PrimaLuna EVO 400 Tube Integrated Amplifier - EX DEMOHEADPHONE AMPLIFIER One of the best headphone amps in the world. And the only amp that lets you listen with either the warmth of Triode or the wide bandwidth of Ultra linear operation at the push of a button! Most tube integrated amps and preamps use a solid state op amp chip for running headphones. Stand alone tube headphone amps will vary in quality like any other tube amp. Headphones are simply small speakers that require less power. Some amps will