What a treat to sit close to live informal chamber music, so different from (say) Pollini in Symphony Hall or even the Emersons in Jordan Hall. With little fanfare last week, an enterprising and ambitious group of, well, by no means mere amateurs, but hardly all fulltime professional working musicians, gathered at Brandeis University, in Waltham, for a free Haydn quartet marathon. HaydnEnthusiasts, based around San Francisco, are united chiefly by love of Franz Joseph. None is involved with the Brandeis music department (one violinist is a chemistry professor there, researching HIV vaccines), and many of the rest have similarly non-music primary jobs. Only a few live on the East Coast; all pay their own airfare in pursuit of this beloved sideline.

This alum moseyed over Monday afternoon. With three venues and 45 hours or so of music over two separated days, nobody heard everything. First stop for me was the atrium of the Mandel Humanities Center, next to the old humanities center of a half-century ago. The acoustics were large and high, splendid of the type, and the dozen studying kids quiet, mostly. Any geezing ghosts of 1960s English and history majors remained in slumber. Violinists Andrew Wong (Enthusiasts co-founder, also MIT- and Stanford-educated software engineer) and Ryan Shannon (recent NEC grad), violist Justin Ouellet (recent Longy grad), and cellist Nicole Boguslaw (Bay Area freelancer) had just begun Op. 71 no. 1. It was sounding rough and ready, not professionally polished, but boy was it fresh and alive. And the informality can be a happy plus in this era of official concertgoing—restarts, chat between movements, smiling acknowledgments of minor screwups, bare feet, the occasional delicate sound of gum chewed. When they got rolling, with Opus 74 no. 2, it was the late 1780s all over again, with lively ensemble, precise violin intonation, pleasing confidence. With Haydn there is so much variety to attend to, so many forms of and occasions for sneakiness, vehemence realized and thwarted, soaring song, surprises real and fake. It is not just that the guy loved being sly, it came to him like breathing, but in so many ways. The Emperor, Opus 76 no. 3—many of the quartets have nicknames from the time, and the Enthusiasts have given funky new ones to many of the rest (Thou shalt not trill, Scales to Neverland, the Rabbi, and so on)—received a completely expert and solid reading, albeit with a somewhat timidly played last movement. So many features it has, so many effects it achieves, such a range of properties in the variations; one wonders what the 27-year-old Beethoven in 1797 made of its wonders. On a side note, the Emperor’s famous “Austrian” hymn is certainly not something ever heard on that campus back in the day.

Despite wanting to stay, since the students and occasional faculty in the space were dwindling to a half-dozen, I rolled downhill and across campus to the Shapiro student center, a necessarily noisier environment, with talkative traffic in a less enclosed acoustic, and alas more of a background-music vibe. Nonetheless, from the opening of Opus 55 no. 1, this quartet’s playing seemed a small step up, more practiced, with barely a few sour missteps by violinists Isaac Kraus (the chem professor, once upon a time a Haydn quartet rejecter) and Jason Sundrum (engineer at Facebook), and none I could hear from violist Elaine Leisinger (co-founder, UMass-Boston math prof) and cellist Shay Rudolph (BU grad now on Clark faculty; member of New Bedford Symphony, NH Philharmonic, Indian Hill, her own rock band; toured with Star Wars: In Concert).

Opus 64 no. 2 has a famously quiet, exhaled ending. Passersby stopped. Opus 64 no. 6 was the high point of my stand along this marathon route. It opens with measures of unusual loveliness, a throwback, it felt to me at the time, though to what I do not exactly know (Cimarosa? one of the Bach kids?). From there the ensemble romped and raced and danced like it was 1790 and brand-new but already well-known. In fact every passage went easier in this one. In the second movement, Krauss’s solo work, very high, was immaculate, as was Sundrum’s in the third movement. And it was taking place, flying by, only a few feet away: tremendously exciting.

As noted, this all represented the tip of the Haydn string quartet iceberg. Be sure to keep an ear out for these guys, the HaydnEnthusiasts.

David Moran has been an occasional Boston-area music critic for 45 years, with special interest in the keyboard.