Conrad-Johnson • MF-2550 SE Stereo Amplifier

by Vance Hiner | August 21, 2014


I am a lover of great restaurants. It’s tremendously difficult to serve high-quality food to hordes of picky customers night after night, and whether it’s a simple barbecue joint or a Michelin-rated bistro, I have enormous respect for anyone who can provide consistently satisfying dining experiences -- the same way I feel about manufacturers of audio equipment with similar track records.

After decades of earning stellar reviews and producing products people like to buy, it’s safe to say that the house of Conrad-Johnson Design is as venerable an enterprise as such culinary establishments as Le Cirque or The French Laundry. These are folks who know what they’re doing. The flip side of a stellar reputation is that people naturally come to expect great things from you. What might be decent in a "good" restaurant can seem weak in an iconic eatery. It ain’t fair, but there it is.

Last year, I was lucky enough to find one of the 200 or so Conrad-Johnson Premier 350SA solid-state amplifiers produced in the mid-2000s. The '350SA is still widely considered one of the world’s great solid-state stereo amplifiers, and from the first day I hooked it up, I knew it was something special. I was struck by how it managed to sound both effortless and powerful. The Premier 350SA is highly resolving while also delivering an incredibly natural, seamless musical landscape, regardless of musical genre. It would not be an exaggeration to say that, with the introduction of the Premier 350SA, the masters at Conrad-Johnson created a product that embodies both the coveted three-dimensionality of tube amplifiers and the control and speed for which the best solid-state models are known. The bar the '350SA sets is very high indeed.

Exactly why C-J ceased production of the Premier 350SA is unclear, but the reasons most often cited were that the overbuilt behemoth was prohibitively expensive and difficult to produce. The Premier 350SA I bought was in mint condition, with very few hours of use. Prior to this find, I had used a variety of stereo amplifiers in my system, including models from Audio Research, Classé, Musical Concepts, Sanders, and Musical Fidelity. So when the MF-2550 SE arrived, I was naturally eager to hear how it would sound when compared with the mighty Premier 350SA, and to learn what the C-J chefs had cooked up this time. Would it be a worthy second course to the gourmet meal that is the Premier 350SA?

Setting up the MF-2550 SE was a snap, although I have one note of caution: before plugging in the power cord, be sure that the power button is not pushed in -- there’s no warning about this in the manual. When I plugged in my power cord, the MF-2550 SE immediately came on. No harm was done, but I prefer to turn an amp on when I choose, and not before all cords and connections have been double checked.

Because the MF-2550 SE contains a fair number of Teflon capacitors (see sidebar), C-J recommends extensive break-in -- 300 hours, to be exact. Although my sample had already logged some hours of use with a previous reviewer, I noticed that its handling of the upper registers became decidedly more natural and grain-free after two weeks of day-long operation.

The first thing I noticed was how quickly -- and seemingly from out of nowhere -- the MF-2550 SE delivered the first drum beats of "Mack the Knife," from Jimmie Dale Gilmore’s One Endless Night CD [Rounder Select ROUCD 3173]. It reminded me of one evening in a French restaurant many years ago, when a waiter’s lighter appeared under my cigarette, before I could reach for my own -- an unexpected but nice touch. This was one fast amp. Gilmore’s voice also had a decidedly "Jimmie Dale" quality as delivered by the MF-2550 SE -- his Lubbock twang was even more nasal than I remembered it from previous listenings. This time, I was hearing his nose and his throat. The MF-2550 SE’s delivery of microdynamics was stunning, and made me want to dive deeper into my music collection.

As I put on the 24-bit/96kHz HDtracks download of Beck’s latest release, Morning Phase [Capitol B0001983802], I was struck by the rich details in "Morning": in the background are layer upon layer inside of layers of electronic toggling and tweaking and phase shifting that I’d never fully noticed before. The MF-2550 SE’s transparency was a bit like hearing everything deconstructed in a way that enabled me to still appreciate each individual element. It was fascinating. It was interesting. But something was missing, and I struggled to put my finger on it. I found myself getting lost in the luxurious detail of the sound, but not so much in the music as a whole. The MF-2550 SE’s transparency had me paying far more attention to individual leaves on the trees instead of what was going on in the rest of the forest.

Next up in my many listening sessions with the C-J were selections from Citizen Steely Dan, the boxed set of remastered CDs of the group’s albums [MCA MCAD 410981]. The MF-2550 SE brought out some subtle guitar fills I’d never noticed in "Babylon Sisters," but the background singers sounded a bit overemphasized compared to what I remembered from my reference. Donald Fagen’s voice seemed diminished in the mix -- or was I just hearing the recording fully exposed and stripped of coloration? The sax solo in "Deacon Blues" is always strident and harsh, but through the MF-2550 SE I found myself reaching more quickly for the volume control. Truth or overemphasis? I’m not sure anyone who hasn’t heard the master tapes would know for sure.

I invited over a friend whom I consider to be an audio master chef. His ability to put a wide variety of high-end systems together and troubleshoot problems is well known among the audiophiles of our area. Whenever one of us is stumped, someone will usually pipe up with, "Ask Blackmore. He’d know." A music teacher by trade, Blackmore is very analytical, not prone to hyperbole, and always willing to offer the unvarnished truth about what something sounds like. We listened to a wide variety of music, from orchestral works to rock and jazz.

After much brow furrowing, foot tapping, and seat shifting, the first words Blackmore uttered during our initial listening session were, "Wickedly transparent." He also said he heard a slight stridency in what he believed was the "5 to 8kHz range."

We agreed that the MF-2550 SE’s presentation of voices was stellar. And because its delivery of microdynamics was so impressive, we were able to hear the full emotional impact of a singer’s intuitive vocal inflections. The MF-2550 SE made it easier to hear a vocalist’s softening of tone or lilt of phrase, which drew us even deeper into the meanings of many lyrics. Whether it was Chet Baker, Mark Knopfler, Alison Krauss, or a classical choral group, the singers sounded as if they were right in front of us -- we could feel the full force of their performances. The dominant adjectives we kept reaching for to describe the MF2550SE’s sonic personality were dynamic, lively, and transparent. As he left, Blackmore turned and said, "I really like this amp."

Two weeks after our first session with the MF-2550 SE, Blackmore asked for another taste. Afterward, he concurred that much of the "edge" we’d heard in our initial session was gone and that the amplifier was hitting all of its marks: It was fast, detailed, transparent, and musical. The soundstage was very stable and focused. Bass notes were tight and textures could be easily identified. The tonal differences between, for example, a Fender electric and a double bass were clearly highlighted. The warmth of the upright’s wooden tones contrasted clearly with the sound produced by the electronic treble settings on the e-bass and its amp.

These are the sorts of details the MF-2550 SE served up best. The 300-hour Teflon Rubicon had at last been crossed.

Among the amplifiers I’ve heard in my system, the Conrad-Johnson MF-2550 SE stands out. Of those amps, its closest competitor in terms of price, specifications, and power is the Classé CA-2300. At $7000, this Canadian anvil delivers 600W into 4 ohms, and was quite capable of handling my Thiel CS3.7s -- and having spent many years with these speakers, I can tell you that, much like their predecessors, the CS7.2s, they will use every watt they can get. The MF-2550 SE produces "just" 400Wpc (confirmed by C-J’s Lew Johnson), but not all watts are created equal. The CA-2300 was a bit sluggish by comparison. The MF-2550 SE gripped the ’3.7s, handling every curve the music threw with agility and speed, and sounding significantly more transparent and musical (in all of the best ways) than the Classé.

While we’re on the subject of watts: The time I spent with the Sanders Magtech stereo amplifier ($5000) a few months ago provided an even greater reminder that numbers don’t tell the whole story. The Magtech pumps out nearly 1000Wpc into 4 ohms, yet I have never heard a quieter amplifier. However, when paired with the Thiels, the Magtech lacked the Conrad-Johnson’s excitement and the Classé’s subtlety. To my ears, the Magtech failed to provide the MF-2550 SE’s "jump factor" and sounded somewhat sterile by comparison.

The MF-2550 SE was addictively resolving, and quicker than any current-model amplifier I’ve heard in my listening room. But how did it stack up against C-J’s own legendary Premier 350SA? By the end of that second session with Blackmore, I was a bit worried about hooking the older model up -- we agreed that C-J’s latest effort would be a tough act to follow.

But while the Premier 350SA ($10,000 when discontinued a few years ago) had lain dormant for more than a month, the differences in character were immediately audible. The first thing I’d been missing since the MF-2550 SE’s arrival can be described in one word: weight. Through the '350SA, drums and bass were heavy and dramatic again. While it failed to fully convey the subtlest textures the way the MF-2550 SE did, the '350SA’s lower midrange was warmer, and its presentation of bass was substantially fuller and more involving. The kick drum on "Mack the Knife" hit my chest very much as the sound of a drum that size actually would if played in my living room. Whether this was a function of the Premier 350SA’s extra 200Wpc or some other design decision, I can’t say. Because the Thiels are pigs for power, it could be that the MF-2550 SE’s 400Wpc might demonstrate more authority with easier-to-drive speakers.

The other major difference between the MF-2550 SE and the Premier 350SA was how the two amps presented the soundstage. Through the MF-2550 SE, performers were more focused between my speakers. By contrast, Blackmore noted that the Premier 350SA "reaches around to hug you." The '350SA’s style is more immersive, enveloping, and cinematic -- instruments fall well beyond the edges of my room and are significantly bigger than through the MF-2550 SE. I’m not talking about a 15-foot Donald Fagen, but through the Premier 350SA it sounds more as if Steely Dan is up on a stage, as opposed to directly across from me. It’s possible that the MF-2550 SE’s soundstage is actually more realistic, but I find the Premier 350SA’s more entertaining.

Listening to the MF-2550 SE during the first two weeks after its arrival was a bit like visiting a stellar restaurateur’s new venue. At first, there were some kinks -- some dishes seemed a bit "too much," and I wasn’t sure whether everything had the proper balance. But by week three, the review unit was in good form, and all the important elements had begun to come together. Now, everything the MF-2550 SE served up arrived with perfect timing. I lingered over it all, savoring every nuance and twist. The MF-2550 SE kept surprising me with new detail, and I will miss it. Nonetheless, I still prefer the Premier 350SA for its immersive, three-dimensional soundstage, effortless power, and warmer tone.

Conrad-Johnson’s MF-2550 SE is an outstanding solid-state amplifier. The Windex-clear window it offers into each piece of music, as well as its ability to deliver lightning-quick transients, are traits that I wish the Premier 350SA possessed in equal measure. Conrad-Johnson is a marquee brand for a reason, and its many accolades are no accident. Perhaps one day the audio chefs of Fairfax, Virginia, will find a way to combine the strengths of their two best solid-state creations into one ultimate masterpiece. Until then, the MF-2550 SE offers remarkable performance and is yet another delight on the company’s already impressive menu.

Price: $7800.
Warranty: Five years parts and labor.

Conrad-Johnson Design, Inc.
2800K Dorr Ave.
Fairfax, VA 22031
(703) 698-8581

Notes on SE and break-in

Conrad-Johnson has long been an advocate of audio minimalism, adhering more closely than most to the "less is more" mantra so popular in hi-fi circles. That translates into a concerted effort to use simpler circuits with less feedback and lower component counts. Look at a C-J circuit and it looks pretty threadbare -- especially compared to the heavily populated, fully complementary boards so popular in so much of the solid-state competition.

But there’s a hidden advantage to C-J’s "traditional" construction technology -- which brings us to that "SE" suffix. Take a look at the company’s product line and you’ll see that, for example, the TEA 2 phono stage is available in three distinct versions: the TEA 2, TEA 2 SE and TEA 2 MAX. Outwardly identical they might be, but internally they’re distinctly different, and their asking prices are distinctly different too. What C-J are doing here is broadly analogous to what car companies do: building a range of models on a single platform. But where car manufacturers offer bigger engines coupled to upgraded suspensions and lower-profile tires, C-J work on the quality of the internal components, substituting higher-grade caps and resistors in an otherwise identical circuit -- to pretty remarkable effect.

In the case of the TEA 2 SE, this adds 50% to the purchase price of the standard model, while the MAX more than doubles it, yet in each case the sonic and, more importantly, the musical upgrades are way more than justified. The TEA 2 is an excellent phono stage in its own right, but the SE makes it sound positively lackluster, while the MAX punches well above its weight, challenging the performance of units that command a significantly higher price (and profile).

Back then to the MF-2550 and that SE designation: Yes, there is a standard version of the MF-2550 ($5200), but it is confined to the US market, mainly because, rather like the TEA 2, once you hear the SE, it makes little or no sense unless you can keep the price at rock-bottom levels -- meaning that there’s no room for an export margin. Even so, after living with the TEA 2 series, I’m not at all convinced that I’d be willing to forego the benefits of SE-level componentry, no matter the saving. The differences are anything but cosmetic. In fact, they’re pretty fundamental to the product’s musical performance and authority.

In the case of the MF-2550, elevation to SE status involves the substitution of 16 polypropylene caps with C-J’s own higher-spec CJD Teflons and around two-dozen critical resistors with precision metal-foil types. That might not seem like much until you take a squint at the circuit board. All those big white cylinders are the Teflons. Not just bulky, they are horrendously expensive, but they reduce dielectric absorption dramatically, even over the polypropylene parts used in critical applications by most other manufacturers. Teflon caps are virtually unheard of in products at this price; this many Teflons in one box -- that’s seriously unusual, not least because of the sheer space they take up. Bringing us right back to the simplicity of C-J’s circuits, the space that allows and the benefits of forward planning that accrue once you realize that a single PCB will have to accommodate more than one set of components -- especially components this bulky -- are significant.

Look at the circuit in a little more detail and the interesting facts start to emerge. Although this is a solid-state design, it is also a hybrid in the sense that it uses a fully regulated FET front-end paired with a bipolar output stage. The FETs were selected for their superior voltage-gain characteristics, behavior that mimics tubes. Fed from its own discrete transformer windings, the MF-2550 SE’s voltage-gain stage is both robust and immune to the large current swings seen in the output stage and their impact on the amp’s power supply, delivering the sort of presence and dynamic range that make tube amps so entertainingly addictive.

The bipolar output stage is configured for maximum current delivery, allowing the amplifier to respond both to the dynamic demands of the signal (preserving the benefits of the FET front-end) and the complex load imposed by the speaker. The large electrolytic caps in the reservoir power supply are bypassed with smaller, faster polypropylene film caps, which also banish electrolytics from the signal path. Local storage capacitance is located directly adjacent to the output devices and hardwired with high-grade cable to further reduce power-supply response time and source impedance. Look carefully and you’ll see that even the cables running to the output terminals are separate and arranged for directionality.

One caution: this is one product you shouldn’t rush to judge. The lucid clarity and natural, uncluttered tonality that typify the use of Teflon caps takes time to appear. Just like Teflon-insulated cables that take forever to run in, in this case "forever" is around 500 hours (or three weeks continuous use), after which it will blossom to such an extent as to be considered a different product. The lean, bleached presentation on arrival, all resolution and flat, detailed perspective but lacking energy and purpose, could easily have been put down to the unit’s solid-state DNA. But once it hit its stride that stark transparency and clarity become fleshed out, both in terms of body and color, without obscuring or cluttering the sense of structure, while adding a sense of shape. If you audition this amp and it sounds cool, detached, uninvolving or in any way distant, then chances are it’s not run in. Give it time and you won’t recognize it.

-Roy Gregory

Associated Equipment

Digital: PS Audio PerfectWave Mk.II DAC, PS Audio PerfectWave transport, Logitech Squeezebox Touch with Bolder Cable Company linear power supply.

Preamplifiers: Convergent Audio Technology SL-1 Renaissance (Black Path Edition), Musical Design Chameleon (Elite Edition).

Power amplifier: Classé Audio CA-2300, Conrad-Johnson Premier 350SA, Sanders Magtech.

Loudspeakers: Thiel CS3.7.

Interconnects: Shunyata Research Zi-Tron Anaconda.

Digital cables: Shunyata Research Zi-Tron Anaconda AES/EBU, Moray James Digital coaxial.

Speaker cables: Shunyata Research Zi-Tron Anaconda.

Power conditioner: Shunyata Research Typhon/Triton stack and Shunyata Research Defender in associated wall outlet.

Power cords: Shunyata Research Alpha Digital, Alpha Analog, Alpha HC, and Venom 3 HC.

Equipment rack and platforms: Vantage Point Contour equipment rack, Salamander amplifier stand, Shunyata Research Dark Field Elevators, Stillpoints Ultra SS speaker risers.

Accessories: Acoustic Revive RD-3 disc demagnetizer, UltraBit Platinum Plus CD solution.