Krell KRS-2 preamplifier Page 2
I should stress in introducing them that: a) these comparisons always involved a single sample of an active preamp; b) some of the preamps used were borrowed from other audiophiles and were not necessarily typical of the latest production of a given model; and c) many differences were so minor that they would only emerge after prolonged listening. Nevertheless, I was able to make the following differentiations:
Audio Research SP-10: The sound was slightly warmer, with a minor exaggeration of imaging which seems to come from a coloration which "expands" the dynamic contrasts of instruments with a strong separate signal. Upper midrange and treble were slightly sweetened at the expense of detail. Bass was rich and powerful, but there was a definite loss of detail in organ voices; the lower strings had added power at the cost of some loss of information.
Audio Research SP-11: The SP-11 remains one of the best sounding preamps ever built, but it had two minor forms of coloration. The first was in the bass. It lacked the ability to resolve complex organ voices fully or the difference between the organ and the lower register of the cello. The second was a minor presence peak; this gives the SP-11 its unique detail and apparent transparency, but slightly overshadows the natural warmth of the midrange and upper bass. These colorations were reduced as gain stages and features were removed, but never fully disappeared.
Conrad Johnson Premier Three: There was a slight veiling, warmth, and added depth and focus of the soundstage around the center of the stage. Music was sweetened, with a softening of upper octave energy.
Krell PAM-3: Music sounded slightly compressed, with a loss of dynamic contrast. The soundstage was slightly narrowed, with reduced height. There was more apparent depth, but not all the information necessary to make that depth believable was present.
Meitner PA-6: A slight but audible veiling could be detected, and there was a slight loss of dynamic energy, particularly in the lowest-level passages.
Onkyo P-308: This high-end Japanese preamplifier featured a distinct hardening of the upper five octaves, limited veiling, and an etched, two-dimensional quality to the soundstage.
PS Audio 4.5: A slight veiling and hardening was noted with the high-level gain stage switched in. The soundstage was artificially widened, and some noise was introduced at very low listening levels. The Mod Squad Line Drive sounded slightly cleaner than the 4.5 used in passive mode.
Tandberg TCA 3018A: There was a slight apparent emphasis of the upper octaves from about 15002000Hz upward, with a concomitant slight loss of depth and a tendency to etch or exaggerate the main musical signal at the cost of a slight loss of subtle harmonics.
I must repeat that I was comparing some of the best preamplifiers. The results of active vs passive listening tests with many other products ranged from annoying to unpleasant. At the absolute nadir of sound quality, a comparison of the Mod Squad Line Drive with the preamp stages of the Pioneer VS-X5000 receiver showed that the Pioneer veiled the sound to the point where it sounded like it was introducing a series of filters, the designer adding new layers of compensation for each previous mistake.
At the mid-fi level, most units forced me to drag the word "transparency" out of the closet of overworked audio terms. The fact is that most mid-fi units remove enough musical data to blur many of the sonic differences focused on by this magazine.
Even some borrowed high-end units sounded colored enough to make me omit them from the above list, pending confirmation that I was listening to a unit up to the manufacturer's specification. It was all too clear that specmanship and price were no basis to predict the degree of veiling or coloration that would emerge from prolonged listening to a wide range of music, even when careful attention was paid to interconnects, exact level matching, and impedance (footnote 1).
Enter the KRS-2
This brings me to the Krell KRS-2. I would praise its sound under any conditions, but what fascinated me about it was the extent to which it passed the active vs passive preamp test. Whether or not other reviewers get the same results from this test, I suspect that passing the "active vs passive" test will soon be a critical measure of the state of the art in every preamp, and that most designers are soon going to have to refocus their effort in this area. In fact, I will be surprised if there is a single top quality preamp on the market that will not have changed six months from now as more and more designers pay closer attention to the neutrality of the high-gain stages in their units.
Accordingly, I was more than a little impressed by the fact that the only areas where I could catch the sound of the KRS-2 out were a slight narrowing of the soundstage and a resulting tendency to move the apparent listening position a bit to the rear (footnote 2). I have not heard the latest Cellos or Levinsons, but was continuously surprised by the fact that, in test after test on different kinds of music, the Krell proved to be neutral relative to a passive preamp, even when I initially preferred the sound of another unit or thought it would be more neutral.
These judgments about the KRS-2 were echoed by a number of other listeners. I had more than a dozen manufacturer and audio industry visits during the time I was running these comparisons, and I used them to get a broader set of impressions. In each caseand without any suggestion from me and in blind listening tests using a variety of front ends, amplifiers, and speakersother listeners preferred the clarity or transparency of the Krell KRS-2 or Mod Squad Line Drive over the other active preamps I had on hand.
I should hasten to note, however, that other listeners did not necessarily prefer their overall sound. Several felt, for example, that the Audio Research SP-11, for example, had slightly more believable musical dynamics. I would also agree that the SP-11 is characterized by a more forward apparent listening position that often suits the miking distance from the performance better than the Krell.
Other top-ranking preamps had similar areas of merit, and, since the test of a high-end system is not technical accuracy but musical believability, various listeners tended to prefer the overall balance of other preamplifiers because they felt such units offered more overall musical believability.
Nevertheless, virtually all of those subjected to my listening tests agreed that the Krell KRS-2 revealed the core of the music with a freedom from veiling and coloration that no other active preamp quite matched. Even when the KRS-2 initially seemed to lack the detail or dynamics of other preamps, it was interesting to go back into the music and listen again to the details.
I have several solo violin recordings, master tapes of amateur performances, for example, which give a good picture of how complex the sound of a violin can really be. The Krell KRS-2 showedmore than any other preampthat even the best CD players and recordings still do something to the sound of solo string instruments, tending to "simplify" their harmonic structure. While many CDs are now very musical, the KRS-2 showed that they still miss something very important. It helped reveal that CDs still tend to make every violin sound like a modern violin, or one tuned to emphasize loudness and dynamics rather than harmonic richness.
The Krell KRS-2 also extracted more music from the noise floor of the tape than any other preamp. I'm not sure how to put this particular sound characteristic into words, but anyone who listens to chamber music is probably more interested in the reproduction of soft passages and fine detail than in the louder passages. Purity in this aspect of musical sound consists of the ability to "reduce" any interference with the musical richness to the point where even the most subtle changes in the recorded signal do not have to compete with the noise or distortion of electronics. The Krell KRS-2 competes less with the music than any other preamplifier I have yet heard. I also was impressed with the phono stage of the Krell KRS-2. Overall, it was quiet and neutral to a point where no other preamplifier I know of could rival it. The Audio Research SP-11 competes when used with medium- to high-output moving-coils, but the Krell can take any moving-coil and offer almost absolute silence without any problems in terms of dynamics.
This initially may make the Krell seem to lack sonic excitement or "color," but what it really lacks is coloration. Again, the KRS-2 lets an amazing amount of fine musical detail pass through all its gain stages, and does so in proper balance. There is no euphonic coloring, irritating etching, or exaggeration of the soundstage, and no trace of upper-range hardness or softness. A tube lover who wants both the sweetness of tubes and flat, accurate timbre coupled with outstanding performance at the frequency extremes will have no trouble with the phono stages on this unit.
I have nothing more to add about bass, treble, midrange, soundstage, dynamics, and all the rest. The Krell KRS-2 is a unit where you have to struggle to find something to criticize: it is a superb performer in every area. It is one of the three or four preamplifiers that should be auditioned by anyone looking either for the very best or for a professional reference.
If there is anything at all that may present problems for some audiophiles, it is likely to be the KRS-2's lack of the more forward, or "dynamic," sound typical of most top-quality preamps. I have to confess that I am used to a more forward, dynamic sound myself, and find it hard to stop listening to the Audio Research SP-11 for this reason. At the same time, however, I have to state that when I compare the KRS-2 with the sound of a direct CD or tape deck to power amplifier hookup, the sound of the Krell is more representative of what I hear than the forward sound of competing preamps.
In summary, therefore, I feel the Krell KRS-2 to be as seminal a preamplifier design as the Audio Research SP-11the two finest units I have yet heard. Where the SP-11 revealed a new degree of detail, the KRS-2 reveals a new degree of neutrality and transparency. It shows the way toward what I predict will be a major improvement of high-gain stage performance throughout the audio industry.
Footnote 1: Let me caution you strongly against trying this test at a dealer, unless it is a top-quality dealer with measuring instruments and a lot of time and patience. Remember that both the active preamp and any passive preamp you use as a reference will have some sonic colorations, as will any A/B device. Each will interact differently with different signal sources and amplifiers. A passive preamp is not necessarily correct, merely less colored in some areas, and often at the expense of more coloration in others. The levels used must be adequate to drive the power amplifier without gain problems in the passive preamp, and must be matched carefully using the actual musical signal source at some predictable point in the music and at the amplifier output to the speaker. Nominal matching at the power amplifier input using a test-tone like pink or white noise did not prove to compensate for the finer differences in impedance, level, and dynamics, and even using test gear to match levels at the amplifier output was often problematic, given the very different ways in which any two units handle musical dynamics. Careful use of interconnects is critical. Many good high capacitance interconnects or phase-corrected interconnects are not suitable for such tests, and it takes a lot of listening with a wide range of music, and sufficient practical experience, not to be taken in by some wiring error. Even then, the main audible result of an active versus passive test will often be to determine veiling or loss of detailnot overall performance.
Footnote 2: One note of caution. The first Krell KRS-2 I received did not have its specified gain in the high-level stages due to a wiring error in the initial samples. My comments are based on a sample from the first full production run.