When a performing group uses original instruments, its sound is necessarily "different" from that of "contemporary" ensembles. The Smithson String Quartet seems to rely on a combination of the instruments' physical characteristics and its own streamlined reading of the score for its particular musical product. Last night at the Hall of Musical Instruments in the Museum of American History, the quartet traded in the bright quality of some groups for their own brand of structural illumination.

The evening's most cogent playing came last, in Beethoven's A Major Quartet, Op. 18, No. 5. From his first creative period, the work hangs on to traits of Mozart and Haydn while the composer tries -- not so timidly -- to stretch his wings. The Smithson players held the piece at bay, restraining the rubato and tightening the articulation. The third movement's simple bass line structure was crisp and even, and the overall result was a trim, crystal-clear texture.

Mozart's D Minor Quartet, K. 173, was less steady and secure. In the opening movement, the ostinato phrases were sometimes rushed and the tempo lagged in the middle of both the first and second movements. The spritely fugue in the closing section was uninhibited and lively.

The group appeared well-collected in Haydn's Quartet, Op. 77, No. 2. All four movements were taut and unified. Especially nice was the Andante's gradual accumulation of momentum before the final, subtle release.