Company Address: 6801 Shingle Creek Pkwy., Minneapolis, Minn. 55430, USA.
The search for the ultimate audio system is a sport which ultimately involves a form of gambling. First, you really have to enjoy the actual search for the best possible equipment and for the best synergy between the components of a complex equipment mix.
Second, you must be willing to take major risks in terms of money. And the whole effort is pointless unless you are willing to risk making a major commitment to your own taste. Anyone can spend a vast amount of money, trusting to the taste of a reviewer or dealer as a substitute for his or her own judgment, but no intelligent audiophile would. Without the excitement and satisfaction of knowing you have personally chosen the equipment you really want to hear and a combination of components that is tailored to your taste, there is no point in buying more than a good mid-fi system.
High-end audio is a sport that goes far beyond the mere enjoyment of music. If music is all you want, it is important to realize that great music can survive virtually any quality of reproduction. The quest for the ultimate audio system is important only for its own sake. You have to be willing to listen to the sound of different cartridges, electronics, and speakers, and make the effort to judge between what are usually relatively minor improvements in sound quality.
Choosing the best components and blending them into a system also means choosing between different approaches to reproducing sound. Every major high-end designer sets different goals and accepts different trade-offs.
No high-end speaker designer I have ever talked to tries to design his equipment to do its best in every room, or to perform at its peak with every kind of music and every type of component.
In the case of electronics, the designers of the world's top equipment --Audio Research, Cello, Classe Audio, conrad-johnson, Counterpoint, Jadis, Krell, Mark Levinson, Jeff Rowland, Spectral, Threshold, et al.--all produce equipment which will work well with other brands, but they design their preamplifiers and amplifiers to work together and to produce a unique balance and combination of trade-offs.
The end result of mixing brands may well suit a given ear, but it almost inevitably involves using a slight coloration in one brand to compensate for a coloration in another. To my ear, the cost is a loss of detail, performance, and excitement.
This may seem like a long introduction to a review of one component. Yet such an introduction is necessary because this particular component challenges the ultimate limits of the high end. The Audio Research M-300 is a mono power amplifier that costs $4,995. No one is going to casually buy this product. Its sole rationale is that there are audiophiles who treat audio as a sport and who want the ultimate.
There is no doubt that the Audio Research M-300 has high-tech glamour. It is the product of one of the top design teams in audio, headed by William Z. Johnson. It is a transistor-tube hybrid amplifier with an all-FET front-end and an all-tube output stage. Its styling has the kind of "form follows function" look that exemplifies current design, and it is physically impressive by any standard. The amp weighs 110 lbs. (50 kg) and is 19 in. W x 10 1/2 in. H x 16 in. D (48.3 cm x 26.7 cm x 40.6 cm). There also are just enough front-panel switches and LEDs to complete the visual image and to provide a useful way of saving tube life without creating warm-up problems.
Unlike previous all-tube Audio Research power amps, the tubes have been removed from the drive stage to eliminate problems with hum, micro phonics, noise, and frequent replacement. The FET drive stages, however, are combined with enough output tubes (eight 6550s) to literally warm the heart of any bottle freak. As for the output circuit, it follows the precedent set by previous Audio Research designs in that it is partially cathode coupled. The M-300, however, keeps the signal voltage of screen grids precisely in phase with the cathode voltage.
Audio Research feels this circuit combines the advantages of true pentode operation with partial cathode z coupling, and can achieve the sonic advantages of Class-A operation without the disadvantages. It achieves high efficiency versus Class-A designs, and the manufacturer also claims that the circuitry virtually eliminates switching distortion and makes the question of class of operation largely irrelevant. The M-300 also has a special output transformer with fewer turns and lower impedance. This design minimizes d.c. in the transformer core, allowing the M-300 to perform better with complex speaker loads.
Bias adjustment is not critical, and output tubes can be replaced without precise matching. There are two fans to ensure proper cooling with minimum noise, and the fuses are front-panel replaceable. (Like most reviewers, I test for product life and reliability by intentional careless handling and irresponsible negligence. The M-300 proved absolutely reliable in spite of many moves, being left on for days, overload, a speaker with an internal short, and all the other quirks that so endear reviewers to manufacturers.) The M-300 is rated at 300 watts per channel into 4 and 8 ohms, with a bandpass of 10 Hz to 60 kHz. Its "clipping" power is 330 watts, and it can drive an unusual range of loads for a tube output stage: There are 1-, 2-, 4-, and 8-ohm taps. Input sensitivity is 900 mV, and input impedance is 60 kilohms. These technical specifications are excellent for a unit using tube output stages, although by transistor standards, they are not as impressive. Total harmonic distortion is rated at less than 0.8%, and typically as below 0.005% at 1 watt. The claimed slew rate is 25 volts per microsecond, hum and noise are below 90 dB, and the nominal damping factor is 30. Make no mistake, however: If all Audio Research wanted was lots of power with good specs, it could have copied some two-decade-old transistor amplifier design. The M-300 is a product for people who can hear, and it is clearly optimized for one type of listener: The audiophile who is seeking the ultimate in musical transparency, detail, and dynamics.
I don't want to overhype this product. The real-world sonic differences between the M-300 and many good high-end amplifiers are relatively limited, and they are only going to be fully apparent with the best possible front ends, sources, and speakers. Nevertheless, this amplifier is probably the state of the art if you are seeking to extract every possible bit of information in the audio range, from the upper bass to the upper treble.
This amp's overall sound quality is difficult to describe to anyone who has never directly compared good with great audio electronics. In brief, however, the M-300 can provide a level of detail, with virtually every kind of music, that is missing in lesser designs. It constantly makes you pause to hear information you did not hear before.
This is most apparent with percussion, but you can hear more sonic detail or every instrument from cello to brass. It also allows you to hear this added detail with every kind of music, from instrumental solos to the most complex passages in grand opera. This makes it remarkably easy to lose yourself it the performance, and to ignore the fact that you are listening to a recording There is no artificial drama in the M300, but there is always that added nuance which involves you more deeply in the performance.
I never have been able to relate the apparent audible speed of an amplifier to measured speed in electronic terms.
Specifications of the M-300 do not show it to be particularly fast, but it sounds exceptionally dynamic when music should sound dynamic. Further, the M-300 does so without making every passage or instrument sound dynamic, as some other designs tend to do. This amp is particularly impressive with ribbon, electrostatic, and EMIM/ EMIT speakers because it brings out their natural coherence and speed; it is a natural way to show just how good the best cone and dome tweeters really are. At the same time, the M-300 is merciless in revealing how much music is lost by most speaker designs, particularly those which lack coherence or which roll off the upper midrange and highs in ways that cost music much of its apparent speed.
The midrange is consistently excellent, although it comes close to being analytic. There is none of the warmth or softening of the highs typical of most tube amplifiers. The M-300 sounds very different from older Audio Research amplifiers or any conrad-johnson or Jadis designs I have heard. It provides more upper midrange and treble detail than any Counterpoint or output transformerless design I've heard. There is almost too much upper midrange and treble information when playing many recordings, particularly the newer digital ones. In a lesser amplifier, this tonal balance would be slightly hard because the amp could not resolve enough inner detail to communicate the full musical character of the recording. With really good and naturally balanced recordings, however, few units can come close to the M-300 in providing so realistic an illusion of sitting close to a live performance and hearing all the information you would hear if you actually were there.
This amplifier is more for music lovers than for lovers of audiophile or trick recordings. It makes ordinary music come alive and restores the glory of many classic recordings, and it does so with effortless conviction. The M300 never seems to strain in handling the midrange of musical dynamics and detail. Recordings you may have criticized in the past will emerge as being better than you previously imagined.
The bass is also very good, even with complex loads like the larger Infinity speakers and the Apogee Duettas.
Driving the few speakers with extended, powerful deep bass, this amp fares better than any tube output stage I have heard. In fact, in the deep bass, it outperforms most transistor amplifiers, including many top high-end designs.
Nevertheless, the M-300 is just slightly lacking in bass control and extension, and even with the shortest possible speaker wires, the bass never quite has the full power and excitement of the top competing designs. Further, a number of other high-end transistor designs do a more convincing job of dealing with instruments such as the cello, bass viol, and bass guitar. This amp is at its best with speakers that do not quite extend down to the lowest bass, and in applications where a little extra power adds bass extension and emphasis.
The practical problem, for most audiophiles, is not going to be judging whether or not the M-300 is a superb amplifier. It is! Rather, it will be judging whether this is the superb amplifier for their system and, if so, getting the best sound this unit can deliver. In most cases, this will mean visiting a dealer who can really show the product off, and then doing some extensive listening and having a long discussion on how to blend the unit into the system.
As with all top high-end products, the problem of achieving synergy with other components is likely to be at least as important as the M-300's inherent sound quality. This amp is not particularly forgiving. As already mentioned, it is wasted on a speaker that is not exceptionally well integrated and that is unable to reproduce every nuance of the upper midrange and treble. You may wish to consult The Best of Audio
'88 for my prejudices regarding the world's best speakers, but I strongly suggest that you listen very carefully to how the M-300 interfaces with the particular speaker with which you intend to use it.
No amplifier is a universal match for all speakers, and the best high-end speakers seem particularly prone to interact in different ways with different power amplifiers. Further, I have found, at my own expense, that the prominence of this interaction can vary from one listening room to another, since so much bass performance is room dependent--as is the proportion of reflected sound at all frequencies heard at the listening position.
The M-300 also does not perform at its best with preamps that do not match its emphasis on apparent speed and transparency. This includes many preamps from competing manufacturers. With the exception of the latest top-of-the-line Krell and Spectral preamps, I found that my efforts to blend the M-300 with transistor preamps tended to combine two different sets of sound characteristics in a way that resulted in a slight, but still significant, amount of information loss.
I got excellent results with Audio Research preamplifiers, however, using the settings that put the absolute minimum of controls and active gain stages in the signal path. This was particularly apparent with their SP11, which has a great many options to' eliminating controls and gain stages, although it was a bit annoying to find that the combination sounded best with the balance control switched out of the circuit.
The best performance of all came when I fed CD players directly into the M-300, set loudness and balance with the amp gain controls, and used either the Adcom SLC-505 or The Mod Squad Line Drive passive "preamps" with short ultralow-capacitance interconnects. I did have gain problems in using some CD players with these passive preamps, and I obviously could not use a turntable. Nevertheless, under ideal conditions, a relatively inexpensive passive preamp like the Ad corn SLC-505 provided a purer and more coherent signal, with less upper midrange emphasis, than the SP11.
This is a considerable compliment to the M-300 since few amplifiers could reveal coloration in one of the world's best active preamplifiers.
These compatibility and interface problems also affect the M-300's soundstage, and some aspects of this are constants. The M-300 always has excellent imaging, a slightly forward apparent listening position, and very good though not outstanding depth.
Like many mono amplifiers, this one reveals a very wide soundstage, although it is one that tends to produce a "hole in the middle" effect in some stereo recordings. I found that I had to move most of the speakers I tried slightly closer together than usual to get the proper central focus.
One simple punch line emerges from all of the above complexities: The Audio Research M-300 is a superb power amplifier! I hope, however, that this review will also convert a few heathens to the sport of "high end." I realize that the foregoing description of my efforts to obtain a personal best out of the M-300 may seem as dull to some readers as listening to a camera buff discuss lenses. For a precious few, however, it will be their introduction to a game that can be almost as enjoyable as listening to music.
--Anthony H. Cordesman
(Editor's Note: At press time, Audio Research told us that the M-300 has been replaced by the M-300 Mk. II, for $5,495. This will have a five-position attenuator switch in place of the tested unit's input level control, a new capacitor network in the output stage, and a different front panel and top cover.)
[adapted from AUDIO magazine/Nov. 1988]
Also see: Audio Research D-250MKIIS Amplifier (Dec. 1986)
Audio Research SP-10 Preamp and D-70 Amp (June 1984)
[adapted from Audio magazine]