The HH-1 headphone amplifier from Cary Audio is a hybrid design featuring a valve input stage feeding a single-ended MOSFET output stage.  The HH-1 operates in class A mode at all levels and Cary say MOSFETs were chosen as they have sonic characteristics very similar to valves.The Cary HH-1 features a pair of RCA input jacks and a loop-through output pair making it simple to plumb into your existing set up.

Only two stages of amplification are used in the HH-1 for the shortest possible signal path and It is designed to drive headphones with an impedance between 30 and 600 ohms. The 30-second muting circuit prevents any annoying pops and clicks when turning on the HH-1 headphone amplifier, and ensures that the amplifier is fully stabilised before listening.