Genuine National JDSLABS Objective2 Black Edition By NwAvGuy Headphone Amplifier JDS LABS (Made in USA) Gain: 2.5x and 6.5x Frequency Response: +0.01, -0.01 dB (20Hz-20kHz) Output impedance:0.5 ohm Volume Potentiometer Taper: 15A or 3B Power:14-20V AC adapter with a standard 5.5 x 2.1 mm(not DC adapter). You can charge 9V battery inside from AC Jack and carry this amp. Size: 108.50 x 80.00 29.50 x mm Weight: 311g Accessories: cleat rubber/adapter