All the models I tested are essentially plug-and-play: You simply connect the DAC to a USB port and your computer automatically detects the component and routes audio through it. (If your computer doesn't automatically switch audio output to the connected DAC, you can perform the task manually in your OS's audio settings.) If you've got a Mac and you're going to be playing high-resolution audio, you'll also want to configure your Mac for high-resolution playback (though whether high-resolution offers audible improvements is a controversial matter).
With all these models, you set the volume level in your music software (such as iTunes) to maximum to ensure that the DAC gets an unadulterated digital signal. All models except the CEntrance DACport and the Cambridge Audio DACmagic XS use your computer's software volume setting to control the DAC's internal volume. (On my Mac, the default volume-control increments were often too coarse, particularly for sensitive headphones. Holding down the Shift and Option keys while pressing the volume-up or -down key results in quarter-step adjustments.)
The HRT MicroStreamer and Meridian Explorer offer 3.5mm fixed-level line output (for use with speakers or stereos with their own volume control) in addition to the volume-controlled headphone output. You'll want to be sure to not plug your headphones into the line-out port, as the higher output level could damage your headphones, or, worse, your ears. It's easy to do this accidentally, so plastic headphone port caps are a good way to protect your equipment and hearing.
Over the course of my testing, I used each model both during my regular listening sessions, and while auditioning headphones for other reviews. For direct comparisons, I used my full-size home stereo and my two reference headphones: the full-size, open AKG K701 (currently available as the $349 Q701), which is particularly picky about amplification, and the $1099 JH Audio JH13 Pro FreqPhase custom in-ear-canal headphones, which can be difficult to drive due to low impedance. I also compared the DACs to the full-size DAC I use in my home stereo, Cambridge Audio's original DacMagic (discontinued, but $429 when last available; 4.5 of 5 rating).
CEntrance isn't a household name, but the company has long been producing technology for digital-audio interfaces made by other consumer and professional audio companies. CEntrance's $250 DACport, originally released in 2009 (at the much-higher price of $400), is the oldest product here. Its small, simple design — an aluminum tube with a Mini-USB port on one end, a 1/4-inch headphone/line output on the other end, and the rest of the electronics housed in between — made a splash upon its introduction. In the middle of the cylinder is a rubbery, pencil-eraser-like volume knob. The DACport's aluminum shell is substantial, making the device feel like high-end gear. CEntrance also includes a carrying pouch, a USB cable, a belt clip, and a 3.5mm-to1/4-inch headphone adapter. (A $200 DAC-only model, the DACport LX, omits the built-in headphone amplifier and volume control.)
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