FiiO A1 Silver Portable Headphone Amp A1 Compact design Durable anodised aluminum Chassis Self powered amplifier Can be charged during use Frequency Response: 20~20kHz Earphone Impedance: 16~100 Ohms THD+N: &lt;0.05% (1kHz) SNR: &gt;100dB (A-Weighted) Output Power: &gt;78mW (16 Ohm) Battery: 160mAh, approx. 13H usage Dimensions: 1.65&#034; x 1.57&#034; x 0.37&#034; Weight: 0.71 oz