Tube Preamp Reviews

The balance control could have finer increments, and the power supply is hard-wired to the main preamp unit. All in all, however, the ergonomics are very good, and cartridge loading is easily changeable through plug-in resistors or capacitors. I would have liked another high-level input, but then reviewers always want another high-level input—perhaps their only area of consistency.

The Sound: Comparing the SL-1 With the Best
The sound of the Convergent Audio SL-1 is very good indeed (as it should be at $3495)—good enough that it can probably be best reviewed by comparing it to its top competition. The Audio Research SP-10/II and SP-11 are obvious standards of reference in tube design, and the original and revised Motif MC-7 are good transistor standards of comparison.

Bass: The original Motif MC-7 had excellent bass and lower midrange, with an emphasis on control rather than sheer bass power and dynamics, and the revised MC-7 is as good, and possibly superior in detail. The Audio Research SP-10/II is a very close rival to the MC-7. The bass is slightly less extended, but the SP-10/II has a faster and more dynamic way of handling bass instruments. The difference between the two is like shifting from midway in an orchestra hall to listening quite close to a small jazz group.

The Audio Research SP-11 has a notably different sound character. While the revised MC-7 is perhaps a bit too rich and warm in the transition area between bass and midrange, the SP-11 is extremely transparent and extended in the deep bass, without a touch of extra bloom or control loss; it's just a touch too lean, however. The C.A.T. SL-1 is very similar to the Audio Research SP-11 in this respect, with perhaps a little more overall energy.

Upper Bass/Lower Midrange: Both versions of the Conrad Johnson MC-7 make a smooth and coherent transition from bass to midrange. Once again, however, the MC-7 is a bit less dynamic and "live" than the Audio Research SP-10/II. The SP-11 and the Convergent Audio Technology SL-1 are similar to the Motif MC-7.

It is important to note that this region is one of the SP-10/II's great strengths in reproducing recorded music: it makes most music seem more natural in this area than the SL-1 or SP-11. The SP-10/II has the musically natural smoothness of the Motif MC-7, but is more naturally dynamic and has more life.

This is a damn good reason to not trade in your SP-10/II, if you were considering such a thing. The upper bass and lower midrange are transition areas that on much equipment seem to lack character and musical detail; when really good equipment comes along it makes you remember that this is the area where all music packs a great deal of its power and emotional impact. All of the preamps involved in this comparison do well in this region, but the Audio Research SP-10/II outperforms every preamp I've heard in this key performance area.

Midrange: All four preamps provide superb performance in the midrange. They should, and no audio equipment is worth a damn that doesn't. The SP-11, however, performs best, with the Convergent Audio Technology a close rival. Both the older and newer versions of the Motif MC-7 are just a bit too soft and mid-hall, while the SP-10/II is slightly too warm and romantic. The SP-11 seems spot on, and is amazingly revealing in this part of the frequency spectrum. The SL-1 has much the same tonal character as the SP-11, but lacks a bit of its natural dynamic energy.

Upper Midrange: All four preamplifiers sound very different in this area, but all are very listenable and musically involving without producing artificial emphasis or fatigue. The new version of the MC-7 has the added energy and life missing in the early version. The SP-10/II is just a bit too warm. It makes most recordings sound too good: a fully accurate preamplifier would reveal more detail, without any more emphasis of the upper midrange than is musically natural.

The C.A.T. SL-1 seems exceptionally accurate. It does an outstanding job of reproducing what is on the LP or CD, good or bad. Once again, however, the Audio Research SP-11 seems superior in terms of overall tonal accuracy, dynamics, and detail—particularly in soft passages. It would be nice in some ways, however, if the SP-10/II were accurate; it makes most recordings sound like music. The SP-11 and SL-1 reveal the unfortunate fact that most recordings sound like recordings.

The Treble: The original MC-7 was just a bit short in the highs. The improved MC-7 is excellent, with slightly less energy than the SP-11 or SL-1, but all the treble information and detail anyone could desire. The sound is slightly soft in comparison with most transistor preamps, but everything in music is present in the MC-7, and the MC-7's highs are very well integrated into the overall sound.

The Audio Research SP-10/II is more forgiving than the MC-7, perhaps a little too forgiving. It again makes recordings sound a bit too much like live music, and a little less like recordings, than it should. It is also slightly lacking in low-level detail in this area, with more air and apparent life in the treble on most material than is really justified.