The M1-HPA is another ultra-high-value product from Musical Fidelity that"s housed in the same new, half-width M1 chassis as the M1 DAC. It"s exactly one-half the width and the exact height of the British company"s new M3-series products. For those lucky enough to have experienced the gorgeous Class-A AMS-series, you have a pretty good idea what this little honey will sound like: rich, full, and smooth, but with resolution and grip that"s really out of this world. Naturally this all comes along with great technical performance: low noise, flat response... all the things you"ve come to expect from Musical Fidelity. Operating in pure Class A, the HPA"s technical performance is outstanding. Distortion is incredibly low at less than .0005% across the band, frequency response is ruler flat, and noise ratio is exceptional. It has very low output impedance below 1 ohm. A headphone amp"s output impedance is a usually ignored but very important measurement. The HPA"s extraordinarily low output impedance means that it can drive any headphone with complete linearity and low distortion. The vast majority of competitive headphone amplifiers cannot do this because they have much higher output impedance. The M1HPA has two inputs, line and USB. It has two headphone jacks on the front panel and a loop-out facility. Importantly, the M1-HPA also has a variable line output so that it can be used as a very high quality simple line preamplifier.