Douk Audio 2P2+VMOS Class A Hybrid Tube Amp Headphone Amplifier USB DAC HiFi Pre-Amplifier This is a hybrid integrated amplifier, can do as Tube Amp & Headphone Amplifier & USB DAC & Pre-Amplifier. Direct heat tube 2P2 + VMOS solid state circuit structure, the output stage "A" class output, high current output, all of this make the amp have transparent sound, powerful bass, good strength and control, alomost no background noise. Perfect sound + delicate appearance: Hi-end body, HiFi components and perfect layout, it's the high-grade fashion choices.USB DAC Part: Receiver chip and a separate decoder chip (CM108 + TDA1305T), Support USB2.0 high speed transmission Apply sound source: CD, MD, Phone, MP3, MP4, Ipod etc. Support system: Win 2K, Win XP, Vista, Win 7 (32/64), WIN8, Mac OS X. OTG: Can direct used in the phone with OTG function. This amp is Class A output with high current, the shell temperature maybe a little high when prolonged use, it's normal and will not affect the product performance or sound, please try to put it in the place of good ventilation and heat dissipation. Notice:Since the output power of this headphone amplifier is a little low,it is a good fit for headphones with low impedance such like Sony(Recommend impedance range is 0-50ohm).It is not suitable for headhones with high impedance or high power.