shipped in original packaging to US48. This A-100 amplifier has handled Sennheiser high impedance cans(800, 820, 650), Hifiman HE-500s, and T-50RP headphones. It has also driven KEF LS50s and Emotiva B1s with ease. It delivers 50 watts per channel into 8 Ohms and 80 Watts per channel into 4 Ohms. This model uses a toroidal transformer. The headphone output has two options: Series resistors to reduce the output to a normal level for most headphones, and a full power mode for low efficiency planars and high impedance headphones (*see warning on page 11 picture attached below). Switching between the two modes requires adding jumpers to an internal board. The amp is shipped in low power headphone mode, the jumpers are in a bag with the accessories. The volume controls both headphones and speakers, but the speaker output is shut off when headphones are connected. The RCA connections on the back are loop-through (any output would not be controlled by the front volume knob). One screw on the side and one screw on the rear are missing. This has been one of my favorite audio acquisitions. I am selling because my hearing isn't what it was 5 or 10 years ago.