Cambridge Audio DacMagic XS
I mentioned above that Cambridge Audio's now-discontinued DacMagic is my reference DAC in my home stereo system, and it continues to impress me after four years of ownership. So I was excited by the company's recent introduction of the $190 DacMagic XS, a small, USB-powered DAC that competes with the other models here. The XS most closely resembles the HRT MicroStreamer — it's a small, black, aluminum box with a Micro-USB input on one end and a 3.5mm headphone jack on the other. On top of the unit are volume-up and -down buttons. A LED glows during playback, with different colors corresponding to 44.1/48 kHz, 88.2/96 kHz, and 176.4/192 kHz sample rates. (Playback of 176.4/192 kHz files requires setting the unit to Class 2 mode by holding the volume buttons for a few seconds. This distinction isn't important on the Mac, but for Windows, Class 2 operation requires the installation of a special driver.)
The importance of impedance for headphone listening
Electricity is a complex thing (literally — it's described using complex numbers), and the interaction of the electrical characteristics of a headphone amplifier and connected headphones, quantified by impedance, can alter the resulting sound. Using devices with compatible impedance ensures that the drivers on a particular set of headphones are properly controlled and that their frequency response isn't altered. A rough rule is that a headphone's impedance should be at least eight times the impedance of the amplifier. However, this estimate isn't universally agreed upon, and low-impedance headphones will still work with the higher impedance amps, though often with flabby bass and altered frequency response.
The MicroStreamer, DacMagic XS, and DragonFly (as well as the previously reviewed Arcam rPAC) have an output impedance of around 0.5 Ohms, so they'll partner well with headphones with impedance of 4 Ohms or higher. This means that these products are suitable for low-impedance headphones such as many in-ear models. The Meridian is rated at about 5 Ohms, making it borderline for use with lower-impedance in-ear models, while the DACport and D3 are rated at 10 Ohms, so they're ideally suited for higher-impedance (80 Ohm or higher) full-size models. (CEntrance can optionally modify the DACport, if you request, to reduce its impedance to 1 Ohm.) But, again, the 8:1 recommendation is just an estimate, so if you're in doubt about a particular pairing, the best thing you can do is test a particular device with your favorite headphones before committing to purchase.
Listening in: DACs alone
In my testing, I found all of these models to be solid performers. If you aren't listening side by side, it's tough to discern major differences — even comparing their performance directly is to some extent splitting hairs. But a review like this is aimed at such comparisons, so let's split some hairs!
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