Integrated Amp Reviews

First, with the GoldenEar Triton Twos in the system, I turned on the ProLogue Premium, waited five minutes, and played track 3 of the Chesky Records Jazz Sampler & Audiophile Test Compact Disc, Vol.1 (Chesky JD37). I listened carefully, noting all the little sonic details, stopped the CD, and left the room for an hour. I then went back to the listening room—where the system had been on all this time, but without playing music—and listened to the same track again. (The volume control was not touched.) My conclusion—which those who want double-blind controls are free to ignore—was that there was indeed an improvement, and of the sort that I'd previously noted more informally. What I thought was interesting was that the improvement did not depend on the speakers playing during the warm-up period. It's possible that playing the speakers would result in a further improvement in the sound, but it would require some additional comparisons to determine if this is the case.

Sound: Take One
I used the ProLogue Premium with three speakers: my reference Avantgarde Acoustic Uno Nanos (reviewed in July 2009), the GoldenEar Triton Twos (February 2012), and, briefly, the MartinLogan Montises (soon to be reviewed). These speakers represent a wide range of design approaches, and sound quite different from each other.

First up were the Avantgardes. With these speakers, I always experience a degree of trepidation when I turn on the system after installing a new amplifier. Never mind any subtleties of sound quality—is there noise (hum or buzz) at a level that's likely to interfere with my enjoyment of the music? Whatever noise there is at the output of the amplifier, the Avantgardes, with their +100dB sensitivity, will let me hear it. I can try to "listen past the noise," but I don't like having to do so. With the last amplifier I reviewed, the otherwise admirable Conrad-Johnson LP125M (December 2011), I had to go to all kinds of trouble—grounding/ungrounding different parts of the system and dressing the interconnects—before the noise abated to the point where it was negligible.

Turning on the system with the ProLogue-Avantgarde combination for the first time, I was much relieved to find it dead quiet. With the volume turned way up but no music playing, no sound came from the speakers; it was as if the system were not on at all. Very impressive—and it boded well for the time I was about to spend with the ProLogue. The Avantgardes are known to present a high-impedance load, so I connected them to the Premium's 8 ohm taps; a brief comparison using the 4 ohm taps showed only a marginal difference, one in favor of the 8 ohm connection.

The preamp and power amp that I've found to work most optimally with the Avantgarde Uno Nanos are Convergent Audio Technology's SL-1 Renaissance and Audiopax's Model 88 Mk.II. The 30Wpc of the Audiopax is more than enough to run the Avantgardes to high levels, and the combination provides a near-ideal mix of timbral accuracy, detail, and dynamics. Changing from the CAT-Audiopax to the ProLogue Premium might be expected to have produced a sense of disappointment, but my feeling was one of excitement: this integrated amp, costing a mere fraction of the CAT-Audiopax combo ($32,000 with the latter in its current, Mk.III form), was able to produce sound that was faithful to the source, musically involving, and altogether very listenable. Like other tube preamplifiers and amplifiers that I have experience with, the ProLogue Premium had a special way with voices, reproducing them in a way that had a more "human" quality than with even topnotch solid-state products like the Simaudio Moon Evolution W-7 power amplifier.

Listening more critically, comparing the ProLogue Premium with the CAT-Audiopax at matched levels, I heard some differences. With the CAT-Audiopax, the sound was more convincingly three-dimensional, with more "air" around voices and instruments; the highs were more detailed without becoming overly bright; and it was easier to follow the music's subtle ebb and flow. These differences—apparent when I was wearing my "sharpener" hat—are to be expected, given the price difference. People who have $18,000 to spend on speakers like the Avantgarde Uno Nanos can usually afford to spend more than $2299 on an integrated amp, and probably should, to get the most from their speakers. However, if you've picked up a used pair of Uno Nanos (or Unos or Duos) at a bargain price and don't have a lot of money left over, the ProLogue Premium would give you maybe 90% of what these speakers are capable of—and outside of an A/B comparison, you wouldn't know what you were missing.

Sound: In the Real World
The Avantgarde Uno Nano is a rare bird: ultra-high efficiency, horn-loaded midrange and tweeter, powered subwoofer. Evaluating an amplifier with this speaker, while useful, doesn't tell you how the amp will fare with more conventional speakers—and, of course, there's a major mismatch in price. Keeping these factors in mind, I spent most of my ProLogue Premium reviewing time using speakers that are less exotic in design and provide a better price match: the GoldenEar Triton Twos.

The Triton Two is one of my favorite speakers: a floorstanding three-way that sells for $2999/pair, whose sound quality comfortably exceeds what is normally expected at this price level. Like the Uno Nano, the Triton Two incorporates a powered subwoofer. Its claimed sensitivity, confirmed by John Atkinson's measurements, is 91dB—somewhat higher than the norm, but much lower than the Uno Nano's. JA also noted that "the speaker will not be too difficult for the partnering amplifier to drive."

The combination of the Triton Twos and the ProLogue Premium proved particularly synergistic—it was as if each designer had used the other's speaker to fine-tune the sound of his own. The speakers sounded good through the ProLogue Premium's 8 ohm connectors, and even better—more dynamic, more "present"—through the 4 ohm taps.

Comparing the ProLogue Premium to the Audiopax 88 Mk.II and the Simaudio W-7, each driven by the CAT SL-1 Renaissance preamp, there were areas of performance in which each of these high-end references sounded superior.

The Audiopax's major area of superiority was its ability to present recordings that normally sound a bit harsh in a way that made me think that the recording sounded better than I'd realized. Come Fly With Me (CD, Capitol CDP 7 48469 2) catches Frank Sinatra at his confident best, with Billy May's arrangements and musical direction providing perfect support, but there's no getting around the fact that the massed strings have a certain edge, whether from limitations of the 1957 recording technology or the digital transfer. This edge was less noticeable through the CAT-Audiopax combo than through the ProLogue Premium.

The Moon W-7 had more of this edge than the ProLogue Premium—and much more than the Audiopax—but it beat both tubed amps in its sense of power and dynamics, had more extended bass, and was able to drive the speakers to a higher level without strain. The sonic character of the ProLogue Premium was in between the Audiopax and the Moon W-7. At times, listening to the system with the Audiopax in it, I thought, Yes, this is the way it's supposed to sound—and then I began to get the feeling that the sound was too smooth, too liquid. Similarly, when listening to the system through the Moon W-7, I was impressed with the clarity, definition, and dynamic swing—Yes, this is more like the real thing. Then my critical self again reared its head, and I began to feel that the sound was a bit on the aggressive side, pushing the music toward me rather than drawing me into it. And whenever I switched over to the ProLogue Premium, I had the feeling that here was an amplifier-speaker combination that just "clicked." For an integrated amplifier that costs a mere fraction of these high-end references, this is remarkable performance.

The ProLogue Premium's Home Theater input bypasses the preamp section, including the volume control. I did a trial using this input, connecting it to the output of the CAT preamp, with the Ayre Acoustics CX-7e^MP CD player connected to the CAT preamp's input. In this setup—in which I used the ProLogue Premium as only a power amp—I could evaluate the contribution of the ProLogue's preamp section to the sound.