Twenty-six years ago, when Stephen Osmond first, conducted Bach's "Brandenburg Concerto No. 2," it was a disaster.  He was guest conducting at the Westboro Summer Chamber Music Festival in San Francisco.  The featured trumpeter, from the San Francisco Symphony  fell apart.  "The first rehearsal, the guy. did well," remembers Osmond, veteran maestro of the Jackson Symphony Orchestra. "  The second rehearsal, he missed about 10 percent of the notes.  "By the time he got to the concert, he couldn't play half of them."

Perhaps that explains why Osmond refers to the Bach concerto as "the most treacherous instrumental piece I know of."  Perhaps that also explains why Osmond went after Scott Thornburg to play it Saturday night.  When it comes to playing the piece that many trumpeters wouldn't even attempt, Thornburg is a master.  He figures he's played the piece about 40 times over the past 15 years, with chamber ensembles and orchestras all over the world. In fact, Thornburg performed it just the other day with a chamber group in Gainesville, Fla.  He'll be in the spotlight again Saturday night, when the JSO performs its second subscription concert of the season. 

"Basically Bach and Totally Baroque" begins at 8 p.m. in the Potter Center's Harold Sheffer Music Hall at Jackson Community College.

Bruce Brown, a Spring Arbor University music professor and the symphony's composer-in-residence, talks about the Bach piece, as well as other music and composers on the program, during his popular "Backstage Glimpses" session an hour before the concert.

The concert, featuring what Osmond calls "an incredible amount of variety," includes the symphony teaming with the Jackson Chorale for Bach's "Cantata No. 4," and JSO concertmaster Michael Heald showcased on two of Vivaldi's "The Four Seasons" movements, "Spring" and "Winter."

Heald, who took over the concertmaster post when Phil Mason retired last season after 40 years with the symphony, has "passed every conceivable test we have given him, both musically and non-muscially, which is a very important part of the job," Osmond says.

As far as the Bach piece is concerned, Thornburg has passed all the tests, too.  Still, "it's like training for a race. I feel like I have to get it worked up each time," says the soft-spoken Thornburg, 42, on the phone from his office at Western Michigan University in Kalamazoo, where he is a music professor.  "What it demands physically is really different from the other trumpet playing I do, I have to get it back each time,"

The difficulty of the piece, Thornburg says, is in reaching the extreme high register, requiring "a lot of finesse and the ability to deliver great technical details in a register that. is really hard to do."

Thornburg, a Juilliard graduate and member of the New York Trumpet Ensemble, joked that he's not even sure what kind of trumpet Bach had in mind when he wrote the piece.

"Ideally, it shouldn't sound hard. There are four soloists on the piece: oboe, flute, violin and trumpet. I'm supposed to be in the same range as they are.  "But that range is almost off the charts at times."