While the PMA-50's S/PDIF and USB inputs handle hi-res files without downsampling, its analogue input ADC samples at 48kHz only, reducing the response to 20Hz-20kHz ± 1 dB. With digital inputs this extends to +2.5dB/45kHz and -9.8dB/90kHz though with response peaks of +3.9dB/38kHz and +5.6dB/49kHz, respectively, with 96kHz and 192kHz media files into 8ohm. This is a function of many Class D amps where the HF response then typically rolls-off with falling load impedance (here reaching -2.1dB/20kHz into 2ohm). Maximum power output is limited by digital governance that prevents more than 26W being developed into 8ohm and 55W into 4ohm (and 79W/2ohm or 35W/1ohm under dynamic conditions), regardless of analogue/digital input level or volume setting [see Graph 1, below]. As a safety measure it'll prevent high levels of distortion reaching your speakers should a peak level digital input occur at too high a volume setting.
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