Convergent Audio Technology SL-1 preamplifier Jack English 1992 part 3
The frequency balance through the critical midrange frequencies was neutral and flat, but that was just the tip of the iceberg. This was much more than simply a neutral tonal balance. One of the CAT's wonderful strengths was its ability to correctly re-create the mix of fundamentals and harmonics leading to identifiable timbral signatures. An excellent illustration was the constantly repeated melody of Ravel's Bolero (Herbert von Karajan, Berlin Philharmonic, Mobile Fidelity MFSL 1-513). As each different instrument took up the melody in turn, its subtle tonal distinctions were rich, natural, and uniquely distinct.
Another good illustration was Andreas Vollenweider's Book of Roses (Columbia CK 48601). This recording uses a wide array of instruments ranging from the familiar to the exotic. Cellos sounded like cellos, cymbals sounded like cymbals, and harmonicas sounded like harmonicas—as did every other instrument I was familiar with. Since the things I knew sounded as they should, I assumed that I was hearing what an erhu or charango really sound like. The overall timbral tapestry of different instruments was a welcome change of pace from Vollenweider's ever-present electric harp.
The Signature's tonal rightness consistently conveyed the proper mix of fundamentals and overtones, but must have done it in part by maintaining everything in proper time and phase perspectives. In comparison with any number of other preamps, I was consistently taken with the lack of texture or grain, the total lack of mechanical feeling added to the music, and the overall sense of refinement, ease, and subtlety. Once again, I can only assume that the CAT minimized unwanted, amusical, odd-order harmonics. In terms of midrange splendor, the Signature represented the best of what tubes are all about. (Are you listening, Dick Olsher?)
The CAT is not alone among tube preamps in providing a glorious midrange. Other, far less capable units have done as well in this one area. What truly set the Signature apart was how well it did so many other things without sacrificing any of that glorious midrange. Where many other tube preamps fall short is in the re-creation of sounds at both frequency extremes—the uppermost trebles and the deepest bass. Early on, the CAT preamps were able to produce wonderful trebles; the Signature has taken still another step in the realistic re-creation of the uppermost frequencies. I was most aware of this from the pervasive, obtrusive levels of tape hiss on such CDs of older analog material as Saint-Saëns's Symphony 3 with organist Marcel Dupré (Mercury 423 719-2), or the Italian progressive rock group Museo Rosembach's Zarathustra (Contempo Records 004). More important, the upper harmonics of stringed instruments were often glorious (eg, Rimsky-Korsakov's Scheherazade, Chesky RC-4), as were the percussive attacks and decays of triangles and cymbals. The outstanding treble performance was equally outstanding through either the phono or line stages.
With each revision, CAT preamps have improved in the bass, a notoriously difficult feat for tubed products. The Signature was the best of the series, particularly impressive in the mid- and upper bass, where it had power, clarity, and surprising speed. Individual bass notes had pitch and definition, attack and decay, dynamics and authority. There was no noticeable change in sonic character from the midrange through the midbass. Since the vast majority of bass information is in this region, there was simply nothing negative to report. This tubed preamp was very much at home with such hard-rockin' material as Richard & Linda Thompson's classic Shoot Out the Lights (Hannibal HNCD 1303). There was drive, pace, and a fine sense of rhythmic integrity. Another wonderful illustration of the Signature's bass prowess was Dead Can Dance's "Saltarello" from A Passage in Time (Rykodisc RCD-20215). This track contains some awesome percussive midbass information which the CAT handled with aplomb.
Large orchestral works were equally impressive, with wondrous midbass foundations. The splendid Athena reissue of Rachmaninoff's Symphonic Dances (ALSW 1001) made it abundantly clear why I had placed this LP on my 1992 "Records to Die For" list, as well as reminding me just how superlative vinyl can be. The CAT's phono stage was simply stunning with great recordings like this one. In the area of mid- through upper bass, the Signature took a back seat to no other preamp I have heard.
Only in the very deepest bass did the CAT fail to equal the performance of some other great preamps. With most speakers, the preamp's limitations won't even be noticeable. In my case, it took the monstrous Kinergetics SW-800 Subwoofer System to uncover this minor weakness in the bottommost frequencies. The Saint-Saëns organ symphony lacked just a tad of its wonderful deep-bass foundation, as did the meandering bass line in Go-Corey-Go Greenberg's "Eden," from the second Stereophile Test CD. On this latter track, the bass actually lost significant impact as the CAT attempted to reach into the depths of the frequency spectrum.
Its tonal splendor alone would make the Signature one of the world's great preamps. From the midbass through the highest trebles, it was simply captivating. But the astounding strengths hardly stopped there. Measurements (eg, power ratings) notwithstanding, the vast majority of high-fidelity equipment severely restricts dynamic range. Yes, most stuff can play loudly, but not all can. We can quickly recognize ultimate volume limitations. Try some Nirvana or Led Zeppelin on a pair of old Quads if you want to hear real-world volume constraints. It's also true that many pieces of equipment don't sound natural at low levels. They have to be pumped up to a certain level to come alive. In either of these cases, it's clear that the ultimate dynamic range of live music can not be reproduced—too soft, and there's no life; too loud, and all sorts of catastrophes can happen.