D'Agostino Relentless Mono Power Amplifier Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 106A (!)


Distortion versus extended frequency (1W/8ohm, black; 100W/8ohm, red)

Power output (<1% THD, 8/4ohm) 1605W / 2730W
Dynamic power (<1% THD, 8/4/2/1ohm) 1740W/3350W/6360W/11325W
Output impedance (20Hz–20kHz) 0.039–0.060ohm
Freq. response (20Hz–20kHz/100kHz) +0.0dB to –1.1dB/–7.6dB
Input sensitivity (for 0dBW/1.5kW) 139mV / 5335mV (balanced)
A-wtd S/N ratio (re. 0dBW/1.5kW) 90.7dB / 122.5dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.0025–0.016%
Power consumption (Standy/Idle) 35W / 512W
Dimensions (WHD) / Weight (each) 572x280x826mm / 258kg
Price £125,000 (each)

D'Agostino LLC
Connecticut, USA
Supplied by: Absolute Sounds Ltd
0208 971 3909