Korg Nu:Tekt HA-S Amplifier Kit, Headphone Amplifier (Kit), Kit for a battery-powered headphone amplifier with Nutube technology, Headphone amplifier to assemble yourself, No soldering required, Tube: Nutube 6P1, Sound shifts via NFB switch (negative feedback), Input / Output: Stereo mini-jack, Volume control, NFB Switch inside the housing, Output impedance: 10 Ohm, Recommended load: 15 Ohms or more, Power supply: 2 x AA Alkaline batteries, Running time: ± 9 hours, Dimensions (W x D x H): 111 x 65 x 29 mm, Weight: 110 g (Without batteries)