced to $149!) beefs up the sound from any audio source in a way that used to require clunky gear and an AC power source — but in a pocket-size little box that can run on batteries or your computer’s USB port. And it’s got some pretty awesome tricks up its sleeve too.

The Total BitHead measures 3″ wide by 4.5″ long by .75″ thick, and it weighs only 7.5 ounces — that’s just a couple ounces more than an 80GB iPod. The top of the unit is a rubber flap that peels back to reveal a battery compartment for four AAA batteries, as well as a gain switch in case you need to power speakers or very high-impedance headphones.

On the front, there are two 3.5-mm headphone jacks and two switches — one for power, the other for the crossfeed circuit — plus a volume wheel. The back has an analog 3.5-mm line-in jack and a standard USB 2.0 mini port. The internal components are very impressive, and best of all, the high-end DAC that used to cost $70 extra now comes standard.

The package includes three rubber feet and three pairs of Velcro dots so you can mount the BitHead on your laptop or attach your iPod to the BitHead. You also get a short gold-plated 3.5-mm to 3.5-mm cable and a short USB cable for connecting to your computer.

My two favorite features of the Total BitHead are its USB connectivity and its crossfeed circuit. You can plug the unit into your PC or Mac and it will recognize the BitHead and use it as an external USB audio card — which means you effectively get a digital input, in addition to the analog minijack. It would be even nicer if the Total BitHead also had optical and S/PDIF inputs, but since part of the goal was to keep the size and cost down, I can understand why that was left out.

And HeadRoom definitely knows crossfeed circuits; I’ve checked out their higher-end Desktop Amp, and the crossfeed on the BitHead is definitely on a similar level. It essentially changes the soundstage to bring things like vocals and horns more up front; when you’ve been listening to the BitHead with the crossfeed engaged and then turn it off, you’ll get the impression of the “room” flattening out and widening a bit. Either way, the audio is a lot less fatiguing to listen to, and you get a much better sense of space and stereo separation than without an amp.

Some music benefits from the crossfeed more than others — for acoustic jazz (think 50’s/60’s Blue Note era), I prefer it off. Rock and hip-hop both gain a little more oomph with the crossfeed on, and it can help bring soloists to the forefront in classical music. It’s definitely a matter of personal taste, but I can at least vouch for the fact that HeadRoom’s circuit does what it’s supposed to do very well.

I tested the BitHead with a wide variety of headphones (actually, I’ve been using it pretty steadily for about a year), from Shure’s E2c all the way up to AKG K 701’s — and just about everything in between. It takes them all to the next level of sound quality.

Other nice bonuses include dual headphone jacks and solid battery life (30-35 hours on alkalines, much more with lithium batteries). Plus, when you’ve got the BitHead connected to your computer, you can either use it as a bus-powered audio card or you can flip the power switch on and use the unit’s on-board DAC for even cleaner sound.

Like any product, the BitHead has its downsides: You can’t hot-swap batteries as they’re running out like you can with the Core Sound HeadLine. Also, the volume wheel is scratchy when you make adjustments while listening; HeadRoom says this was a necessary compromise. And again, optical/coax or S/PDIF would have been a nice inclusion.

Rarely do I fall in love with a portable audio device to the point where I’m willing to gush about it in print (or online). But the Total Bithead truly deserves it, and I’ve had a high-school crush on it ever since our eyes (okay, my eyes and its LEDs) met from across a room. If you really really really care about sound quality (and have some decent headphones), this is the best $149 you can spend.