The Whirlwind PA-1 is a high-quality, portable stereo headphone amp. It accepts both balanced and unbalanced stereo line level signals through paralleled XLR and 1/4 TRS inputs. A mono/stereo switch allows selection of either stereo or mono operation. In mono mode, two separate inputs can be mixed in conjunction with the balance control. A pad switch attenuates the input -20 dB. It operates on two 9-volt batteries or AC power.