Dan D'Agostino Momentum monoblock power amplifier Page 2

I've heard very fine amplifiers that produced more bass weight, and brighter and sharper high-frequency transients, than the D'Agostinos. I've heard amplifiers that were more billowy in the lower mids, and drier and more reserved in the upper mids. I've heard some that were more polite, some that were more brash. I've heard amplifiers with faster attack and more generous sustain. All of these are noticeable qualities that, once you hear them, you always hear, like it or not—or you work around them with associated gear.

After spending a great deal of time listening to the Momentums, I kept coming back to their overall seamlessness, their tube-like midband delicacy, their bottom-end authority. They fully gripped the Alexandrias' woofers, but with a light, delicate touch timed and executed to produce just the right blend of speed, texture, weight, and tonality. They produced an airy midband effervescence, and a top end that, while not exactly white light, perfectly complemented everything below.

The overall result was the production of an all-enveloping "sonic aether" in which all of the notes swam with equal ease and at just the right time. In short, I heard at home precisely what I'd heard through the Wilson Sashas at CES: pretty much nothing. Or everything.


Overall, the Momentum's sonic personality resembled that of the big darTZeel, though the very top was a bit more reserved, its high-frequency transients somewhat more relaxed, its bass performance ever so slightly less muscular. That, of course, added up to an equally seamless picture, just on a more reserved scale.

In musical terms
In Grant Green's version of "My Favorite Things," from The Complete Quartets with Sonny Clark (2 CDs, Blue Note CDP 8 57194 2), recorded by Rudy Van Gelder and withheld for years in favor of more commercial outings, the guitarist is accompanied by Clark on piano, Sam Jones on bass, and Louis Hayes on drums. It's a more swinging, breezy, jazzified version than Coltrane's better-known one, but Green, probably playing his Gibson hollow-body, whose treble and bass he liked to turn down, liquefies his single-note lines, exuding woody warmth as he fingers the lower half of the fretboard.

The D'Agostino Momentums reproduced Green's warmth, which is the easy part, while preserving the subtle, three-dimensional aura of sound around each pluck that pulses, blooms, and decays with the notes. That's the not-so-easy part—but when it's done correctly it reproduces an aural image of the physical instrument in a stable, three-dimensional space.

A faster, more clinical-sounding amp might emphasize the transient at the expense of the aura; a slower, softer-sounding one might get the aura but fail to cleanly delineate it. Given that choice, I'd go for clinical over mush—but it's better to hear it all correctly drawn. That's what the Momentums did.

There's probably a bit more sparkle to be had from Hayes's cymbals, but the drums otherwise sounded so "together," from floor toms to snare, and the attack and decay were so clean and well organized, that it didn't matter.

That said, you wouldn't want to run a pair of soft- and/or "burnished"-sounding cables between the Momentums and your speakers, unless the latter sound really bright and clinical. These amps need a wide-open path to a perform best. Speaking of wide-open paths, digits were serviced by an MSB Platinum Diamond DAC IV D/A converter, which I'll be packing up and returning after this review. It's easily the best digital sound I've ever heard (footnote 1).

The Meridian (formerly Sooloos) Digital Music Server just served up "Purim," from the Andy Statman Quartet's Between Heaven & Earth: Music of the Jewish Mystics (CD, Shanachie 64079). Statman's clarinet in the right channel, there's a banjo at center left, and the banjo player's foot taps just to his left. You couldn't ask for a clarinet to be drawn in 3D space with any more air or perfection. You might want a bit more bite to the banjo, but again, the seamlessness of this picture, the way the Momentums subtly produced the aether between the two instruments, as well as the space around each, was part of what made the D'Agostinos special—and spatial.

A benchmark recording for me is Endre Hegedüs's Piano Music in a Church (Almost Analog Digital, also available as a digital download from www.toneapearls.com) a live analog recording of solo-piano works by Chopin and Debussy. It's one man at one piano in a stone church: if you like your soundstage layered, the D'Agostinos produced layer after layer after layer of spatial information while retaining remarkable image clarity and authority. Chopin's familiar (if it's familiar to me, it's familiar) Waltz in D-flat Major, Op.64 No.1 ("Minute"), dances across most of the keyboard, punctuated by dynamic thrusts that test the coherent qualities of amps and speakers alike.

Other than through the big darTZeels, I've not heard a more convincing presentation of this recording, whether spatially, dynamically, or harmonically. So stable was the sound picture, regardless of where on the keyboard Hegedüs's fingers were or how intensely he hit the keys, that the sense of being in the audience and seeing the piano in front of me was as convincing as I've ever experienced. I wish someone would license the analog tape and issue this recording on vinyl, so we could revel in the pitch instability, and beat Artur Rubinstein producer Max Wilcox to the punch. (Max, in case you're reading this: You once berated me at Avery Fisher Hall for being a vinyl fanatic.)

Another solo-piano recording that came to life through these amps was Van Dyke Parks's gutsy performance of his difficult-to-play and twice-as-difficult-to-sing "The All Golden," from Moonlighting: Live at The Ash Grove (CD, Warner Bros. 46533-2). (The song originally appeared on his epic Song Cycle, from 1968, which deserves a better-sounding reissue than the one Sundazed managed.) Again, the sense of the nightclub's space, and the way the amps separated yet naturally mixed the sounds of the room and the monitor speakers, was masterful.

But can they rock?
The Beatles' Stereo Vinyl Box Set (14 LPs, EMI 33809) arrived during the review. The D'Agostinos did an expert job of delineating the differences between the first and second UK pressings, the Japanese box, the MoFi box, Toshiba Pro-Use, Capitol original pressings, and CD and USB flash-drive remasterings of Abbey Road (yes, I spent the better part of a day doing this) and this new edition. It was cut from a 44.1kHz master—as Nancy Kerrigan screamed when Tanya Harding whacked her in the knees at the Olympics, "Why? Why? Why?"

But you know what? The equalization job for the new LPs is excellent, and overall, the tonal balance is masterful. But if you want to hear why CDs are simply inadequate, compare the 24-bit USB stick edition to the 16-bit CD. And the new vinyl's top end, even sourced from 24/44.1k, hits a wall that every other vinyl edition easily sails over. But while the Momentums' top end might be said to be ever so slightly reserved, it was nonetheless completely revealing. As I went through the Beatles' catalog with the D'Agostinos, even digitized vinyl was an absolute pleasure. When I listened to some of the most awful and bright rock records in my collection, they sounded awful and bright. And when I played my best rock recordings, they . . . rocked. These amps didn't cover up anything.

Attack, sustain, decay
My favorite trio, and the D'Agostino Momentum, like the darTZeel NHB-458, flat-out nailed it. Attacks were clean and precise, but not artificial or clinical. I heard no artificial edge definition, no emphasis of leading-edge transients. If those fill your excitement cup, look elsewhere—but it's not real detail, and it's not what you hear live. A soft, warm, billowy take on instrumental attacks may be comforting in the short run, but over time it wears thin—or thick, actually. The Momentum may have been ever so slightly on this side of the attack fence, but not by enough for that to be a problem other than in the careful choosing of associated gear.

The Momentum's sustain was generous—as ample and flowing as a great tube amp's, and that's a major achievement for solid-state. Its decay was equally ample, precise, and long-tailed, fading into a natural ambience—not an artificial, antiseptic black never heard in nature.

One test of an audio component is the type of music it makes you want to hear. Looking back at what I listened to for this review, and discounting the recordings I had to play (a lot of Beatles, and a few other records I reviewed for AnalogPlanet.com), the playlist was all over the map. The D'Agostinos didn't do a better job with any particular kind of music, they did a masterful job with all of them.

Driving the big, efficient Wilson Alexandria XLFs, the steam-punk needles of the D'Agostino Momentums' power meters barely budged, no matter what I threw at them. Given their rated power output, they should have little trouble driving speakers of any efficiency or inefficiency, no matter how punishing the load. If their power ratings hold up against John Atkinson's measurements (given who designed these amps, I have no doubt they will), the Momentums like low impedance loads.

I've heard more clinically precise amplifiers, and ones that produced more digital-like black backgrounds, but, other than the darTZeel, none that could produce such a "meaty," well-proportioned, consistently enticing sonic picture.

Dan D'Agostino's Momentum is clearly his best design yet. With the darTZeel NHB-458, it's one of the two most satisfying power amplifiers I've ever heard.

Footnote 1: The MSB was favorably reviewed by Jon Iverson in October 2012.—Ed.
Dan D'Agostino Inc.
139 Steep Hill Road
Weston, CT 06883
(203) 227-9099

RBrooks's picture

Hopefully the purchase price includes a warranty.

dalethorn's picture

One of those rare components where I wouldn't question the price. I was actually surprised to see $55k for a *pair*.

Axiom05's picture

Personally I was quite surprised to see that JA "broke" one unit on the test bench performing a standard preconditioning test. Not what I would classify as a well engineered product. Another component, that for me, falls under the category of "rediculous" and "irrelevant."

MVBC's picture

As suggested by the design, it looks like a cooktop and... acts like one. Perfect in the kitchen!

John Atkinson's picture

axiom05 wrote:
Personally I was quite surprised to see that JA "broke" one unit on the test bench performing a standard preconditioning test. Not what I would classify as a well engineered product.

When the amp was back at the factory, it was dsicosvered that one of the output devices had blown. Dan' D'Agostino soak-tests his amplifiers before shipping, to uncover "infant mortalities"  - one device must have just escaped the testing with its life intact, saving its suicide for my test bench.

Seriously, the preconditioning I perform is very much a worst case for an amplifier with a class-B or class-AB output stage.

John Atkinson

Editor, Stereophile

labjr's picture

I think I saw it at the Willams- Sonoma store in the mall.

soulful.terrain's picture


These monos are simply the most beautiful amplifiers ever made.

itsratso's picture

wow. classic stereophile. one blew up on the bench, the other got hot enough to fry an egg even though the test was dummied down to get it to pass. yet, "This is an amplifier that is as well-engineered as it is beautiful to look at.—John Atkinson". mmm -hmm.

John Atkinson's picture

wow. classic stereophile. one blew up on the bench, the other got hot enough to fry an egg even though the test was dummied down to get it to pass. yet, "This is an amplifier that is as well-engineered as it is beautiful to look at.—John Atkinson". mmm -hmm.

Where we have just one failure, we report that fact but give the product the benefit of the doubt. We have not heard of any other failures of the Momentum.

John Atkinson

Editor, Stereophile

JoeinNC's picture

Seems Stereophile's highest praise is too often given to hideously priced esoterica like this. 

Go ahead. Call me an unsophisticated, mid-fi slob if you want, but an amp with a mid-five figure price tag (even when it works) doesn't impress me as much as one that is well designed and executed within the constraints of a more reasonable budget, even if it doesn't provide the same absolute performance. At the very least, if a company is going to produce an exercise in excess like this, it ought to work.

Even if it does have Dan D'Agostino's name is on it.

Joe8423's picture

He designs this nonsense because there are way more capable folks than him making stuff for discriminating buyers. 

otaku's picture

That's interesting.  Do you ever get two failures?  If so, do they get reported in the magazine or the website?

John Atkinson's picture

Do you ever get two failures?  If so, do they get reported in the magazine or the website?

We report all failures in our reviews, but no, I can't remember when we had 2 failures of the same product.

John Atkinson

Editor, Stereophile

ppgr's picture

First unit blew up, apparently because of a faulty power device. Then why would you cut short on the standard procedure? Isn't it because you feared it would blow up again?


This reminds me of the not-so-good Totem review, where a woofer was apparently fried during the reviewing processblush

John Atkinson's picture

First unit blew up, apparently because of a faulty power device. Then why would you cut short on the standard procedure? Isn't it because you feared it would blow up again?

You're reading too much into this. I didn't want to risk it because if the second sample did fail, there was not enough time for the manufacturer to get another pair of amplifiers to me in time for the review still to appear in the February issue. I wouldn't publish the review without measurements. but if I did have to postpone the review, we had nothing else prepared to fill the space. However, note that the amplifier passed all the subsequent "torture" tests - clipping into 2 ohms, high-power, high-frequency intermodulation -- without breaking, which strongly implies that had I preconditioned it for the full 60 minutes, it would not have failed.

John Atkinson

Editor, Stereophile

rlw's picture

JA even states that he didn't want to risk the 2nd amp going down.  This is nonsense, and does a severe disservice to SP's readers.  He should have tested the 2nd amp exactly as he tested the first and given us the un-varnished results.  To hell with his deadlines, not testing the 2nd amp using the entire battery of tests is just plain dishonest.


John Atkinson's picture

To hell with his deadlines...

Easy for you to say. Magazines are ruled with an iron fist by the calendar. Here is the timeline involved in the preparation of this review:

Tuesday October 30 thru Sunday November 4, the Stereophile office is closed, without power or heat, due to Hurricane Sandy. This delays final production of the January issue, which in turns delays our start on preparing the February issue.

Monday November 12, I ask Michael Fremer if it would be possible for him to move up his Dan D'Agostino Momentum review from the March issue, where it had been planned to appear, to the February issue. This was because 2 other reviews that had been planned for February dropped out due to logistical issues resulting from Hurricane Sandy and other matters. Michael had had the amplifiers for several weeks at that point and had done all of his auditioning. Michael agreed but warned that he would not be able to submit his text nor let me have the amplifiers until after Thanksgiving. We have arranged for a second pair of amplifiers to be shipped to our photographer in Santa Fe for the cover shoot.

Wednesday November 21, Michael sends me his review text a few days earlier  than promised.

Thursday November 22 thru Friday November 23, the Stereophile office is closed for Thanksgiving.

Tuesday November 27, in the morning, I drive to Michael's (100-mile  round trip) to pick up the amplifiers for measurement. In the afternoon, I perform the measurements.

Wednesday November 28, I write up the measurements and add my text to Michael's by-then copy-edited review file. The complete review is sent to our art director for her to design and lay out.

Thursday November 29, the laid-out review is proofed and a preprint is sent to Dan D'Agostino for him to prepare a Manufacturer's Comment.

Friday November 30, the finalized review file is FTP'd to our printer's prepress department.

Saturday December 1 and Sunday December 2, I write up my Arcam review for the February issue. While I had done all my auditioning of this processor, this review was originally scheduled for the March issue but had had to be moved forward a month to replace another review that also had had to be postponed.

Wednesday December 5, the amplifiers are returned to D'Agostino (I had been waiting for the shipping cases).

So please forgive me for the fact that under this pressure, I neglected to redo the preconditioning test on the second sample of the Dan D'Agostino amplifier. With hindsight, yes that would have been the next step, but that's why it's called hindsight.

not testing the 2nd amp using the entire battery of tests is just plain dishonest.

Yet the only reason you know all this is because we told you. How is that "dishonest"?  If we _were_ dishonest, wouldn't it have been easier for us _not_ to mention the problem on the test bench at all? Your accusation doesn't make sense.

And to be pedantically correct, the second sample of the D'Agostino Momentum amplifier was subjected to an "entire battery" of tests. The only shortfall was that the preliminary test was run for 30 minutes not 60. That is not the same thing as my not performing the test at all.

John Atkinson
Editor, Stereophile

tmsorosk's picture

All things considered , I would have been interested to know whether it was a design fault or a faulty part etc . Another test on a second sample may have confirmed which it was . John could have done the second test after all other tests were done so not to hold up the review slated for the February issue .

John Atkinson's picture

John could have done the second test after all other tests were done so not to hold up the review slated for the February issue.

Yes, you are correct. This is what I should have done. Sometimes it's too easy to miss the obvious.

John Atkinson

Editor, Stereophile

Jay Cook's picture

Thanks for admitting that point John.

OK, let’s set aside the issue of the failure.  Let’s say Dan really does have something here.  Yes, it looks cool, but if it really is an advance in fidelity, how many more listeners could enjoy it if the price wasn’t pushed out of their reach by the bling?  How much more affordable could it be in a more basic housing?   After the power supply, the metal work is usually the most expensive part of a piece of gear.

People are bemoaning the demise of brick-and –mortar local hi-end audio dealers, but to have a good representative sample of products these days, demo inventory alone can cost several million dollars, never mind the cost of stock inventory, physical plant overhead, advertising, marketing,  IT, payroll, insurance, etc.  As a thirty-year-plus veteran of the industry, I’ve grown weary of these kinds of products that have turned off many possible consumers to the joys of high quality audio. 

Usually these kinds of products are dressed up to attract well heeled, but naïve nouveau-riche buyers.  Many of these manufacturers tell me they sell very little in the US- their major markets are the newly-wealthy in the middle east and aisa.

So it’s not meant for everyone, we still enjoy reading about it, we can appreciate it even if we can’t afford it, yadda, yadda, yadda.  We don’t need to rehash the kinds of replies that have appeared here for years.  My point is this: if you really have the know-how to produce a superior sounding product, and you love music, why not eliminate unnecessary costs in the product in order to appeal to the greatest number of possible buyers?  If it really is significantly better than the competition, it shouldn’t need the bling to sell, right?

A second point I need to add- I’ve seen far too many “audiophiles” buy electronics and speakers with expensive cosmetics from “high-end” companies, and throw them in rooms that are acoustical nightmares.  Many would be far better off to spend part of their budget on proper acoustic treatment in their rooms, and spend a little less on gear.  A side benefit- higher “WAF”.  Many of the rooms I do have the acoustic treatments and the speakers hidden behind acoustic fabric.  Of course, if you spent as much on your speakers as some paid for their home, it makes it tougher to brag about it if they’re hidden.  For these folks we put in spotlights that let you see the speakers through the fabric when desired.

Ok, thanks for allowing the rant. 

John Atkinson's picture

John Atkinson wrote:
Before I test an amplifier, my usual procedure is to run it at one-third power into 8 ohms for an hour. With a conventional amplifier using a class-A/B output stage, this level results in the maximum heat dissipation in the output devices.

A poster on the Audio Asylum let me know that the FTC changed its preconditioning requirement 15 years ago, apparently under pressure from manufacturers - see www.ecfr.gov and http://www.ftc.gov/os/2000/12/amplifierrulefrn.pdf. The relevant text is "The amplifier shall be preconditioned by simultaneously operating all channels at one-eighth of rated power output for one hour using a sinusoidal wave at a frequency of 1,000 Hz."

This is much less arduous test of an amplifier's ability to withstand thermal stress, and the FTC considered it more representative of typical use. Certainly it is more suited to home theater receivers, with up to 7 channels of amplification within one chassis, where running all 7 channels at 1/3-power for an hour would lead to thermal breakdown. But for high-end, 2-channel amplifiers? I am not convinced.

Perhaps I should do both: precondition the amplifier before the formal testing at 1/8 power for an hour, then run at 1/3 power for an hour after the rest of the testing.


John Atkinson

Editor, Stereophile


tmsorosk's picture

Some may argue that one third power is not a real world condition but I think the fact that most amps that John torture tests do survive , regardless of price , tells us something about the ones that don't . 

One eighth power for an hour dosen't seem like much of a test . Stay with the current way of doing things .

Axiom05's picture

I have to agree that you should not change your testing procedure. For a stereo amp, 1/8 power does not seem like a challenge. While 1/3 power may be overkill, it at least represents a more demanding test that will indicate any problems with the design.

John Atkinson's picture

While 1/3 power may be overkill, it at least represents a more demanding test that will indicate any problems with the design.

Been thinking some more about the the change in the FTC guidelines. A power level of 1/8 maximum sinewave power implies that the amplifier will be used with music having a peak:mean ratio of 9dB, ie, when the peaks are just clipping, the average level of the music, which corresponds to the heating of the output devices, will be 1/8 full power, or -9dB.

This is a fair assumption for classic rock. But if you have been following our writings on the Loudness Wars -- see www.stereophile.com/content/winning-loudness-wars -- you will see that a lot of modern recordings are compressed more than this, with a peak:mean ratio as low as 5dB. If, then, you play the Red Hot Chili Peppers' Californication loud enough that the peaks reach the amplifier's clipping power, the average level of the music will be almost exactly 1/3 power. Play that track for an hour, as can happen at a party, and you have the same situation as the older preconditioning requirement.

John Atkinson

Editor, Stereophile