Pre/Power Amplifiers

One thing is for certain: this amplifier is the most powerful – more accurately, the most load-tolerant – in current hi-fi memory, besting the last-most-powerful amplifier, Musical Fidelity's Tri-Vista kW [HFN Aug '03]. D'Agostino quotes 1.5kW/8ohm doubling to 3kW/4ohm and 6kW/2ohm although we obtained a slightly higher 1.605kW/8ohm and a slightly lower 2.73kW/4ohm. Not that 2.7kW can realistically be described as 'low' for, under dynamic conditions, the Relentless's massive power supply serves up 1.74kW, 3.35kW, 6.36kW and 11.325kW into 8, 4, 2 and 1ohm loads, respectively, the latter equivalent to 106.4A for 10msec at <1% THD [see Graph 1, below]. Yes, over 100A! (D'Agostino quotes '400A peak' but no period, frequency or THD limit is specified). However you look at it, the Relentless will surely drive any high-end loudspeaker without pause (figuratively and literally – neither DC, over-current or thermal protection was tripped during these in-depth lab tests).

Output impedance is close to the specified 0.03ohm at 0.04ohm from 20Hz-10kHz, rising thereafter to 0.06ohm/100kHz and 0.335ohm/100kHz. The frequency response follows suit with a very gentle treble roll-off amounting to –0.5dB/10kHz, –1.1dB/20kHz down to –7.6dB/100kHz (identical in both units) just as distortion hovers at a minimum of 0.0009% at 1W from 5Hz-200Hz, rising very gently to 0.0013%/1kHz, then 0.0035%/10kHz and 0.006%/20kHz [see Graph 2, below]. Versus output, distortion rises very gently indeed, reaching 0.005% through bass and midrange at 100W/8ohm and 0.03% at 1kW/8ohm. Bearing in mind the size of the PSU, noise is low at just –75dBV and the A-wtd S/N wide at 91dB (re. 0dBW). PM