With his former pro-audio background, Ivo LinnenberG's credo is dual differential. Whilst the Allegros have switchable RCA inputs, their XLR are the preferred entry. His output devices of choice are the legendary Hitachi lateral Mosfets of 1977, the only transistor type to ever be made exclusively for audio purposes. In purist mode, that means a single complementary pair; what some clever marketeers elsewhere call single-ended push/pull because two transistors/tubes per channel are the absolute minimum for such a circuit. To achieve an honest 20-bit analog resolution (anything much beyond that disappears in the Johnson/thermal noise of resistors), the Allegro's A-weighted noise is 25μV, thus the equivalent of 120dB of S/N ratio. Attendant harmonic distortion is just 0.004%. The power supply runs off 60.000μF of storage capacitance and a 230VA mains transformer. Input sensitivity is a usefully low 1.5Vrms. Your preamplifier's volume won't max out at barely there. DC offset, thermal and over-current protection are via non-intrusive microprocessor. The astonishing thing? All this packs into a case too small to accommodate the 63A terminal posts, input sockets, power IEC and heat sink on its rear. The cooling ribs thus relocate to the front. As a class A/B circuit, nothing bigger was required. To me, the whole Allegro concept spoke loudly enough to request a review loaner pair. Let's reiterate: petit very practical form factor; reasonable not overkill power with low-impedance stability; top resolution (low noise + low distortion); no signal-path capacitors; no phase shift from insufficient extension (at least 10 x the audible bandwidth, here 0.3Hz-350kHz); high transient speed; high drive current. As Ivo puts it to those who'd correlate small size with small ambitions, "clever construction enabled us to build an amplifier with high packing density, making its signal and power paths extremely short. Creating circuits with unrivalled speed and response time is, amongst other things, a matter of physical closeness of electronic parts. The higher the frequency, the more important it is to reduce every millimeter of board trace." For those of the visual persuasion, Ivo has these graphs.