⌈ DAN D'AGOSTINO is an American company specializing in amplifiers. It was founded in 2009 and is named after its founder, Dan D'Agostino. This audio industry veteran made his debut in 1980 with Krell and the KSA-100 power amplifier. His current business focuses on beautiful devices that combine aluminum and copper in the chassis. ⌋

DAN D'AGOSTINO PRODUCTS cannot be mistaken for any other. Incredibly well-crafted, compact, rather small in size - and yet very heavy - they feature silver chassis, finished with attention to the smallest detail, in which copper heat sinks with characteristic round holes are placed on the sides. A special feature of its designs is a circular green-lit "window" in the middle of the front panel, a somewhat steampunk element, reminiscent of the porthole of Captain Nemo's submarine, and housing VU-meters showing the power output of the device.

Asked by Chris Martens if this design was his creation, he replied:

Completely. When my prospective customers first saw the Momentum (power amplifier - ed.) at audio shows, standing on the floor with its small stand, they asked: "Is this a mock-up? It's not a real amplifier, is it?" - and that was because it was so small. They expected it to be a giant.

⸜ CHRIS MARTENS, Krell Industries and Dan D'Agostino Master Audio System in: Illustrated History of High-End Audio Volume Two: Electronics, edited by Robert Harley, Nextscreen 2015, p. 191.

Such, too, is the fantastic-looking, expensive, and small stereo power amplifier, part of the Momentum series, model S250 MxV. MxV, or mass times velocity, is the equation for the physical quantity that is momentum.

▌ S250 MxV

MODEL S250 MxV is a relatively small device. But quite a heavy one. And that's because almost its entire enterior is occupied by a massive toroidal transformer, and the aluminum and copper chassis is extremely thick. Measuring a mere 317.5 x 54.6 1 x 133.4 mm, the unit puts out 250 watts into an 8 ohm load, doubling the power at 4, delivering an incredible 1000 watts at 2 ohms, if of course you stick to the manufacturer's figures. This means that the amplifier works as an excellent current source, at least in the load range we are interested in.

Materials posted on the company's website say:

The Momentum S250 MxV stereo amplifier delivers the extraordinary sound quality of the Momentum M400 MxV monoblock in a more affordable stereo design.

→ www.DANDAGOSTINO.com, accessed 6.02.2024.

As you can see, the monoblocks came first, and the stereo version came later. What's more, the entire new MxV series is to use technologies developed for the top-of-the-line Relentless Mono Amplifier. This, the manufacturer points out, is to bring solutions from more expensive products at a lower price. As an example, he cites the use of the same copper heat sinks, the same 1% metallized resistors from Dale, the same Sanken power transistors with a 69 MHz cutoff frequency and the same fully complementary balanced configuration.

The tested amplifier is thus a stereo device, with a balanced gain path, equipped only with XLR inputs. The basis of its power supply section is a new, in the manufacturer's words: a "very quiet" transformer of 1800 watts, which has, as we read, almost 50% more output power compared to its predecessor S250, at the same size. The power supply also features a capacitor bank of nearly 100,000 μF.

The output stage was built using new power transistors that were originally chosen for Relentless' flagship monoblocks. As the company assures, they "are among the fastest available," with a cutoff frequency of 69 MHz, making them very fast (it's all about the high signal rise rate). The Momentum S250 MxV uses 26 transistors, in a push-pull configuration working in AB class. This made it possible to reduce the output impedance to 0.12 ohm, despite the fact that, after all, Dan D'Agostino does not use global feedback in his designs.

The thing that is extremely characteristic of this device are the heat sinks. First of all, they are copper, and secondly, that are devoid of the classic "feathers". Instead, they have holes milled in them. The manufacturer refers to them as Venturi Style Heat-sinks, referring, one assumes, to the Bernoulli effect, later used by Giovanni Battista Venturi in an instrument to measure the velocity of a flowing liquid. The idea is that a constriction is made in the middle of the pipe through which it flows, allowing it to flow faster at that point.

I, however, have a different suspicion related to the name Venturi. Maybe it's just my imagination, or....

WHETHER OR NOT THE FORM of Dan D'Agostino amplifiers suits us, it is hard to debate its originality and being "something." Unlike the overwhelming majority of audio products, this is a thoughtful visual design that also serves the technology. The Momentum S250 MxV amplifier has a clearly structured form, with symmetrical divisions and repetitions. In doing so, it has refined all sides, not just the front. It's a departure from the à la Strip (Las Vegas) design - that I'm linking to Venturi - which has been the prevailing style in audio since the 1970s - only the front counts, and what's beyond it doesn't matter.

On the technical side, it also looks very interesting. The tested amplifier uses a new bias current management circuit, which, as the manufacturer explains, ensures constant polarity, "preventing excessive temperatures even at the highest power output to the speakers." And further:

Additional power transistors in the output stage reduce the load on each power transistor individually. By minimizing the load on each individual transistor, the entire output section performs better and more stably. The result is a richer, more dynamic, intimate presentation regardless of musical genre.

⸜ op. cit.

Along with an exceptional power supply and transistors, Dan D'Agostino also pays great attention to heat dissipation. We've already mentioned the heat sinks, so let's add one more thing: each transistor is mounted with two stainless steel fasteners, a rarity among flat-case transistors. D'Agostino does this because "this is the only way to achieve maximum heat transfer to the copper heat sinks." In addition, each transistor is selected, and only specimens "meeting the required specifications" are used in the production of Momentum S250 MxV amplifiers.

As with all D'Agostino devices, the amplification circuit in the tested amplifier was built with transistors, not integrated circuits. Moreover, there are no capacitors in the circuit, so we are talking about DC coupling. This made it possible to achieve very wide frequency response - the manufacturer says it starts at 1 Hz and ends at 200 kHz, with a 3 dB drop at both ends. The amplifier stands on four aluminum feet with rubber pads, but you can buy the original aluminum anti-vibration stand for it. It won’t be cheap though as it come at PLN 11,250.

The Momentum S250 MxV uses the same chassis as previous amplifiers in the series. Already the S200 model could be upgraded to the S250. As a result, all generations of stereo amplifiers included in it can be upgraded to the MxV. The upgrade includes all changes to the amplifier circuitry, while the chassis remains unchanged. Except for one detail: the original Momentum amplifiers get a new 250-watt meter board instead, reflecting the increase in output power.

▌ SOUND

HOW WE LISTENED • The Dan D'Agostino S250 MxV power amplifier was compared to my reference amplifier, the Soulution 710 solid-state power amplifier, and drove Harbeth M40.1 speakers. Preamplification was handled by an Ayon Audio Spheris III tube preamplifier.

Since the S250 MxV features only balanced inputs, and I didn’t want to use some low quality adapters, I used balanced Acoustic Revive Absolute XLR interconnects to connect it to the preamplifier this time. The amplifier was powered by Acoustic Revive Absolute cable (I also tried Harmonix X-DC350M2R Studio Master cable), and the signal to the speakers was supplied by Crystal Cable Da Vinci speaker cable (test → HERE «PL»). The signal source was an Ayon Audio CD-35 HF Edition SACD player and a Lumin T3 file player.

The Dan D'Agostino amplifier is compact enough to fit easily on the top shelf of the Finite Elemente Mk II rack I use.

⸜ RECORDINGS USED FOR THE TEST ⸜ a selection

⸜ TAKESHI INOMATA, The Dialogue, Audio Lab. Record/Octavia Records OVXA-00008, SACD/CD (1977/2001).
⸜ RUDOLF FIRKUSNY, Rudolf Firkusny Plays Schubert, Schumann, Brahms, Sugano Disc SCD-833001, CD (1983).
⸜ JULIE LONDON, Julie is her name. Vol. 1, Liberty Records/EMI Music Japan TOCJ-90014, HQCD (1955/2008).
⸜ JOHN COLTRANE, JOHNNY HARTMAN, John Coltrane & Johnny Hartman, Impulse!/Universal Music LCC UCGQ-9042, „Verve Acoustic Sounds SACD Series 3”, SACD/CD (1963/2023).
⸜ JOHN AMBERCOMBIE, Timeless, ECM Records/Tidal, FLAC 24/192 (1974/2016).
⸜ PET SHOP BOYS, Loneliness, Parlophone Records Limited | 2x Recording Limited/Tidal, SP, FLAC 24/44,1 (2024).
⸜ JEFF BECK, Who Else!, Epic Records | Sony Music Entertainment/Tidal, FLAC MQA Studio 16/44,1 (1999/?).

»«

THE TEST TEND TO GO DIFFERENTLY. In the sense that though their structure is invariable - ultimately a certain type of experience - yet the realization with specific albums can change from minute to minute. It is often the case that it is the devices in the test that guide me, "telling" me to choose these or other discs. This is a subconscious action, although it has a solid "here and now" basis. This was also the case with the first CD I chose for the Dan D'Agostino amplifier.

The The Dialogue by Mr. TAKESHI INOMATA, Japanese jazz drummer and leader of many bands, is one of the most dynamic and one of the best recorded albums I know and have. It was recorded in the natural space of Tokyo's Lino Hall and is a recording of the drummer's joint sessions with his guests, equally well-known jazz musicians from Japan at the time (this is 1977).

I didn't wait long, and I usually start my listening with the guitar dialogue ˻ 1 ˺, after which I move on to the drums and double bass ˻ 2 ˺ to end with two drum sets ˻ 3 ˺ to hear what the new amplifier is all about, and how much this sound has changed from what the company started with these several years ago.

It is, above all, incredibly resolving sound. A thing I've found somewhat lacking in this company's amplifiers over the years, here it's reached an excellent level. Not that it truly hurt the older models performance in any way, they had other advantages and sounded great, but the S250 MxV is exceptional in this respect. It's as if the increase in output power and power supply efficiency, plus changes in the circuitry, have led to a kind of breakthrough.

For the tested amplifier brilliantly showed not so much the instruments themselves - that's obvious - but the spatial relations between them, the tension between the musicians. I could almost "see" the glances they cast at each other, suggesting who was taking the lead and when, and who was hiding for a moment. I had the impression as if Mr. Okihiko Sugano, responsible for this recording, had brought the microphones a little closer to the instruments - so their own sound could be heard more clearly But after all, the acoustics also benefited from this, so it wasn't a matter of bringing the instruments closer to me.

Because a close perspective, a warm perspective I might add, was the domain of the company's older amplifiers. I liked this sound, I did, and the listening comfort was extremely high thanks to it, but there was nevertheless a distinct own character of the device. Here, too, something of that remains, because it is not a bright sound, but nevertheless the insight into the recording, the selectivity of the sound and - this is important - the dynamics are from a completely different level. And that's why it can seem even warmer than in previous amps.

It also offers a significantly better sound differentiation. Specially for this angle, I listened to Mr. Sugano's recording from 1983: RUDOLF FIRKUSNY Rudolf Firkusny Plays Schubert, Schumann, Brahms. The recording was made directly to stereo tape, like the previous album, but this time to a digital U-matic (16/44.1). You can immediately hear that this is a different space - more intimate, more heavily attenuated. But you can also hear that the trebles are a bit brighter, less sonorous than before. What has been done here with the digital medium is amazing, yet the analog recordings of this outstanding mixing and sound engineer were better.

So I went back to analog recordings. Released in 1955, and reissued by EMI Music Japan in 2008 on HQCD, this is an excellent example of how to record a voice. The singer is accompanied only by jazz electric guitar and double bass, so most of the time we have her in the foreground. The amplifier showed very nicely that this digital reissue is much brighter than the vinyl original from which I usually play it. It's mainly about emphasizing a few kHz in London's voice. An older amplifier from this company would try to make it slightly softer, to cover it up, while the new one didn't hide anything, showing it in a much truer way.

For the S250 MxV did something special. It showed the recording as it - so it seems - actually is, i.e. with emphasized upper midrange, but without unpleasant consequences, superbly saturated the bottom end with energy, let the guitar sound decay, despite the fact that it is, after all, a remaster of the mono version, and therefore more difficult to selectively show the sound sources.

Listening to this album with the American amplifier it will be easier to understand where such brightening came from. And that's because sound engineers often recorded master tapes with the treble raised in order to compensate for the loss of treble when making the cut, and then the stamper and finally - the pressing. As you can see, these were big losses. That's why remastering older 1:1 tapes sometimes brings disappointments, and why I so appreciate what the Acoustic Sounds label is currently doing with its "Verve Acoustic Sounds SACD" series for Universal Music Japan.

So it was a natural step to reach for one of his records. JOHNY HARTMAN'S vocals on the disc recorded with JOHN COLTRANE were warm, big, but also characteristic of the recording. And it was all about the rather strong immersion of it in dark reverb. The tested amplifier can show such things effortlessly. It plays in an organic way, so the sound is natural and pleasant with it, even friendly. But it is also strongly differentiated and open - the reference amplifier, the Soulution 710 (!) plays noticeably lower.

So you could clearly hear the noise accompanying these recordings. Very low with Mr. Sugano's records, stronger with London, here it was really strong. But it was not annoying. That's why when Coltrane enters in the recordings from the aforementioned album, it's a somewhat soft sensual entrance. The musician plays like that here. It's an album reminiscent of the style we know from his - released in the same year - disc Ballads (1963). And this noise was clear with the tested amplifier in its presence, and in how it relates to usable sound. I could almost "see" the tape recorder the material was recorded on.

It's high time to say that the amplifier we're talking about cuts out the space between the speakers from the listening room and puts a new one of its own there. It's a heavily saturated presentation, where the panorama is continuous and everywhere equally dense, one might even say thick. It's wide playing, though the listener's attention is focused on the axis. And that's because the sound is built far into the stage. So there's a lot going on there, hence the perspective.

This is the case even when the instruments are spread extremely wide across the channels, as on Coltrane and Hartman's album, and also when we have a natural, stereo perspective in front of us, as on JOHN ABERCROMBIE's album Timeless. This is the guitarist's first album recorded for the ECM label. Recorded over two days in 1974, it is a wonderful combination of guitar sounds, Jack DeJohnette's delicate percussion and various types of organ. As John Hammer, who played them, said, it was the most beautiful collection of this type of instrument he had encountered to date.

But to the point - the opening title track ˻ 1 ˺ begins gently with the sound of the organ, which then goes extremely low. It was here that I heard Dan D'Agostino's "new" sound give a stronger midrange image. Which can be associated with warmth. There is no longer such a strong saturation of the mid-bass breakthrough, and our attention is focused on much more detail, detail, nuance than before.

Therefore, with this album you could hear more strongly what Hammer is playing in the higher parts, and you could also hear the leader's guitar more clearly than the low, meaty bass. The percussion was also marked. Once again, the outstanding dynamics and speed of this unit made itself known, as the kich drum was incredibly natural and "present." I had heard this before, with Inomata's The Dialogue, but here it appealed to me even more strongly.

At the very end, I played myself the new single by PET SHOP BOYS from their scheduled April 16th release Nonetheless, a track titled Loneliness. With an American amplifier, the rhythmic structure of the track was emphasized, its monophonic, electronically generated bass on the listening axis and percussive elements giving the whole thing "momentum". I had everything I mentioned earlier, that is, a thorough insight into the recording, but also excellent pace.

▌ Summary

THE MOMENTUM SERIES'S S250 MxV amplifier offers perfectly controlled, "wide" sound. Wide in the sense in which the word is used by musicians and studio people, that is, with panache, both in terms of dynamics and panorama, or the feeling of interacting with a real event that almost "crushes" us. We have this both when listening to studio recordings, even intimate ones like Julie London's, and concert recordings - let me cite ˻ 3 ˺ Brush With The Blues by JEFF BECK from his album Who Else!.

The device is incredibly resolving and brings plenty of detail. And it seems warmer at the same time. So it's quite noticeably different from what the manufacturer offered just a few years ago. Now it is impossible to listen to music in the background, because the energy of the sound is so high that it draws our attention, does not allow us to focus on anything else. The device perfectly controlled Harbeth's difficult speakers in this regard, which, at its size, is particularly noteworthy. It keeps the bass under control, regardless of how it was generated and released. This is a top high-end for those who listen to music actively and who would like to know as much as possible about it. A great example of top engineering.

▌ DESIGN

AS I SAID, the form of the amplifier is original and is "something to remember". It is formed by reflective surfaces of aluminum and copper, that is, by the contrast between cold and warm light. And then there is the green back-lighting of the VU Meter, reminiscent of the dial face of a high-end Swiss watch. This back-lighting, we should add, can be turned off with a small switch on the back panel. The heat sinks are made of copper, as well as is the chassis. Aluminum is the rest of the walls - it's milled from a single, large piece of aluminum. The exception is the bottom wall, with a smaller thickness.

The aforementioned "porthole" is the only element of the front panel. The indicators are shaped like the hands of a watch. Although they are said to be "output power meters," I would treat them more as an ornament. One, that they are VU-meters, i.e. meters of input voltage, not of output power, and two, that they are not graduated. But it's an ornament of exceptional taste. On the back, in the sub-fret, there are two pairs of gold-plated speaker jacks, two XLR inputs and three jacks for remote control; there's also an EIC power socket. The standby switch is located on the bottom panel, right at the front edge, which reminded me of the solution used by Ayon Audio for years.

Because the device has inverted proportions, that is, it is deep and narrow, the components on the rear panel are placed close to each other and not particularly convenient to use. And yes, the speaker jacks accept only spades and bare wires. But if we want to use the spades, we have to plug them in from the top, thus significantly bending the cable. It's impossible to connect them from the top, because the way is blocked there by interconnect plugs. The release latches for the male interconnect plug are just below the speaker jacks and are very difficult to operate. And only the power cable can be plugged in without any problems.

Almost the entire interior of the unit is occupied by a mighty toroidal transformer with multiple secondary windings; there is a separate transformer for the standby section. Along with the power supply components, the main transformer is bolted "on its back", to a copper plate, and the latter to an aluminum chassis. Eight large mains ripple filter capacitors of 12,000 μF each work with it. Other sections of the power supply, including the stabilized one for the input transistors and control circuits, are on a separate board.

The input and control section received a separate board and is a discrete circuit. This is a completely new board, and it owes most to the top-of-the-line Relentless series. Now the transistors are surface-mounted, as are most of the capacitors, and only the Dale resistors are mounted through-hole. The manufacturer says the signal path has been shortened and ground has been optimized.

Another change is the protection circuits, now located outside the power path. In the S250, these were thermistors that applied higher and higher voltages as they heated up. Their disadvantage was that they were constantly in the power supply path and always represented some resistance. Now the power supply works with two relays that continue to give voltage a moment after the power is turned on. Since their contacts have negligible resistance, this allows better energy transfer than before, mainly transients.

As we read in Mohammed Samji's report for the Part-Time Audiophile website, the biggest changes took place with the circuit with output transistors. Dan D'Agostino said at the time:

“In terms of the new output stage, let’s just say that we have increased to more drivers, faster recovery times, and more control over the output transistors over what we have traditionally done in the past.”. (...)

A capacitor/resistor network connected to the base of each transistor ensures stability even at high frequencies and with low-impedance speakers. Additionally, every output transistor is measured, and only devices that match the required performance specifications are included in the production of Momentum S250 MxV amplifiers.”

⸜ Part-Time Audiophile, → PARTTIMEAUDIOPHILE.com HERE, accessed 8.02.2024).

Plates on which we find only resistors and capacitors working together with bipolar output transistors were screwed onto the heat sinks. They work in a push-pull mode in class AB. They are complementary NJW3281G + NJW1302G pairs from Onsemi. The entire circuit is fully balanced, which means that both speaker terminals are "live" and no ground or circuits of this type are allowed to be connected to them.

Looking at the construction of the amplifier, you can see that it is the result of years of engineering experience and that they did not spare any expense here. ●

▌ Technical data (acc to the manufacturer)

Nominal output power: 250 W/8 Ω, 500 W/4 Ω, 1000 W/2 Ω
Frequency response: 1 Hz- 200 kHz (-1 dB, 20 Hz-20 kHz, ±0.1 dB)
Signal-to-noise ratio: 105 dB (unweighted)
Input impedance: 1 MΩ
Output impedance: 0.12 Ω
Total harmonic distortion (THD): 0.1% (250 W/8 ohm, 1 kHz)
Dimensions (W x H x D): 317.5 x 54.6 1 x 133.4 mm
Finish: silver or black, other colors - on request

THIS TEST HAS BEEN DESIGNED ACCORDING TO THE GUIDELINES adopted by the Association of International Audiophile Publications, an international audio press association concerned with ethical and professional standards in our industry, of which HIGH FIDELITY is a founding member. More about the association and its constituent titles → HERE.

→ www.AIAP-online.org