Convergent Audio Technology SL-1 preamplifier Robert Deutsch 1999
Ken Stevens is pretty hard on reviewers. Oh, he's a pleasant enough fellow, even congenial. Unfortunately, he has a bad habit: Every couple of years he comes out with an improved version of the Convergent Audio Technology (CAT) SL-1 preamplifier. This results in scads of reviewer praise, which then leaves us scrambling to find new superlatives when he comes out with the next latest-and-greatest version.
After the original Stereophile review of the SL-1 Signature by Jack English (Vol.15 No.12), it fell on me to do the Follow-Ups on the Mk.II (Vol.19 No.12) and, most recently, the Mk.III (Vol.21 No.3). The SL-1 Signature was already an excellent preamplifier—if not, it would not have been awarded Product of the Year in 1993—but each new version has been better still.
The SL-1 Ultimate (price remains $5950 including phono stage, $5350 for the SL-1L line-stage-only model) differs from the Mk.III in the following ways:
• more capacitors, of higher value, added to the main circuit board;
• all capacitors are now custom-made for CAT, and generate less internal vibration than those previously used;
• more RC filters for better power-line-filter noise regulation;
• decoupled cascaded regulation across the entire audio band, using MOSFETs as regulators;
• associated components (resistors, Zener diodes) increase the parts count by 30 to 40 (Stevens couldn't tell me the exact number);
• new proprietary wire used in internal wiring (same gauge as before, but higher-quality copper and better dielectric); and
• new circuit board, designed to accommodate the additional capacitors and other components.
According to Ken Stevens, the idea for the changes that led to the SL-1 Ultimate came from his work on CAT's huge JL-1 monoblock amplifiers. In refining the JL-1 design, he came up with a scheme for using power-supply capacitance that resulted in significantly improved sound, and he thought he could improve the sound of the SL-1 by applying the same technique. What made him hesitate at first was that he'd have to change the circuit board, which meant that previous versions of the preamp would not be upgradeable to the Ultimate—a move that would not endear him to his loyal customers. However, once he'd built and heard the Ultimate prototype, he knew that it had to be produced.
Nice Kitty: When I settled on the first CAT SL-1 Signature as my reference preamp, I did so because it seemed to offer the "musical" sound typical of tube preamps, but with fewer colorations and with noticeably higher resolution. Since then, I've had a chance to evaluate at length several other high-end preamps, both tube and solid-state, and although there are some that I could live with easily—and there are definitely ones whose ergonomics I prefer (I'd like remote control and a finer gradation of volume)—I haven't heard one whose sonic performance I felt was, overall, superior to the CAT's. And, with every revision, the preamp changed in ways that brought me closer to the music, imposing less of its own personality—clear evidence that the designer knows what he's doing. The Ultimate advances this process to an even higher level.
Manufacturer's hyperbole notwithstanding ("a HUGE reduction in grain and mechanical sound...ALL other preamps sound coarse and mechanical by comparison," etc.), the improvement that the Ultimate represents over the Signature Mk.III is not such that you wonder how you could have tolerated listening to that old piece of junk. At the same time, it's definitely not trivial. In fact, I think Ken Stevens has managed the trick that all the best high-end designers strive to pull off in their products: to provide you with greater musical detail without giving you more of the electronic artifacts—or, alternatively, to reduce the electronic artifacts while preserving the musical detail.
The Ultimate sounds even more detailed and highly resolving than its predecessor, and there's a reduction—I'm tempted to say an "elimination"—of the "electronic" overlay (grain or haze) that was previously present to a degree that I'd thought was negligible. The entire range, but particularly the upper midrange and treble, has a pristine clarity without in any way sounding etched or clinical. The term "listening fatigue" is not one I would associate with the CAT in any of its incarnations, but the Ultimate sounds more relaxed, more liquid, and draws me more into the music. There is also an improvement in dynamics, the music seeming to "breathe" with greater freedom. All of the CAT's other virtues are still there in full force: an enormous soundstage with pinpoint imaging (speakers permitting), extended and tonally neutral bass (this is not a traditional warm-sounding preamp), very low noise level (approaching that of the best solid-state preamps), and timbral accuracy.
If you're a CAT owner, the introduction of the Ultimate places you in a quandary. Given that previous versions of the SL-1 can't be upgraded, should you sell yours and get the Ultimate? If you want the best, and money is not a major factor, then of course you should. If, like most of us, you would like to have the best but must also consider the cost, then you have to weigh the benefits of having a better preamp vs improving some other part of the system. My guess is that, in most systems, an SL-1 Signature of whatever vintage is not likely to be the weak link. But...what if you can get a decent price for your preamp? Then you can get the Ultimate, and then you'll know it's not going to be the weak link. Oh, it's tough being an audiophile.
If you're ready and able to move up from an entry-level or middle-of-the-pack preamplifier, here's my recommendation: Put the latest CAT at the top of your short list. When you listen to it in the right system, you'll likely conclude that its moniker is entirely appropriate.—