August 1999Conrad-Johnson MF2500 Amplifier
by Todd Warnke
Back in dark days of the early 70s, when transistors, like so many Visigoths, were sacking the centers of high fidelity, Bill Conrad and Lew Johnson, then a couple of Federal Reserve economists, joined forces to help keep the music-loving community safe from barbarism. And from their first products, all of which were tubed, the combined Conrad-Johnson Design, Inc. has been about musical flow and not mega-buck looks or glossy ads. Through the 70s and into the 80s, Bill and Lew held the musical high ground with thermionic values. But then, like the Romans of ancient day, they learned to assimilate the good in their old enemies and began to design with transistors.
The Motif line, begun about 1983, was the first of the counterstrike designs, and was well received. Well built and well designed, Motif equipment set the standard for musical solid-state gear. The acquisition of Sonographe, around the same time, led to an entry-level solid-state line. And around 1987, a solid-state CD player became the first non-tube product to carry the C-J name. That player was soon joined by an amp and preamp, which completed the subordination of transistors to the C-J aesthetic. And all of this brings us to the latest of the silicon-state C-J products, the MF2500 amp.
Under the hood
Every reviewer, regardless of technical skill -- and keep in mind the old adage, "those who can, do, and those who cant, review" -- is required to open the case, just so he can say "under the hood" or some such thing in his review. The packed-but-clean and well-dressed circuit board of the MF2500 bears witness to the skill of those who hand assemble each amp. The circuitry inside the case uses both bi-polar and FET transistors. In the voltage gain section the MF2500 uses FETs because, according to C-J, FETs have a distortion characteristic that, like tubes and unlike bi-polars, minimizes odd-order harmonics. On the other hand, the output stage, where low output impedance is of primary importance, bi-polars are used since they have about one-quarter the output impedance of FETs. Conrad-Johnson feels that this combines the better distortion characteristics of FETs and the drive capability (and hence better bass response) of bi-polars. As for numbers, the amp puts out a burly 240 watts into an 8-ohm load.
At 7 1/2" high and 19" wide, the 3/8" thick, champagne faceplate gives the amp a substantial look, and at 16" deep and 56 pounds, the amp is substantial. Besides the C-J logo, a power switch mounted in an oval cutout which is bisected by a vertical groove in the faceplate, and a red LED power indicator, the MF2500s fascia is clean. Around back, the straightforward theme is carried on. A captive power cord and fuse holders are on one side while the other has a pair of Cardas RCA input jacks and a single pair of Cardas five-way binding posts per channel. Since the circuit board is laid out east/west rather than the typical north/south, heat-sink fins are located on only one side of the amp.
Now that weve covered history and specs, we can get to the heart of the issue -- namely, how the MF2500 sounds, and for that Im going to steal a line from Michael Fremer. In the July 99 issue of Stereophile (coincidentally, in a review of a C-J product), Fremer commented that great products have "soul," and that the soul they have comes from the soul of their designer. Well, the MF2500 has a large measure of the soul that Bill and Lew have given all their products. In short, it sounds like a modern C-J design.
Beginning tonally and at the bottom, the MF2500 has superb bass extension with very good definition. A disc I play a lot (for the music thereon, but also to test the bass) is Roy Hargroves Habana [Verve 314 537 563-2]. The opening track, "O My Seh Yeh," uses a bass drum and bass guitar to set the heartbeat that drives the tune. With the C-J MF2500 taking the place of my reference Blue Circle BC6 amp, the bass had better depth and a bit more slam, which gave this track greater presence as well as better definition of the recording location. But it was also just a slight amount less developed and less textured. Considering that my in-house reference for bass tonal development is the BC6, and that the MF2500 had better depth and slam, the C-J acquitted it self quite well.
The mids of MF2500, as you would suppose, were well served. On the Hargrove disc, the guitar parts (courtesy of the under-appreciated Russell Malone), add tonal depth and richness to the session. As with any recorded guitar, too much emphasis on the snap of the strings, and the tonal richness is lost, while too much emphasis on the middle of the note, and the recording loses pace and clarity, a factor of special import in this New York-cum-Havana session. The story here is that the C-J gets this balance just right, which makes all music, not just this disc, a very natural-sounding and moving event.
Treble, out of the C-J mold, is well rendered, if stopping just the slightest bit short of the absolute top. The good news here is that this both avoids the typical solid-state nasties while having a near insignificant effect on detail retrieval. Jimmy Cobbs brush work on Kind of Blue, in either vinyl or polycarb form [Classic Records CS-8153 and Columbia CK 64935], is absolutely essential to the feel of the session. With the MF2500 in the system, Cobbs sense of floating beyond both time and emotion while offering comments on each is of the first rank. Still, on other recordings, such as Takemitsus From Me Flows What You Call Time [BBC Music Vol. II, No. 11], specifically where the bells and percussion cut through the orchestra, the tone of the highest frequencies was accentuated and just the slightest bit of the high overtones were down in level.
Dynamic contrasts, on both the micro and macro level, were very well rendered. On the new DCC reissue of Nat "King" Coles The Greatest Hits [DCC GZS-1127], "Orange Colored Sky" opens with soft piano, bass and voice orchestration. About 15 seconds in, the background singers and brass open up, and Ella, the Rat Dog, nearly jumps out of her skin. Using the C-J, this sudden jump was, as far as I can tell, 100% accurate -- no compression, no shrinking of the stage, no smearing or squashing, just a big bang worthy of universe creation. As for the micro level, the sense of breath you hear, whether on a Margo Timmins vocal, a Hank Mobley sax solo, or a quiet Debussy piano passage, was not quite up to the same level of the Blue Circle BC6, but certainly in the same general class.
For me, the defining characteristic of the MF2500 was its ability to create a stage, another traditional C-J strength. While Im not an imaging freak -- I can and do enjoy music in mono, on headphones, in the car and from a boombox -- I also enjoy the illusion of music being made by real people in real space, and this amp has the magic skill of creating images like nothing Ive heard before. In fact, the MF2500 does spatial tricks that I thought were only the province of speakers. Its not just a right-to-left thing alone, although this attribute is remarkable as images project at least three feet beyond the speakers. Nor is it the depth, which is almost as incredible. Nor is it even the way width and depth combine to give the smoothest, deepest and best-defined soundstage Ive heard in my house, a soundstage that remains stable in the back corners and even under heavy loads. But it is also the way the speakers completely disappear as identifiable sound sources and become nothing more than tall furniture. Does this increase the musical experience? Well, it sure helps cement the illusion of a real space, and that does increase the musical reality, at least for me.
Clarity, a small stumbling block of C-J solid state amps in the past, was improved as compared to my recollections of past models. However, the MF2500, while very good, is still is not quite in the absolute first rank in this area. The stage it threw was world class, as I said, the best Ive heard, with corners that remain stable regardless of load. But images in those deep corners lacked a bit of texture as compared to the best amps I had through here. To clarify at bit, Im not calling the MF2500 muddy; it isnt. Nor is it grainy, gray, golden-toned or cloudy. But the sense of openness, of having an unobstructed view of the back row that class-A solid-state or OTL amps offer is missing. Of course, to get this means putting up with class-A or OTL issues, and this C-J is about as issue-free an amp as I know. Seemingly, the MF2500 has no current issues, no heat issues, no compatibility issues. Just hook er up and let er rip.
Compare and conclude
After several months of listening to the MF2500, I brought out my Blue Circle BC6, a 25Wpc, single-ended, class-A, solid-stater for a more complete comparison. Putting the Blue Circle amp in helped to highlight the advantages of the MF2500s 240 watts. While not a dynamic weakling, placed up against the MF2500, the BC6 was just not able to create the WHOMP that the C-J could. It also re-created a smaller soundstage than that of the MF2500. On the other hand, the BC6 accentuated the emotional subtext of music in a more involving and, in some ways, a more accurate manner than the MF2500. Also, while the stage was smaller, each player had a greater density with a fuller harmonic structure to their presence that more closely mimics reality. And, in spite of the denser harmonic presentation of the BC6, it also offers that unobstructed view I was just referring to.
But comparisons only go so far. Taken on its own, the Conrad-Johnson MF2500 is wonderful amp. It has tremendous power reserves, which it uses to superb musical effect. Dynamic contracts are fully and properly scaled. Staging is not only otherworldly, it maintains that dramatic spread and depth even when pushed to neighbor-annoyance levels. And, out of the classic C-J mold, it offers a grainless, smooth but not overly rounded view. It does slightly lean out harmonics, more so in the lower registers than in the all-important mids, but the shift is small enough that system matching can easily compensate. For example, with the Totem Arro, a slightly rich-sounding speaker, the harmonics took on a more even-handed balance.
But even taking these minor characteristics into account, the new Connie-J amp is a formidable product. The MF2500 gets a recommendation, especially for systems where loads of power are needed.
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