Audioengine - D1 24-bit DAC/Headphone Amplifier

Desktop/Portable Digital-to-Analog Converter
Plug and play for Mac or PC, no driver installation required, includes the high-performance headphone amplifier OPA2134.
Built-in audiophile-grade DAC decoder: AKM AK4396, for more delicate sound quality.
USB and optical input
USB powered, no separate power supply required. High-resolution, low-jitter signal transmission for perfect high-definition audio reproduction. Internal DAC (digital-to-analog converter) uses high-performance AK4396.
Recommended headphone impedance range: 10 ohms to 10K ohms