Audiophiles on-the-go probably won’t be able to survive too long without the presence of a trusted amplifier in their portable headphones bundle. Indeed, when using a pair of high-end in-ear-monitors (IEM), it is necessary to have an ample amount of power to drive the earphones to their full potentials. When the headphone-out of your average iPod or MP3 player fails to supply enough power, and most of the time they don’t, a portable amp is called in to feed what the earphones demand before they will truly shine. Canada-based company Practical Devices Corp. offers a newly designed, multi-purpose, portable headphone amplifier, targeting audiophiles and average IEM users alike.





Design and Construction (8.5/10)

The XM5 is Practical Devices’ latest invention. In fact, the XM5 is one of the most feature-packed devices in a credit card size that we have ever come across. Not only is the XM5 a headphone amplifier, but it is also a DAC (digital-to-analog converter) via mini USB. Furthermore, the little gadget features Active CrossFeed, Bass Boost, Treble Boost, Gain Boost, and a 75ohms Mode for low impedance earphones. But there is more! The XM5 also includes an Auto Power Off feature and the option for a fast-charge Lithium-ion battery pack. For more advanced users, Practical Devices also included clear instructions on how to roll op-amps and buffer chips with ease. For now, my article may read like an infomercial, but it’s truly because the XM5 is so jammed with features that not listing them all will diminish the brilliance of its design.

While the look of the XM5 may appear bland, its construction is solid. The aluminium body and the aluminium volume knob make the device seem indestructible. The layout of the buttons and jacks also deserves praises. Despite the need to cramp all those buttons on the front plate, the company manages to do so in a way that is highly access-friendly. The two jacks (Headphone Out & Line-in) also have enough room to allow one of those large 3.5mm to 1/4” adapters. However, if the Headphone jack is moved a bit more to the left, there will be enough room to fit two of those large adapters side by side. Nonetheless, despite these minor details, the construction and design of the XM5 are of high quality.

The Sound [DAC/AMP] - always in price-to-sound ratio - (7.5/10)

via (stock maxed-out upgrade)

PCM2702 (onboard DAC chip)
OPA134 (stock Opamp)
BUF634P (buffering chip)

Headphones: Sennheiser HD595

If you are a regular visitor of this site, you would probably know that my favourite pair of headphones for testing equipment is the HD595. This entry-level audiophile headphone is situated at a rather good equilibrium, sitting in a sweet spot between high and low impedance, between fast and slow, and between a forward and laid-back sound signature. As a result, the phones tend to take on the character of the equipment being fed.

Alright, let’s get to the sound. After 50 hours of burn-in, the sound appears transparent and clean. The output is rather accurate, with very little coloring of the original recordings. The sound signature has an emphasis on upper-mids and treble. Coming from tube amps and warm solid-state equipments, I’d say the sound has a more digital feel to it. That said, however, it doesn’t mean the feel is unpleasant. It simply means the sound has less coloring, more details, and sharper emphases between notes.

Listening to the HD595 through the XM5 was an absolute pleasure. The accuracy of the combo brought out the unique qualities of each song I auditioned. The amp/DAC conveyed emotions as well as accuracy – you will be fully enveloped by the music while being able to detect imperfections in the recording . Although the treble sparkled and handled sibilance very well, a more crystal feel to the highs would have gotten my two thumbs up. With an emphasis on upper-mids, female vocals sounded fantastic while Frank Sinatra sounded a bit cold. The XM5 has plenty of bass. The lows go rather low, but I’d like to see more kicks to the bass. As a result, snare drums don’t sound as articulate. However, if you listen to pop and hip-hop, you will be dazzled by the combination. While the soundstage is not the widest I’ve heard, the headroom is very spacious, and there is more than enough space for vocals to shine.


Headphones: Sennheiser HD600

The XM5 had more than enough power to drive the HD595. When plugging the 300ohm HD600 in, however, the amp seems to show some deficiency in power. It is not that the XM5 won’t provide enough volume to the phones, it is that in comparison, the sound coming from the HD600 seems more compressed and less articulated. Driving the HD600 with the XM5 was not as pleasant, especially the treble, which demonstrated harshness. Now, it is unfair to compare a portable device to stationed equipments, such as the Little Dot MKIII Tube Amplifier. The raw power of the MKIII alone will trump a device which runs on a small Lithium-ion battery.


Headphones: UltimateEars Super.fi 5 IEM

Coupling the XM5 with a pair IEM was more like it! The 75ohm switch proved to be exceptionally useful when powering the 13ohm Super.fi 5. The switch immediately eliminated any hiss associated with high-sensitivity, low-impedance gear.

The sound of the Super.fi 5 combo was reminiscent of the sound from the HD595, only more compressed. The sound wasn’t what I was looking for. The soundstage appeared a bit limited; bass and vocals were not as well articulated. Thin is perhaps a good word to describe the sound in retrospect.


Score Breakdown:

Treble - 7.5/10
Mids - 7.5/10
Bass - 8/10
Soundstage - 8/10







The Sound [AMP] (8.5/10)

via (stock maxed-out upgrade)

AK4396 (External DAC chip: EMU 0404 USB)
OPA134 (stock Opamp)
BUF634P (buffering chip)

Testing all three sets of headphones with EMU’s DAC confirmed the weakness of the XM5’s stock DAC chip. Soundstage appeared more grandeur and open. Compressions of complex passages opened up, and are now much clearer, with better separation of instruments and notes. This was especially true with the Super.fi 5. At various times, I totally forgot I was listening to IEM. Moreover, the sound signature appears more balanced, with a small shift towards the lower-mids. Frank Sinatra sounded warmer, while clarity and details remained. The harshness associated with the HD600’s treble was much more tamed. Overall, I am very impressed with the sound.


Score Breakdown:

Treble - 8.5/10
Mids - 8.5/10
Bass - 8/10
Soundstage - 9/10



Conclusion ( 8 /10)



Who knew such a small device can produce such big sound. The overall sound signature of the XM5 is of the colder end, with a high degree of details and transparency. Coupling it with a warm pair of headphones will give you a very nice sounding combination. Currently, a maxed-out black XM5 (with Lithium Battery and BUF634P Buffer chips) is listed as $326. Is it worth it? Sound wise, a maxed-out XM5 (amp) is even more impressive than the Corda Arietta (desktop) from Meier-Audio. The XM5 can be ranked as one of the top portable amps out there. Based on my memory, the sound of XM5 (amp) can be put into the same category as the more expensive Predator from Ray Samuels Audio, with equally impressive width and depth.

In conclusion, while the DAC of the XM5 is not one of the highest quality chips I’ve seen, it’s sufficient in driving most warmer-sounding headphones. The highlight of the XM5 is its amp function, coupled with the most number of features I’ve seen on a portable amp. If you are looking for a top quality, credit card size device to drive your low-impedance phones, then the XM5 will be an excellent choice.

This article was written by Cecil Lau on December 30, 2008. All rights reserved.