Monoblock power amplifier. Rated at 400W/8ohm
Made by: D’Agostino LLC, Connecticut, USA
Supplied by: Absolute Sounds Ltd
Telephone: 0208 971 3909
Web: www.dagostinoinc.com; www.absolutesounds.com
Price: £90,000 per pair

POWER AMPLIFIER

D’Agostino M400MxVA bigger PSU, more power transistors and a new input/driver stage – all inspired by the‘Relentless experience’ – gives D’Agostino’s M400MxV monoblocks more Momentum!
Review: Ken Kessler Lab: Paul Miller

Avoirdupois aside, Dan D’Agostino
Master Audio Systems’ Momentum
M400MxV monoblock just maybe the least fussy or fiddly power
amp one can aspire to in the extreme
high-end. Of course, something cute andtiny like a PS Audio Sprout [HFN Feb ’15]
or Quad Vena [HFN Jan ’15] can be liftedwith one hand and requires no degrees
in electronics, but that’s ‘real world’ gear.
At £90,000 per pair, the M400MxVs are
as exclusive as it gets, and such a strong
physical presence is de rigueur.
However, that’s as far as high-end excess
goes because these Momentum M400MxVmonoblocks may run warm, but not
fry-an-egg warm [see PM’s boxout, p49].
And while I have never begged for more
power with the Momentum Stereo [HFNAug ’12], the early ones delivering aroundhalf the power of the monoblocks, theM400MxV simply sounds ‘louder’ and more
powerful even when set to the same levels.
Clearly this is the aural manifestation of anamplifier working less hard than another,
the ease in the sound being so readily
discernible that it almost overshadows theother virtues – and they are legion.

and legacy models) as featuring ‘newconcepts, components, and manufacturingtechniques developed and learned
throughout the past decade’. Having
upgraded the original M400s [HFN Oct ’16]
after six years, the MxV status clearly wasn’t
developed in haste, D’Agostino adopting a
Wilsonian attitude toward design stability– infrequent upgrades, but extensive when
undertaken. Even the suffix to identify
them has resonance withthe company’s history:
MxV stands for ‘Mass times
Velocity’, which is thedefinition of Momentum.
As expected, theupgrades are genuinely
comprehensive and muchtrickles down from theresearch undertaken for the flagship
Relentless monoblocks [HFN Mar ’20].
The latter’s fresh front-end circuitry has
been adapted for these Momentum MxVamplifiers, while all major sections – thepower supply, and the input, driver andoutput stages – have been upgraded.
Among the developments are a newtransformer winding pattern credited with

Legacy looks
Visual conditioning, at least for followers
of audiophile fashion, must also be a given– the lacquered copper heatsinks withventuri tunnels, choice of natural- or blackanodised alloy, and Breguet-style dial being
staples of D’Agostino’s amps since thebeginning. So handsome are these greenlit dials that I can’t imagine anyone
opting to dim them. There’s only one
needle per chassis – it’s a monoblock,
after all – but as with other D’Agostino
amps, the scale on this power meter isessentially uncalibrated.
D’Agostino describes the various MxVmodels (updating the M400 and S250,
RIGHT: Massive 2.2kVA toroidal transformer
and 8x12,000µF/120V reservoir cans feed 14
pairs of ON Semiconductor power transistors
mounted onto solid alloy and copper side plates.
Copper slabs are drilled with cooling venturis

Reprinted from Hi-Fi News for global distribution | www.hifinews.co.uk

HFN Aug D'Agostino M400MxV_Reprint.indd 49

the potential for over 50% more current
from the same transformer ‘footprint’ [seePM’s Lab Report, p51], and new transistors
in both the driver and output stages.
What’s described as a new ‘bias stability
circuit’ provides a claimed 50% increase inoperating bias, which may remind readersof Dan D’Agostino’s Krell philosophy ofa lifetime ago, directly expanding its
Class A operation. This, of course (foraudiophiles of a certain,er, bias) might promise acorrelation with improved
sound quality.

‘Ted Nugent’s
fiery guitar workpath
had all the grit, UpgradeNow, the good news.
fuzz and wail’ The MxV upgrades are

retrofittable to earlier
Momentums, including the S200, S250 andM300, but it does require a return to thefactory. The price quoted to upgrade an
M400 to M400MxV status is £29,000 perpair. Before you let out an audible gulp,
please factor in depreciation, the manyyears of usage of your M400s and the fact
the M400MxVs cost around £12,000 more
per pair from new.

Once in place in the listening room –and at 43kg apiece without their optional
stands you may need help – it couldn’t beeasier. Input is via a single XLR for balanced
operation (there’s an RCA-to-XLR adapter
in the box if your preamp doesn’t havebalanced outputs) while the sturdy binding
posts take spade connectors or bare wire.
The only other items on the back [see p51]
are for IEC mains, sockets for remote on/off triggers and a three-way mini-toggle toselect the meter illumination. As before,
on/off is through a soft-touch button
secreted away underneath the front edgeof the fascia.

Petty differences
Luckily for me, years of Momentum Stereo
usage had attuned my ears to the natureof the archetypal ‘D’Agostino amplifier’.
Despite my own predisposition towardvalves, I always found Dan D’Agostino’s
solid-state creations to be as accessibleand ‘ear-friendly’ as the best valve amps, if
slightly less warm. That has changed withthe MxV upgrades, and I am tempted tophone a reader who found the previous
generation of M400s too edgy. Thesesound positively cuddly.
It started with the magnificent Tom
Petty CD collection, ‘Wildflowers’ & AllThe Rest [Warner 093624899112]. Richwith guitars of various textures and Petty’s
distinct, slightly nasal voice, the first
impression was of a deceptively analoguelike warmth which – I swear – made me
think of open-reel tape rather than vinyl.
The title track, despite familiarity to any
Petty devotee, possessed a freshness which
I had to attribute to the amplifiers’ greatest
strength: openness.
It’s worth recalling that, since Day 1,
all Momentum amplifiers have delivered
bottom octave solidity and extension
rivalled by the precious few. Allied to thisARE YOU WARM YET?
With over 400W/8ohm on tap, and some
55A in reserve to support over 3kW into thelowest impedance loads, the M400MxV willpull nearly double that from the wall in use.
Even idling, the rich bias current, together
with other losses, amounts to 77W being sunk into its thick copper and alloy
chassis as waste heat. And this, in tandem with D’Agostino’s relaxed applicationof corrective feedback, means the M400MxV has a very long warm-up time.
When first taken out of standby, a ‘cold’ M400MxV shows a relatively high
0.42% distortion (1kHz/10W/8ohm) but over the first hour or so this reduces to
0.18% [black infill, inset Graph] as the metal mass, and multiple parallel powertransistors, slowly warm up to about 42oC in a 20oC living space. There aremeasurable differences in distortion over the next 12 hours by which time thethermal latency is almost entirely resolved, and the distortion settles out at
0.085%/10W [beneath the Y axis here]. For more, see Lab Report, p51. PM

ABOVE: While the green-illuminated meter– inspired by a watch hand from 1783 – hasbecome D’Agostino’s signature ‘look’, it’sfunction is decorative rather than indicative!

foundation has always been a retrievalof detail which would impress Sherlock
Holmes, while the transient attack acrossthe frequency spectrum has never beenless than fast, smooth and convincing.
Decay has always been correctly
progressive while the three-dimensionalityof the soundstage was always close tothe best of the triode glitterati. What theMomentum amplifiers needed was a touch
more warmth – not that they were ever
too icy or hygienic.

the right stuff
What the MxV upgrade brings to theparty is a removal of any last traces of theartifice often attributed to either
solid-state amplification or digitalsources. It was clear with the Petty
CD and with The Amboy Dukes’
Journey To The Center Of The
Mind [Repertoire REP 4176WZ],
also on CD, that the openness,
speed, clarity and other strengthsof the M400MxV were having theopposite of the anticipated effect:
instead of forcing the listener tohear more of what was wrong withdigital playback, it seemed to be
showcasing what was right. Ted Nugent’s
fiery guitar work on the title track of theDukes’ album had all the grit, fuzz and wailI recalled of the vinyl.
But three revelations, all on tapes,
ensured that the MxV upgrades weregame-changers, such that I cannot wait
to hear what they’ll do to the Momentum
Stereo amplifier I’ve been using for so long.
First were the duets on Vronsky andwww.hifinews.co.uk | Reprinted from Hi-Fi News for global distribution

20/06/2022 15:27

Labreport
D’Agostino M400MXVABOVE: Each mono M400MxV includes an XLR balanced input and single binding
posts for spades or bare cable. Tiny toggle switch sets the meter’s green illumination

Babin’s 176 Keys – Music For
Two Pianos [RCA FTC-2034 open
reel tape]. As ignorant as I am ofclassical music, a real-life piano sat
1.2m away from my left elbow asI typed. The scale and presence
these recordings manifested via theD’Agostino M400MxVs was nothing
short of the truly realistic.
Next came classical from theother end of the dimensional strata,
the orchestral majesty of Handel’s
Royal Fireworks Music [VanguardVTC-1621] with Edmund Appia
conducting the Vienna State Opera
Orchestra. I have no doubt thatmy susceptibility to its charms wasenhanced by my listening sessions
taking place during the weekendof Queen Elizabeth’s 70th Jubilee
celebrations, but the sheer massof the recording filled the room inwidth, breadth, and yes, height.
Arguably, the most stellar element
was the massed brass, heard withsuch clarity and incision that mypossession of a UK passport suddenly
seemed all the more life-enhancing.

Command and conquer
Up to this point, I hadn’t reallycranked up the sound to see if I
could rattle the Wilson Sasha DAWs
[HFN Mar ’19], which responded
to the M400MxVs with such easethat my respect for them increased,even though it had already reacheda state of near-worship. What I
learned via the M400MxVs wasthat the Sasha DAWs were evenmore capable, more commanding
than I had thought when fed a fullorchestra. Imagine taking delivery
of a hypercar and sticking to thespeed limit, followed by a session
on a track to really stretch it. Thisamplifier was proving too addictive.
Then came the third epiphany,an experience so revelatory thatone visitor – from a rival speakerbrand – was driven to say it was

the best sound he had ever heard
in my listening room, and he’s afrequent caller. It was, of course,
the recording which helped, and it
just might be the finest I have everheard, beyond even the soundtrack
to the 1967 Casino Royale or any of
the usual audiophile milestones.

D’Agostino’s inaugural Momentum power amp [HFN Jul ’11] has
evolved through the M400 [HFN Oct ’16] to the M400MxV wehave here, the latter two models rated at 400W/8ohm and bothexceeding this by some margin at 430W/8ohm and 810W/4ohm(M400) and 435W/8ohm and 840W/4ohm (M400MxV). Theirrespective dynamic outputs are very similar too at 475W, 940W,
1775W and 3010W (M400) versus 440W, 845W, 1650W and3050W (M400MxV) into 8, 4, 2 and 1ohm loads, respectively[Graph 1, below]. The 1ohm figure promises a very substantial
55A/10msec current capability at <1% THD indicating what wealready know – the M400MxV will drive any loudspeaker that’s
likely to cross its path even if, in practice, it’s no more powerfulor load tolerant than its predecessor.
The real story behind the M400MxV has less to do with raw
power than D’Agostino’s ‘tuning’ of the amplifier’s input andoutput stage configurations. This version, quite frankly, is simply
more ‘colourful’ and also subjectively more ‘relaxed’ if the figures
are any guide. Specifically, reduced feedback means distortionis higher than the M400’s 0.04-0.17% (20Hz-20kHz/10W) butvery consistent at ~0.05-0.06% through bass and low midrange
over its 400W bandwidth, increasing at HF from 0.25%/1W to
0.75%/10W and 2.2%/100W [all 20kHz/8ohm, see Graph 2]. The
output impedance is also slightly higher too, from ~0.15ohm(M400) to ~0.18ohm here just as the response is ‘sweetened’
from –0.12dB/20kHz and –2.0dB (M400) to –1.1dB/20kHz and–9.7dB/100kHz in the M400MxV. Subsonic bass remains flat to
1Hz but noise – an innocuous white noise – is higher, leading toa reduced 84.0dB A-wtd S/N ratio (re. 0dBW). PM

A new level
Recorded in 1956, Josh White
Comes A-Visitin’ [Livingston Master
Tape Treasury T-1085] captured
the folk-blues legend with a small
group in one of those early stereo
situations where multi-tracking andtoo many microphones were yet to
infect the industry. The sound wasn’t
merely captivating or convincing.
It was mesmerising, the experience
all the more noteworthy because
my fellow listener was an ex-BBC
engineer with a golden ear and four
decades’ worth of pedigree.
We both agreed: a new level
had been reached in realism,authenticity and sheer transparency.
Truly dumbstruck at the recreationof the studio space, the harmonic
overtones on the acoustic
instruments, and the reproductionof White’s voice… I am humbled.

ABOVE: Dynamic power output versus distortion into
8ohm (black trace), 4ohm (red), 2ohm (blue) and1ohm (green) speaker loads. Max. current is 55.2A

HI-FI NEWS VERDICT
Loath as I am to call this ‘the best’(having heard the Relentless),these latest upgrades reassert
the Momentum’s role as a top
contender for the ‘state of theart’ amp. What elevates the MxVover its forebear are greater
openness and transparency,
vividly revealed when heard
side-by-side with its predecessors.
Imagine the silkiness of a 300B
SET, but with bottomless bass andlimitless power. It’s that special.

Sound Quality: 89%
0-------- 100

ABOVE: Distortion vs. extended frequency (5Hz-40kHz;
1W/8ohm, black; 10W, blue & 5Hz-20kHz; 100W, red)HI-FI NEWS SPECIFICATIONSContinuous power (<1% THD, 8/4ohm)

435W / 840W

Dynamic power (<1% THD, 8/4/2/1ohm)

440W / 845W / 1650W / 3050W

Output imp. (20Hz–20kHz/100kHz)

0.175-0.195ohm / 0.275ohm

Freq. response (20Hz–20kHz/100kHz)–0.0dB to –1.12dB/–9.7dB

Input sensitivity (for 0dBW/400W)

126mV / 2525mV (balanced)

A-wtd S/N ratio (0dBW/400W)

84.0dB / 110.0dB

Distortion (20Hz-20kHz, 10W/8ohm)

0.048-0.75%

Power consumption (Idle/rated o/p)

77W / 730W (1W standby)

Dimensions (WHD) / Weight318x133x546mm / 43.1kg (each)www.hifinews.co.uk | Reprinted from Hi-Fi News for global distribution

HFN Aug D'Agostino M400MxV_Reprint.indd 51

20/06/2022 15:27