In fairness, violinist Nancy Wilson warned us there would be tradeoffs.

The instruments the Classical Quartet plays, she pointed out Saturday at the Musuem of Fine Arts, are not the typical modern variety. Rather, they have been restored to their pre-19th-century condition.Among other things that means shorter necks and no chin rests for the violins and viola, looser reinforcements inside, gut strings as opposed to steel and shorter, lighter bows. The result, she said, was that they might not project as strongly as what we are accustomed to hearing, but there would be greater flexibility and transparency of texture.

Certainly the sound itself was less insistent, drawing the listener in rather than forcing itself out. Neither was it abrasive, as often happens with period-performance groups, thanks to the more sparing use of vibrato.

But would that have accounted for the frequently sour intonation and occasional wrong notes that disfigured these performances? Or the lack of vitality in the playing itself, generally lethal in Mozart?

What's more, this program was all Mozart, ranging from the early B flat major Divertimento, K. 137, (which may or may not have been conceived for string quartet) to the K. 590 Quartet in F major, the last of the "Prussian" Quartets. But where with most period performances of my acquaintance the music tends to leap off the page, with new resiliency and inner life, here it just lay there, delicate but moribund.

In short these players pretty much chloroformed these pieces, and came close to putting me to sleep as well. Nor did things change much after the two violinists traded places at intermission, putting Linda Quan in the first chair. As with the finale of the K. 387 Quartet, there may have been a bit more animation - just a bit. But one still noticed the scrapes and intonational problems, especially on the low end (e.g., the exposed viola writing).

If this were simply a question of interpretative differences, so be it. But I fear some people may have gone away thinking it was the instruments themselves that were to blame, and I don't believe that.

Admittedly we don't get many 18th-century groups through here, but this was not the case with the program the now-defunct Amade Trio presented in this same building a decade ago. Nor will you hear it on any of the recordings Jaap Schroeder or Simon Standage have been associated with in recent years.

Nor is it inherent in the music. But I wonder how many, had they been hearing it for the first time Saturday, would have recognized the greatness of the K. 387 - the first of the six quartets dedicated to Haydn - with its unconventional harmonies and breathtakingly contrapuntal finale. Or that in the K. 590 it is the outer sections of the minuet that contain the meat and not the trio, something only hinted at here.

Here by contrast it was the Allegretto (the movement's original marking) that came off best, thanks to the aforementioned delicacy and a not-too-slow tempo. But there is more to Mozart than that, and that must have been apparent even in his day.