Dan D'Agostino Momentum M400 MxV monoblock power amplifier Measurements

Sidebar 3: Measurements

Before I tested one of the Dan D'Agostino M400 MxV amplifiers, serial number 5879, with my Audio Precision SYS2722, I preconditioned it by following the CEA's recommendation: I ran it at one-eighth the specified power into 8 ohms for 30 minutes. At the end of that time, the side-mounted heatsinks were hot, at 106.1°F (41.2°C), and the top panel was hotter, at 110.5°F (43.7°C). After testing the amplifier at high powers, the temperature of the top panel had risen to 120.4°F/49.1°C. The M400 MxV needs to be well-ventilated.

The D'Agostino's voltage gain was 26.9dB into 8 ohms, and the amplifier preserved absolute polarity (ie, was noninverting). The specified input impedance is 1M ohm. I measured 183k ohms at 20Hz, 152k ohms at 1kHz, and 129k ohms at 20kHz. Though lower than the specified value, these impedances are still usefully high.

Fig.1 Dan D'Agostino M400 MxV, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (blue), 4 ohms (magenta), 2 ohms (red) (0.25dB/vertical div.).

Fig.2 Dan D'Agostino M400 MxV, small-signal 10kHz squarewave into 8 ohms.

The D'Agostino's output impedance was 0.5 ohm at 20Hz and 1kHz, increasing slightly to 0.55 ohm at 20kHz. (These figures include the series impedance of 6' of spaced-pair loudspeaker cable.) The modulation of the amplifier's frequency response, due to the Ohm's law interaction between this source impedance and the impedance of our standard simulated loudspeaker, was small, at ±0.25dB (fig.1, gray trace). The response into an 8 ohm resistive load (fig.1, blue trace) was down by 3dB just above 100kHz, though the increasing output impedance at very high frequencies means that the ultrasonic rolloff into 4 ohms (magenta) and 2 ohms (red) was slightly greater. The M400 MxV's reproduction of a 10kHz squarewave into 8 ohms (fig.2) was superb, with no overshoot or ringing.

Fig.3 Dan D'Agostino M400 MxV, spectrum of 1kHz sinewave, DC–1kHz, at 1W into 8 ohms (blue) and ay 100W into 8 ohms (red) (linear frequency scale).

Measured with the balanced input shorted to ground, the amplifier's unweighted, wideband signal/noise ratio was a very good 79.3dB ref. 1W into 8 ohms. This ratio improved to 81dB when the measurement bandwidth was restricted to 22Hz–22kHz and to 84dB when A-weighted. While spuriae at the 60Hz power-supply frequency and its harmonics were present in the M400 MxV's noisefloor (fig.3), these are negligible at –90dB and below ref. 1W into 8 ohms (blue). As expected, the levels of these spuriae ref. 100W into 8 ohms (red trace) were as much as 20dB lower.

Fig.4 Dan D'Agostino M400 MxV, distortion (%) vs 1kHz continuous output power into 8 ohms.

Fig.5 Dan D'Agostino M400 MxV, distortion (%) vs 1kHz continuous output power into 4 ohms.

The Dan D'Agostino M400 MxV is specified as offering maximum output powers of 400W into 8 ohms, 800W into 4 ohms, and 1600W into 2 ohms (all powers equivalent to 26dBW). With our definition of clipping, which is when the output's percentage of THD+noise reaches 1%, the M400 MxV clipped with a 1kHz signal at 442W into 8 ohms (26.45dBW, fig.4) and at 778W into 4 ohms (25.9dBW, fig.5). The AC wall voltage had dropped from 119.7V with the amplifier idling to 118.7V with the amplifier clipping into 4 ohms, which is why the M400 MxV didn't quite meet its specified power into this load. Similarly, although I measured a clipping power of 1050W into 2 ohms, the wall voltage had dropped to 116V at this power.

Fig.6 Dan D'Agostino M400 MxV, THD+N (%) vs frequency at 20V into: 8 ohms (blue), 4 ohms (magenta), 2 ohms (red).

I examined how the percentage of THD+N changed with frequency at 20V, which is equivalent to 50W into 8 ohms, 100W into 4 ohms, and 200W into 2 ohms. The distortion was low into 8 ohms, with a slight rise in the top of the audioband (fig.6, blue trace), but rose into 4 ohms (magenta) and 2 ohms (red).

Fig.7 Dan D'Agostino M400 MxV, 1kHz waveform at 50W into 8 ohms, 0.029% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.8 Dan D'Agostino M400 MxV, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 8 ohms (linear frequency scale).

Fig.9 Dan D'Agostino M400 MxV, spectrum of 50Hz sinewave, DC–1kHz, at 50W into 4 ohms (linear frequency scale).

The M400 MxV's distortion driving 1kHz at 50W into 8 ohms was predominantly the second harmonic (fig.7), though higher-order harmonics are present at lower levels (fig.8). The third harmonic rose almost to the same level as the second, close to –70dB (0.03%), at the same power into 4 ohms (fig.9) and at 100W into 8 ohms (not shown).


Fig.10 Dan D'Agostino M400 MxV, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 100W peak into 8 ohms (linear frequency scale).

When the M400 MxV drove an equal mix of 19 and 20kHz tones with a peak level of 50W into 8 ohms (fig.10), both the second-order difference product at 1kHz and the higher-order intermodulation products at 18kHz and 21kHz lay at –77dB (0.014%). At the same voltage into 4 ohms, these intermodulation products rose by 7dB, but this is still a respectably low level.

The Dan D'Agostino M400 MxV did well on the test bench, offering very high power with sufficiently low levels of distortion and noise.—John Atkinson

Dan D'Agostino Master Audio Systems
5855 E Surrey Dr.
Cave Creek
AZ 85331
(480) 575-3069

jimtavegia's picture

I do like his comment about distortion as with so many liking tube amps this makes sense to me. It is also true as you review and then measure so not to be swayed by what JA1 finds out.

As hard as this is for me to say, this pair of amps at their price compared to some of the prices we read about at the recent shows that are 6 figures, this pair of amps may be a bargain for those who can afford them, as well as the fact that they look superb.

David Harper's picture

I promised myself some months ago that I wasn't going to troll this forum anymore. And, so far, I have kept this promise. 80K. 2 mono amps.
Bargain. God give me strength.

Anton's picture

Well, entry level integrated amps are now 22,000 dollars, so keeping our betters fed seems to be working!

noamgeller's picture

My youtube channel started to recommend me
Interviews of homeless people in LA and the surroundings...many of those poor souls are truly fascinating, illuminating even. Now stumbling on this article and the sentence contains "bargain" must means that something is really rotten with us humans. Shame, shame on us, truly ):

RobertSlavin's picture

I just want someone from the Dan D'Agostino company to explain why this is a reasonable price for this pair of amplifiers.

The reviewer should have asked the company this question. But Serinus never asks this basic question of the manufacturers of the many expensive products he reviews. Price is a very important consideration in a review of a product but not one he seems to pay attention to.

TJ's picture

Congrats JVS on the successful outcome of your AC rewiring project (!) and thank you for this fine review. As a long time Krell user, I’m always intrigued to see what Mr. D’A is doing next.

As compelling as the SQ of his latest amp must be, I can’t help but wonder how it would compare to an SPL s1200, or even the smaller s800 which I am listening to as I write this. These amps have an interesting gain stage with 120V rails, a minimal number of output transistors in a cascode configuration and exemplary build quality. Their surprising clarity, stage depth and deep bass are even more interesting. Definitely worth a listen if you have the opportunity.

MZKM's picture

The Rotel Michi M8 is more my aesthetic, is <1/5th the price, has less distortion and a ton more wattage.

I would like to see the people for who this aesthetic is for.

Anton's picture

This amp would look perfect in Admiral Harriman Nelson's quarters on the USOS Seaview!

Maybe even better in Captain Nemo's rec room on the Nautilus!

It's got more of a seapunk look than a steampunk, but that is just a matter of nuance!

georgehifi's picture

Doubt any Class-D could ever match this kind of BJT powerhouse.

Real amplification for those nasty hard to drive of speakers which only sound stunning when driven correctly.

Cheers George

Jason Victor Serinus's picture

As I prepare to start coverage of T.H.E. Show on Friday, I see multiple comments about the term "bargain" and scratch my head. This is not a term I used in my review. Nor is it a word that I would ever apply to monoblocks that cost almost $80,000/pair.

Products cost what they cost. Those who can pay the price enjoy them; those who cannot have alternatives. The Rotel Michi, mentioned above, is a product I also reviewed in stereo form and praised highly.

jason victor serinus

Ortofan's picture

... decade, DDMAS did offer an entry-level "bargain" stereo amplifier in their version of a plain, black box. The sole front panel adornment was a copper plate bearing the engraved signature of its creator. The Classic Stereo amp then sold for a mere $13,500.

That model is no longer in the current product line-up. The entry-level stereo amp is now the Progression S350, for about $27K. Apparently, DDMAS customers are unwilling to forgo the fancy chassis and the ostentatious power meter.

haroon's picture

John; kindly explain the distortion spikes that coincided with the zero-crossing points in the signal's waveform. Where is that, "more class-A goodness" in this new version?

John Atkinson's picture
haroon wrote:
John; kindly explain the distortion spikes that coincided with the zero-crossing points in the signal's waveform. Where is that, "more class-A goodness" in this new version?

Yes, the second-harmonic waveform is overlaid with spikes at the sinewave's zero-crossing points, but the level of the distortion is still very low, at 0.029%.

As the Momentum 400 MvX runs very hot, I suspect that the designer adjusted the output stage's bias current to ensure that the amplifier didn't overheat.

John Atkinson
Technical Editor, Stereophile

David Harper's picture

why is this forum so dead? Is it because most people have outgrown interest in audio gear? I'm asking a legitimate question. Or maybe young people just don't understand why anyone would care more about gear than about music? This hobby (if that's what it is) is dying. We are an anachronism. Not that I care. Change is inevitable. But it is an interesting question isn't it.

stereostereo's picture

All questions could be somewhat interesting based on their validity. Maybe you care about the gear more than the music but that has not been my experience based on my audio retail store. At my most recent Woofers and Whiskey event I had over 30 people here between the ages of 15-23. And more than 50 between the ages of 25-40. And the main driver has been overwhelmingly ones love of music. I stress to the industry folk who help me with these events to "just play music and have fun." No discussion of crossovers or woofer materials. And people have really responded and the discussions usually center around The Beatles, Frank Sinatra, Frank Ocean or Frank Zappa. That ain't about a hobby it's about a passion for music. And honestly I have not seen that much change in our industry. Sure the gear has gotten better, prettier, Hi res audio, etc but the one element that has remained constant is our passion for music. And that will never change.

Glotz's picture


Anton's picture

700,000 plus visits per month, dead or not dead?


On the other hand, Audio Science review gets 1.3 million plus.


Absolute Sound, 390,000


I guess the question is how 'lively' qualifies as not 'dead?'

Glotz's picture

And yet no response to your circulation figures as an "I'm wrong, sorry."

If he went to an audio show he would see that the places are jammed with tons of people with a variety of backgrounds and ages... and spending levels.

Time to come out of the house, dude. There's a whole world out there! And it's FUN!