So far I haven't detected any tendency for it to become warm laying flat on a table, where only the top and sides are able to act as heat sinks. One thing I really like about the D1 which is also true of HRT's HeadStreamer (a similar DAC/amp) is that it runs cool. I knew before I ordered the Audioengine D1 that it was small, but when I removed it from the box it looked even smaller - about the size of a deck of cards but 1/3 thicker. Although there were no configurations for me to make the D1 work with my Windows 7-64 computer, the PC volume should be set to maximum and then the D1's volume control knob set to the appropriate listening level. Since the short (24 inch) USB cable that came with the D1 carries only the unprocessed digital signal, and the output to the headphone uses the cable that comes attached (usually) to the headphone, there are no cable issues per se that could potentially degrade the sound.

Due to the high signal-to-noise specs of the PCM 5102, the fact that digital signal is upsampled to 24 bit as well as the added benefit of onboard triple redundancy power source conversion and filtering the HD4 Bluetooth implementation presents impressive low noise and low distortion characteristics with a noticeable improvement over other Bluetooth devices.When I first connected the Audioengine D1 to my computer I was pleasantly surprised that it interfaced perfectly with no configuration effort. The PCM 5102 is used as an upsampling DAC and will pad all bit depths to 24 bit, achieving a higher signal-to-noise ratio and lower noise floor. The HD4 Bluetooth receiver and USB input both utilize the PCM 5102 DAC, widely known for its low-noise and high-fidelity. But with careful signal management circuitry and antenna tuning, we offer a superior solution that has up to 3 times the range of standard Bluetooth for multi-room use, with no degradation in audio quality. Most Bluetooth implementations have very limited range, typically within just one room. High-fidelity Bluetooth aptX HD that really works and sounds great. And even if your phone or tablet does not have aptX HD, the HD4 Bluetooth solution is backwards-compatible with SBC and AAC codecs, as well as standard aptX, so you can wirelessly stream music from any Bluetooth-enabled device and still enjoy all your music. The Bluetooth built into the HD4 powered speakers features aptX HD coding which is an advanced Bluetooth audio codec with very impressive sound.

Audioengine headphone amp