Reference class headphone amplifier with Stereo, Mono, and Dual Mono operation modes. In Stereo mode, the L/R input signal is fed to the left and right earphones while the volume level is set by the Stereo/Left control. The front panel inputs provide simultaneous connection of two headphones in parallel. In Mono mode, the left and right channels are summed, and the resulting mono signal is fed to both the left and right earphones. Again, volume is governed by the Stereo/Left control. In Dual Mono mode, the left and right channels can be used independently with individual level controls for the left and right earphones. The PHDA02 operates with all headphones with an impedance of 8 up to 200 Ohms. Impedance matching is achieved by a specially designed switchable transformer. Uncommon and costly, this solution provides superior performance, dynamic range, and signal- to-noise ratio at all loads. Combo input sockets allow for balanced XLR and unbalanced TS headphone connection while parallel XLR outputs facilitate daisy chaining multiple units. The integrated power supply operates with mains from 100 VAC to 240 VAC. The PHDA02 is equipped with low-noise op amps, and the output amplifiers' discrete power transistors are mounted on heatsinks. Dimensions are 1 U 9.5".