Convergent Audio Technology SL-1 preamplifier Page 4

The SP-10/II can be switched in a number of ways to reduce coloration in the high gain stages, and seems remarkably neutral (until you hear the SP-11). It does, however, add a bit of warmth and apparent imaging detail to everything that passes through it, with this coloration increasing in direct proportion to gain. The phono stage is very consistent with the overall character of the high gain stages, and its sound character doesn't change with cartridge loading, but its gain capability is also clearly marginal with many of the lower-output moving coils. It needs a relatively high output mc, like the Koetsus and Kisekis, and the gain match can be unpredictable. It works very well, for example, with the Monster Cable Alpha 2, but not with the van den Hul MC-10—though both my samples measure as having the same output. Using a moving coil with output too low, the SP-10/II can suddenly seem to lose energy in the bottom four octaves, lose some of its dynamics, and add a hint of noise.

The SP-11 is probably the most neutral and flexible preamp ever made at every combination of its gain stages. It is sonically consistent with all but the very lowest output moving coils (such as the Audionote and Ortofon MC-2000). At the same time, there are a wide range of combinations of gain, allowing you to remove small amounts of coloration, but at the cost of also removing what are often very necessary and useful features (see JGH's review in Vol.9 No.4).

Most audiophiles will be far better off if they leave in the gain stages that include the balance control, since precisely balanced power response is virtually unheard of in real-world listening rooms. Incorrect balance is far more damaging to the imaging and soundstage than the slight loss of transparency introduced by the balance control and extra gain stage. At least half the time the user will also be better off using the high-level gain stages to create a proper gain match and suitable buffering between high-level inputs and power amp. It is easy to trade one form of coloration for another, and, while transparency may benefit, the wrong match will restrict dynamics and slightly slant the overall timbral balance in favor of the upper octaves.

The Convergent Audio Technology does not have all of the gain-stage bypass features of the SP-10/II or SP-11, but it does have a remarkable consistency at every level of gain, regardless of moving-coil loading—as long as the cartridge output is suitable (see above). It sets an exceptional standard of transparency at every gain level, with just a slight compression of dynamics as you shift from high level inputs to phono.

Not Ranking the Top Preamps: Hoos on Filst?
Given this level of performance, it is clear you can welcome the Convergent Audio Technology SL-1 to the ranks of the top contenders. You also can probably do a little to tailor its sound to your taste. This is a tube unit, and if you don't think that different brands of tubes have different sound characters, then you simply haven't listened.

I'd recommend that you talk this over with your dealer or Ken Stevens. Ken gave me an assortment of different tubes to try, and they made a number of subtle differences. I strongly suspect that you can improve the match between the SL-1 and the rest of your components by simply getting the right brand of tubes. While every designer I know insists that transistors with the same designation also sound different, you can't plug them in and out.

But please understand what I am recommending: get your tubes from Convergent Audio Technology! In fact, long and painful experience has shown me that you should always get your tubes from the preamp's manufacturer. You are likely to get the SL-1's excellent signal/noise ratio only if you do, and no audio equipment manufacturer I know of has found a source of tubes that is good without extensive screening and rejection of bad or mediocre samples. Worse, if you want to know where many of the tubes sold by independent "high-end" purveyors come from—at least some are manufacturer rejects.

As for the vital question of how to rate the four preamps? Well, the latest version (footnote 2) of the ARC SP-11 still defines the state of the art—as well as the state of the price tag! For the purposes of this review, however, what's important to know is that the C.A.T. is good enough to compete head on with the best, and offers a new and important blend of sonic qualities.

You can't have everything in one preamp; if you feel that a Porsche should also be a Rolls Royce, then no preamp will meet your needs. At the same time, if you want a preamp that will help you extract natural musical pleasure from a wide range of recorded material, then all four of the units discussed here can do an excellent job. At this level of quality, the question "Who's on first?" is strictly for Abbott and Costello.

You don't need someone else's opinion to make this kind of decision for you once you are pointed in the right direction, unless your ears are truly gutless. You need to listen, then match your choice to the rest of your components to keep your system consistent and synergistic. It is not, for example, a good idea to use a Motif MC-7 with an Audio Research tube power amplifier, or vice versa. After all, mixing the best red and white wines does not result in getting the best taste and bouquet of both types of wines, it only results in the sonic equivalent of Sea Cliff Rose—and you all know about the problems in wines produced from the slopes of the lower east side of New York!

Footnote 2: This latest version of the SP-11 is an unannounced in-production update that AHC received after most of the listening for this review was completed.—Larry Archibald
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