Dan D'Agostino Momentum monoblock power amplifier
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-funnelshaped holes are machined into the top edge of each side panel to act much as a carburetor venturi, or an air-infusing wine venturibut 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 1Hz200kHz, 1dB, or 20Hz20kHz, ±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 parameterthe 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-endedI 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 itand 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 soundbut how many of you have heard speakers that tonally "disappeared" from wherever in the room you stoodlet 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.