One of the best amplifiers ever designed,technically speaking;extremely low distortion,THD and IMD of less than .002% at 1 khz,4/8 ohms,-1db below full output,extreme damping factor of 10,000,signal/noise level of 112 db ASA A-weighted,frequency response 1.3hz-250khz. The sound is accurate,neutral,precise,smooth,rhythmic,and well-paced. It has impeccable timing,excellent coherence throughout and extreme control over the entire frequency range. I would rank it in the top five amplifiers of all time. This is a no nonsense amplifier designed by Martin Grinrod,formerly an aerospace engineer working for Britain's Department of Defense.Though AVI is little known outside of England,there has been a cult-like following of its products in Britain over the years. I replaced my very expensive MBL monoblocks with the AVI s21ma 2.0 and found the AVI to be more musically revealing and correct(pitch accuracy,harmonic quality,amplitude linearity,intensity,rhythm,and duration).