Dan D'Agostino Momentum monoblock power amplifier

What better way to celebrate the expiration of a noncompetition clause than to debut a product that has no competition? That's what Dan D'Agostino appears to have done with his Momentum monoblock amplifier ($55,000/pair)—his first new product since leaving Krell, the company he cofounded more than 30 years ago.

First shown a year and a half after the split, the Momentum has created something of a sensation in the audio world, due in equal parts to D'Agostino's long history of innovation in the design of high-performance audio circuitry and the amplifier's stunning looks. Visually, the Momentum is a complete break with D'Agostino's previous efforts. Does anything out there right now compete with its gleaming, jewel-like elegance? It manages a high bling factor without ostentation, and while the look has broad aesthetic appeal, enthusiasts of mechanical watches in particular must have been wiping away the drool at first glance. I drooled, and I couldn't care less about watches.

Compact yet powerful
Unlike the often large, boxy Krells of yore, the 5"-high, 95-lb Momentum is remarkably compact for an amplifier rated at 300, 600, or 1200 watts into, respectively, 8, 4, or 2 ohms. While the central power meter dominates the faceplate, the thick copper side panels draw equal attention. And they're bolted to a chassis machined from a single aluminum billet.

In addition to his nearly lifelong dedication to high-performance audio, D'Agostino is a wine enthusiast, a watch collector, and an automobile buff, and he's managed to include elements of each passion into the Momentum's design. The Momentum's large, round, uptilted power meter, with its 19th-century-style needle, is clearly based on classic watch designs, as are the tight tolerances to which the case is machined and assembled, and the seamless fit that challenges you to find a gap or a join, let alone a bolt or screw. Hmmm. Could there be a sonic metaphor there?

Instead of cooling fins, double-funnel–shaped holes are machined into the top edge of each side panel to act much as a carburetor venturi, or an air-infusing wine venturi—but instead of sucking air in to mix it with gasoline or wine, these venturis allow expanding hot air to vent upward, pulling in the cooler air below. The uses of venturis and copper, a far more efficient conductor of heat than the usual aluminum, mean that the Momentum can be both compact and run remarkably cool in class-AB, even when pressed to pump out the power. At idle, it consumes less than 1W.

The low-feedback, fully complementary, balanced design uses 1% metal-film resistors and two dozen 69MHz output transistors in a direct-coupled, discrete, bipolar output circuit with a claimed frequency response of 1Hz–200kHz, –1dB, or 20Hz–20kHz, ±0.1dB. Like darTZeel's NHB-458 ($144,500/pair when reviewed last August)—which it sonically resembles, particularly in its top-to-bottom consistency in every performance parameter—the Momentum is a low-feedback, not a zero-feedback design. I wonder if, like darTZeel designer Hervé Delétraz, Dan D'Agostino has sacrificed the lowest possible level of harmonic-distortion for a slightly higher number more consistent across the audioband, and if he's done likewise with the signal/noise ratio. Both of those claimed specs are good, but, as with the darTZeel, I've seen lower. The specifications listed for the Momentum on D'Agostino's website are scant.


On the rear panel are XLR input and IEC AC jacks, a bayonet fuse holder, toggle switches for meter sensitivity and illumination, 12V trigger jacks, and a pair of custom-machined speaker terminals that don't accept banana plugs. The panel is uncluttered, which made hookup easy, but my system is single-ended—I used RCA-to-XLR adapters. Dan D'Agostino told me that the Momentum "likes" a balanced input signal, but when I tried running it balanced from the MSB Platinum Diamond DAC IV D/A converter's variable output, bypassing my darTZeel NHB-18ns preamplifier, the Momentum needed more drive. Then I remembered: D'Agostino had also told me that his amp is a "low-gain" design. I went back to single-ended.

Warmed up before warm-up
I first heard a pair of Momentums at a Consumer Electronics Show, driving a pair of Wilson Audio Specialties Sasha W/P speakers. Looking at the difficult-to-drive Sashas, I saw not the multiple drivers of a pair of loudspeakers, but a pair of open troughs from which flowed an effortless wall of musical honey.

You could easily turn that into a sticky negative, but that's not how I mean it. When the familiar music required sparkle, the Momentums delivered it—and particularly when there was bass energy, the amps produced weight, authority, and control that allowed the speakers to disappear. We've all experienced speakers that, when we sit before them in the sweet spot, have seemed to vanish as the actual sources of the sound—but how many of you have heard speakers that tonally "disappeared" from wherever in the room you stood—let alone in a hotel room at a hi-fi show?

That's what I heard as I stared down that pair of Sashas driven by Momentums, and I was hardly alone. It was the buzz all over that CES: "Dan is back!" Everyone I talked to mentioned the sound's seamlessness, which was simultaneously ultra-transparent and velvety rich.

That was then. And now?
How can so distinctive- and memorable-sounding a pair of amplifiers have no discernible sonic character? It sounds like an oxymoron. Surely, given more time with them, I could discover their "sound," I thought. Now that I've spent a few months searching, I'm not so sure.

Wilson Audio's Alexandria XLF speakers, which I reviewed last month, are revealing and relatively easy to drive, and about as smooth- and seamless-sounding a pair of speakers as you're likely to hear, so once again: In what follows, will I be describing the sound of the speakers or of the amplifiers?

Fortunately, I've now heard the Alexandrias driven by the Mark Levinson No.53 and Ypsilon Aelius monoblocks (review coming), the darTZeel NHB-458 monos, the Musical Fidelity Titan, and the Music Reference RM-200 Mk.II. I know what these various amps are each contributing to the sound.

Like the big darTZeel NHB-458s, the Momentums had a consistently "just right" quality in every performance parameter, though the overall sound was not precisely the same as the NHBs'. I've heard amplifiers that were faster, leaner, airier, and thus more transparent, in the way that word is usually used.

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