This is the hybrid vacuum tube amplifier that pairs with any Bluetooth music device to provide superior audio performance. Vacuum tube amplifiers are known to generate warmer, more dynamic tones than transistor-based models because they limit distortion when overloaded, providing better signal-to-noise ratio. The three tubes in this amplifier generate 28 watts per channel of distortion-free signal to a pair of connected speakers (required), adding punch and clarity to high bit-rate MP3s, Apple Lossless, or CD-quality audio played wirelessly from an iPhone, iPad, or iPod touch. The tubes also provide robust bass response by ameliorating the natural acoustic qualities of second and third harmonics for richer sound coloration. A switch on the amplifier's front enables selection between a Bluetooth audio source or two pairs of RCA inputs, allowing play from multiple audio sources, such as a CD player or turntable (requires RCA cables). With volume knob. Four binding posts in the rear connect to your preferred pair of 4-8 Ohm speakers using the included 6'-long speaker cables. Plugs into AC. 7 1/4" Diam. x 5 3/4" H. (8 3/4 lbs.)