Integrated Amplifiers

MxV Integrated (Dig. Module)

To exclude the possibility of driving the MxV Integrated's power amp stage into clipping (albeit unloaded), the digital streaming module was tested via the headphone output. The balanced preamp output cannot be used separately with the power amp stage muted, but this a common oversight. The max. output of the headphone stage is a healthy 6.85Vrms, albeit at a high 263ohm source impedance but, at any output level, the digital module clips with 0dBFs digital inputs resulting in ~0.7% THD. This is significant bearing in mind that much of the modern digital media tested in our HD Downloads section is normalised to 0dBFs. With digital data below 0dBFs, distortion drops away instantly to, for example, 0.004%/1kHz/–1dBFs and lower still to just 0.0004-0.0007% (re. 20Hz-20kHz) over the top 20dB of its dynamic range. While data up to 192kHz is passed without downsampling, lower digital signal levels see a 'step' in THD and linearity at circa –100dBFs that suggests a truncation to 16-/17-bits – something seen with very early USB solutions. The clipping and trunction are clearly revealed in Graph 1, below.

The latter has an impact on the achievable S/N ratio – a sub-16-bit 89dB (A-wtd, re. 0dBFs/2V i/o) in this instance – while the response extension and useful 76dB stopband rejection are functions of D'Agostino's choice of fast, minimum phase digital filter. In practice the line out response reaches –0.4dB/20kHz, –2.0dB/96kHz and –6.1dB/90kHz with 48kHz, 96kHz and 192kHz media files, respectively, these having a dominant influence over the far flatter response of the amplifier itself. Jitter, gratifyingly, is a low ~250psec and inherently PSU-induced in origin [see Graph 2]. PM

D'Agostino MxV Integrated

Up until these 'MxV' revisions, the Momentum Integrated [HFN Dec '14] and later Momentum MLife Integrated [HFN Apr '17] were both rated at 200W/8ohm and 400W/4ohm despite achieving 215W/295W and 255W/365W, respectively. The new MxV Integrated is rated at a higher 250W/8ohm and 500W/4ohm but goes on to deliver 2x275W/8ohm and 2x480W/4ohm even though it retains greater parity with the original Momentum model in its tolerance of very low impedance loads. Under dynamic (music-like) conditions the inaugural amp managed 345W, 635W, 1.07kW and 1.62kW into 8, 4, 2 and 1ohm loads, respectively, while the MxV Integrated offers 340W, 610W, 1.11kW and 1.59kW, respectively [see Graph 1, below]. Bearing in mind the near-decade gap in testing, these figures are essentially identical.

Corrective feedback has been relaxed in the MxV amplifier so distortion is fractionally higher at ~0.2-0.3% (re. 1W, 20Hz-20kHz) but, like other D'Agostino amplifiers, reduces both with warm-up and with increasing power output to, for example, 0.045-0.4% at 100W [also 20Hz-20kHz, see Graph 2]. In this respect, the specified <0.1% THD at 200W output is correct. Again, like other amplifiers in this family, output impedance is a relatively high ~0.35ohm, so while the native response into non-reactive loads is a flat ±0.1dB from 1Hz-25kHz (and just –1.5dB/100kHz), the MxV Integrated's system response will be influenced by the attached loudspeaker load. Once again, D'Agostino's use of a large and very well-screened outboard PSU enables high power and low noise, so the MxV Integrated enjoys an impressive 90.9dB A-wtd S/N ratio (re. 0dBW). PM