Dan D'Agostino Master Audio Systems Progression M550 monoblock power amplifier

We audiophiles so frequently get caught up in the pursuit of perfection that some have attempted to rebrand high-end audio as "perfectionist audio." But is it even possible for a single piece of audio gear, let alone an entire audio system, to attain perfection when there's no common agreement as to what "perfection" means? It's easier to cue up a Nirvana track than to find the way to audio nirvana.

Nonetheless, the journey toward sonic perfection continues to grip many of us like a Siren who lures sailors to their death with the sweetness of her song. For some who listen closely and steer wisely, however, that death can be more akin to La petite mort than to a dead end.

I like to set sail with people whose sonic values, as manifest in the equipment they design, mirror my own. In the field of amplification, few American designers are more known for the pursuit of a certain vision of perfection than Dan D'Agostino. Over a 40+-year history in audio, which includes founding and serving as CEO and chief engineer of Krell Industries (1980–2009) before moving on to found Dan D'Agostino Master Audio Systems (aka D'Agostino) in mid-2010, Dan (footnote 1) has envisioned, designed, and shepherded the development of a host of solid state amplifiers and other products that have established a benchmark for melding power and speed with sonic beauty, tonal accuracy, and bass response.

Closer to the musical event. . .
"I want to make something that sounds musical—that satisfies and brings me closer to the musical event that's being reproduced," Dan said at the start of a phone chat that also included Senior Engineer Burhan Coskun, who did crucial work on D'Agostino's latest designs. "I've always strived for this goal. The closer I get, the more engrossed I get in making it better.

"Where I am is way farther than I've ever been. With Krell, I never achieved sonically what I've achieved with Dan D'Agostino. Dan D'Agostino is much, much, much more musical and way closer to my sonic goal.

"Our current designs have absolutely nothing in common with what I did at Krell. When I left that company, I wanted to do something in the completely opposite direction. I'm glad in a way that I was asked to leave, because [the move] provided me with the platform that I could use to do the designs I do today. I think that at Krell we got involved in a numbers game: We can do this better because it measures better, and it does this better. It was more about technology than listening. But at D'Agostino, we listen a lot. Listening is the most important thing, not how it measures."

After Dan founded Dan D'Agostino Master Audio Systems, the Momentum monoblocks (footnote 2) led the way in the first half of 2011. D'Agostino subsequently developed three tiers of products: Relentless, Momentum, and Progression. The monoblock amplifier line, topped by the 570lb Relentless monoblocks ($295,000/pair), until recently extended down through the 95lb Momentum M400 ($65,000/pair) to the 125lb Progression Monos ($38,000/pair)—my reference amplifiers since I reviewed them in October 2017. The Progressions are among the best-sounding amps in their price range that have ever graced my system.

The Progression M550
Now the company has replaced the original Progression monos with the fully balanced, 115lb Progression M550 monoblocks ($44,950/pair). The class-AB M550, which requires a 20A power cable, has a new input-stage transistor structure that is claimed to handle a lot more current and provide six times more power, greater thermal stability during power delivery, "perfect" gain matching between the improved high-signal N and P–channel transistors, and an improved high-frequency response that melds lower saturation voltage with higher gain. There's also an upgraded output stage that includes 48 power transistors and a 2000VA power supply transformer with nearly 100,000 microfarads of power supply storage capacitance. Together with a new and far more efficient heatsink design borrowed from the Relentless, these changes enable the Progression M550's transistors to handle a lot more current flow and run hotter than previous devices used by D'Agostino. "We're pushing a lot harder on all the circuits, but our safe operating area has actually gotten bigger," Dan said.


According to Coskun, technological advances in the Progression M550s have made possible what amounts to a "new amplifier" with a higher bias setting. The M550s can remain in class-A for up to the first 100W of their output. When used in a moderately sized room—mine is 16' × 20' with ceilings that flatten out at 9'—the Progression M550s can deliver 550Wpc into 8 ohms, 1100Wpc into 4 ohms, and a whopping 2200Wpc into 2 ohms. Operating in class-A avoids the switching distortion that is an inevitable result of operating in class-B at higher power levels. Yet, because the M550 is a class-AB design, it consumes only 80W at idle (footnote 3). They're not the Relentless monsters, which start at 1500Wpc into 8 ohms and keep doubling down from there, but they are still a significant advance for products presented by a man who has been pursuing what he refers to as "audio pleasure" for his entire career.

"In all my products, I like to put enough class-A in [the output stage] so that at low, low levels, the amplifier maintains its sweet presentation and sounds more musical," Dan explained. "I'm certainly not advocating pure class-A operation, which is very inefficient. The techniques I've developed do not necessitate the use of pure class-A circuitry, because I get a very musical sound without being in class-A all the time and using a tremendous amount of energy and huge heatsinks. Our designs give you the best of high-powered delivery when needed, as well as the sonic accuracy that class-A bias delivers."

Dan told me that if he'd listened to the new Progression M550s when he designed the original Momentum monoblocks 10 or 11 years ago, he would have declared the Progression M550s better. Nonetheless, in the current lineup, price reflects sound quality. "All three amps are very musical," he insisted, "but they're all absolutely different designs that we borrow from [as we upgrade]. If part of a circuit works really well, we will incorporate it into an existing or future design to see if we can improve it.

"The Momentum 400 is definitely another step toward ultimate musicality—it has a mammoth soundstage, sits on a warm palette, and has more harmonic texture to it. We're not upgrading the Relentless; we're kind of in stasis mode because we don't know how to improve it. The Relentless is a completely different-sounding amplifier with a different presentation. It's big and musical with a really solid platform, but it seems as ultradelicate as listening to a small 10W amplifier on a small speaker. The unfortunate thing is that the Relentless is very heavy. It takes a crew to get them in your house. And they're very expensive as amplifiers go.

"We keep looking at the M400 to see how we can improve it, because it's my baby; it's my Phoenix of an amplifier that brought me back as a company. But I don't think you'll see anything migrating from the new Progression M550 into the Momentum, because we borrowed from the Momentum to develop the Progression M550, and we borrowed from the Relentless to make the M400. I guess the same thing happens with automakers."

Several times during our chat, Dan was effusive in his praise for Coskun, his chief engineer. "Now that I have Burhan, who is so astute with circuits, I conceptualize what I want to do," he said. "Then I draw up a circuit and ask him what he thinks. We decide what looks good and where we might try to change it before we make one. After we get it where we like it, we simulate it to make sure it does what it's supposed to do. Then we build the board, and then we listen to it. That's exactly what we did with our new Relentless preamplifier, which will perhaps ship in September. It makes an extraordinary difference to have someone who understands circuitry working with you. I had 11 engineers at Krell, but none was as keen on circuits as Burhan."


What about the conundrum of D'Agostino products that many, including myself, believe sound great yet which do not yield stellar measurements on Technical Editor John Atkinson's equipment? While the D'Agostino website claims that the Progression's "distortion, signal/noise ratio, channel separation, and bandwidth measurements have all improved," that doesn't guarantee that JA1 will find the M550's measurements even close to superb.

Dan responded, "What I always say is that our equipment measures adequately. The measurements are good and respectable. But we're not looking for measurements.

"I use the same Audio Precision gear that John does—mine may be bigger—but I certainly don't use it for listening. Believe me, if I want to make low distortion, there's a whole lot of things I can do. However, in my experience of 40 some years, low distortion never makes it sound better. Ever. Obviously, if you're way high in distortion, it won't sound that good to your ear. But I'm not sure that high distortion measurements have anything to do with anything other than bad sound. The M550s will measure better than the original Progression monoblocks, but just by happenstance. As Burhan will tell you, we use test equipment as a reference, but it's to make sure that the circuits we design work within their envelope completely the way we intended them to."

What the good man intended and what I did
Visually, the biggest change between the old and new Progression is more compact and elegant internal sinks that lessen chassis weight by 10lb. The width is virtually the same, but the M550 is 1.5" longer and 3" taller. The power on/standby switch remains hidden on the bottom front edge, below the large power meter which has adjustable and defeatable green illumination, and the rear panel contains the same 20A power inlet, main-power toggle switch, XLR input, 12V trigger, plus binding posts of different design. The feet are still big, round, gray, easy-to-remove rubber thingees.

When Bill McKiegan, Dan D'Agostino Master Audio Systems president and Dan's long-trusted associate, arrived to help set up the M550s, we placed them on the Grand Prix Monza stands I used for the original Progressions and attached the same Nordost Odin 2 20-amp power cables, XLR interconnects, and speaker cables. I'd previously had long discussions with Dan about power and knew from prior experience that, in my system, amps sound best when plugged into the high-current outlets of my AudioQuest Dragon-powered Niagara 7000 power conditioner.

Footnote 1: To avoid confusion between Dan D'Agostino the man and Dan D'Agostino the company, I'm identifying the former by his first name.

Footnote 2: Later called the Momentum M300.

Footnote 3: For additional information, please see dandagostino.com/products/progression-mono-amplifier.

Dan D'Agostino Master Audio Systems, LLC
5855 E Surrey Dr.
Cave Creek, AZ 85337
(480) 575-3069

Jeffreylee's picture

Let me get this straight. Serinus reviewed a $45,000 pair of amps and didn't notice that one of them wasn't working properly THE ENTIRE TIME? This guy has turned into an ongoing source of embarrassment and if it wasn't for Mike, Herb and Ken I would have canceled my sub strictly because of his incompetence, not to mention his elitism. This review should have been shelved and rewritten, preferably by someone else, until both amps were working properly.

John Atkinson's picture
Jeffreylee wrote:
Let me get this straight. Serinus reviewed a $45,000 pair of amps and didn't notice that one of them wasn't working properly THE ENTIRE TIME?

It's probable that the output-stage bias of one of the amplifiers, slowly drifted while he was using the pair. It was only when he started his auditioning anew with the repositioned Wilson speakers that he noticed the problem with that amplifier.

John Atkinson
Technical Editor, Stereophile

Jeffreylee's picture

With all due respect, that explanation doesn't seem to scan -- unless bias can drift in a matter of minutes. Serinus clearly says that everything was fine until the speakers were moved, which probably took 30 minutes given their size. And then there's D'Agostino's belief that the bias drifted during shipment. Stereophile has always had some writers I trust more than others but this is pretty ridiculous.

John Atkinson's picture
Jeffreylee wrote:
With all due respect, that explanation doesn't seem to scan -- unless bias can drift in a matter of minutes. Serinus clearly says that everything was fine until the speakers were moved, which probably took 30 minutes given their size.

If the bias had slowly drifted during his auditioning, the incremental change in sound quality would have been difficult to perceive. (Think of the "frog in water that is slowly heated" analogy.) It was after the amplifiers were turned on again after the speaker moving that JVS realized that something was not right.

Props to JVS for his honest disclosure.

John Atkinson
Technical Editor, Stereophile

MFK's picture

The second sentence of Jeffreylee's first post nails it. However, we should be grateful for JVS's music choices and reviews. They have led me to a lot of wonderful music that I likely would not have heard otherwise.

Jim Austin's picture

I want to leave the substance of this comment intact, but I dislike the incivility; I've deleted two other comments for precisely this reason. But I can't think of how to perform surgery on your comment while ensuring that it remains your own, so I'll leave it alone. (No promises, though, about future comments.)

I'm also leaving it because it provides a good opportunity to respond.

I believe that a few critical readers, including you, are missing two points. Or maybe it's three. The first is that we're being radically transparent. For good or bad, instead of covering our collective ass, we've left this out there for all to see. The decision here was to present the whole process, good and bad, so that people can judge for themselves.

I think Jason was courageous for putting this out there--these uncivil responses prove that point. Perhaps I was wrong to allow him to do so, and yet I think it was the right thing to do.

After all, he didn't miss the biasing issue. He heard it eventually. Many writers--specifically writers at other publications--would doubtless have reworked the story to make themselves look better. Jason is to be commended for his honesty and--that word again--transparency.

The second point is this: There is no reason to assume that this was an abundantly audible effect. It may have been quite subtle. You weren't there. Neither was I. Such things can easily be swamped by room, stereo, and (other) psychoacoustic effects, especially when listening in stereo. There's a reason that at Harman and some other places it's standard practice to listen to just one speaker. We audition in stereo because that's how people listen to music, but one speaker can easily mask what's happening with the other. It certainly is possible, if not likely, that I could have missed it.

Either way, we told the truth.

Jim Austin, Editor

MatthewT's picture

The harshest critics didn't read, or at least cherry-picked, as it was all there in the article warts and all from the start. JVS takes more crap than anyone, all the more reason for him to write more.

tonykaz's picture

My older brother was a Horn Player for the DSO.

I recall one performance that seemed wonderful to me, I'd heard him practice that music for a Month.
He got a serious ass chewing for missing a few notes which he fully realised and expected.

The Audience never noticed anything amiss. Me included.

People's synapses adapt and adjust.

That is what makes MR.JA's laboratory work so very important.

Tony in Florida

tonykaz's picture

Are you gonna own these Mono Amps ???


Can I buy your old, tired & worn outs ?

I'll send a Wooden Ship builder to pick them up!

Tony in Florid

rickayre's picture

are you gonna trade in your current amps?

tonykaz's picture

I got first dibs on these tired & warn out old pieces of sadness.


I'll give you first right of refusal for a couple thou. $2,000.

I can't quite estimate a Final Sale Price because they once belonged to a Famous Reviewer for the World's greatest Publication.

Expect them to sell for about 125% of original Retail... of course they both will be properly Autographed and accompanied with beautiful Framable Photos .

You'll be getting the bargain of the Century.

Tony in Florida

ps. for a small additional few thousand dollars I'll try to entice both Mr.JA1 & JA2 to Sign em.

pma's picture

The strange distortion vs. amplitude plot that you can see here
speaks for itself - it is a medium biased class AB amplifier with very low feedback factor or no global feedback at all. Then you see the rise of distortion above 1W and a minimum near to 200W, because the crossover area and distortion compared to the high output voltage gets relatively lower. Shame on the designer.

This and similar amplifiers are its own category with "special" customers. They do not care about measurements at all and probably would not hear any problem. John Atkinson stays too much on a polite side in my opinion, this should be clearly condemned how poor is the result.

tabs's picture

I posted something in response to the glaring deficiencies of this equipment, and it very much appears Stereophile staff deleted it. In no way did I use any foul language, and in terms of spirit, I was no more personal in my attack than @Jeffreylee who rightly called JVS an embarrassment and received a reply from JA instead of a deletion.

Jim Austin's picture

... you referred to another forum member as "a cancer."

Jim Austin, Editor

Jim Austin's picture

Your assertion that anyone is "stealing money" from anyone is of course ludicrous. People who buy D'Agostino equipment (and equipment from other expensive brands) do so with eyes wide open and all their faculties about them. I'm sure their enthusiastic customers would be amused at your presumptuousness.

Jim Austin, Editor

partain's picture

" a conspiracy of audiophiles " is at least as good as " a murder of crows " .

Jim Austin's picture

Jim Austin, Editor

thatguy's picture

what causes bias to drift in a new amp?

Jim Austin's picture

Due to the uncivil nature of some of the posts, this article has been closed to further comment.

Jim Austin, Editor