The HA-4 is not only a state of the art class A headphone amplifier, it can also be used as a compact high-end pre-amplifier. The design is similar to our top of the range Sapphire DAP-800 and will drive any dynamic headphone. Featuring Sugden VCV circuit and coupled to a pure class A zero feedback mosfet output stage. The HA-4 is unconditionally load stable with a discrete constant voltage series power supply. A high input impedance ensures absolute minimal loss of signal with perfect current gain.