D'Agostino Relentless Preamp Preamplifier Lab Report

Lab Report

As we saw with the D'Agostino HD Preamp [HFN Apr '20], the Relentless Preamplifier's watchface dial(s) indicate the available preamp gain rather than absolute level. The 'numbers' and gain are different in this flagship model, however, with '99' representing a default +5.4dB gain in our early sample (+8dB is claimed), '76' being unity (0dB) gain – below which the Relentless Preamplifier operates as an active attenuator. So, '64' delivers –6dB gain (or x0.5) in this instance.

The two controls are synchronised, each rotary encoder switching through a matrix of resistors, but as the top 'bit' was not enabled in this early sample there was no attenuation from '99' down to '86'. The ±0.5dB steps kicked-in from '85' down to '26' (31dB range), with coarser 1.1dB steps to '12' (14dB range) and 2dB steps down to '06' (12dB range). The steps from '05' to '01' ('00' is a relay-switched mute) are less well-defined but represent a range of ~9dB. D'Agostino informs me that the 67dB volume range will be increased to ~75dB and the 86.5dB A-wtd S/N ratio (re. 0dBV) boosted to ~95dB once the anticipated full gain of the Preamplifier is realised.

More importantly, from a sonic viewpoint, the output buffering is more rigidly enforced here, its 2.5ohm source impedance much lower than that achieved by the HD Preamp [red traces, Graph 1] and its ruler-flat (±0.04dB/1Hz-100kHz) response [black trace] unchanged across the entire volume range. Distortion, too, is both very low and 'flatter' vs. frequency at 0.0006-0.0014% (20Hz-20kHz) and 0.002%/40kHz while the HD Preamp offered 0.0003-0.0025% up to 0.011%/40kHz. Note that the 'right' channel had marginally higher THD [Graph 2]. PM


Balanced line freq. resp. (black) and o/p imp. (red) at 0dBV (Relentless, solid; HD Preamp, dashed)


Distortion versus extended frequency at 0dBV (Balanced in/out; left, black; right channel, red)

Maximum output (<1% THD, 47kohm) >24Vrms (Balanced)
Maximum input level (<1% THD) >12Vrms (Balanced)
Output impedance (20Hz–20kHz) 2.4-2.8ohm (Balanced)
Freq. response (20Hz–20kHz/100kHz) +0.0dB to –0.01dB / –0.04dB
Input sensitivity (re. 0dBV) 542mV (Balanced)
A-wtd S/N ratio (re. 0dBV) 86.5dB
Distortion (20Hz-20kHz re. 0dBV) 0.0006–0.0014%
Power consumption 33W (32W standby)
Dimensions (WHD) / Weight (total) 432x349x432mm / 60kg
Price £159,500

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