last_sdFrom Audioengine's website:<br /><br />"Will the D1 work with my low-impedance HiFiMAN HE-500 headphones?<br />The D1 includes a headphone amp based around the TI NE5532 low noise opamp. This headphone amp is able to provide low-impedance, high-fidelity audio to a wide range of headphones and supports headphones with impedances from 20 to 300ohms."<br /><br />http://audioengineusa.com/Store/audioengine-d1-faq