'When all goes wrong . . . smile a lot."

Such was the advice that conductor Scott Terrell gave to the everyday people who stepped up to lead a Philadelphia Orchestra contingent Monday at the Reading Terminal Market. Orchestra players have performed pop-ups from Macau to the Comcast Center, and Monday morning word went out on the Internet that this one would be a "Conduct Us" program, where listeners could become participants and get a souvenir baton.

No way the entire orchestra could fit at the northerly end of the crowded market, of course. But right under the sign for Spataro's Cheesesteaks, 11 string players clustered for an hour of Mozart's Eine Kleine Nachtmusik and Dvorak's Serenade for Strings. The guest conductors ranged from tourists to local amateurs.

"I play guitar and ukelele, but orchestra? I've looked at them," said University of Pittsburgh engineering student Max Tate, 20, who is home in Philadelphia for spring break. "A lot of engineers are musicians. It stimulates . . . the creative side of the mind."

Kristie Nies, 57, visiting from Tennessee, seemed to know the right beats for Mozart's time signatures but got lost and flustered, at which point Terrell gently stepped forward to guide her hands. Nobody was expected to be expert, which was part of the fun.

"The market needed somebody to laugh at. I didn't know what I was doing, obviously," said Moses Smucker, a 64-year-old Amish man from Morgantown who runs Smucker's Quality Meats & Grill - and who could conduct the low-tech orchestra without going against the principles of his lifestyle.

But maybe the conducting guests knew more than they thought. "One of them had a beat that was clearer than Valery Gergiev's," said violinist Davyd Booth of the noted Russian conductor who recently led the Philadelphians at Verizon Hall.

The concert came during a busy time for the ensemble. During the same 24-hour period, it played a recording session on Sunday for the prestigious Deutsche Grammophon label, with Yannick Nézet-Séguin and the increasingly celebrated young Russian pianist Daniil Trifonov. Though the repertoire was Rachmaninoff's 25-minute Rhapsody on a Theme by Paganini, the session took six hours.

Monday's concert (which wasn't a debut - a string quartet from the orchestra played the market in 2011) was the first in two weeks of outreach performances that will include student concerts at schools in Bensalem, Norristown, and Northeast Philadelphia. But few spots can boast the cross-section of humanity that the market can.

"This is a good location to put the message out there," said violinist Amy Oshiro-Morales, "to say this is some of what we do, but not all."

The acoustics were inevitably challenging. "I was playing so loud to get over the noise, it reminded me of the times when we used to take our cars out on the freeway and drive 80 miles an hour to blow out the carbon," said cellist Richard Harlow.

Yet the players hardly lacked for outside participatory energy.

"Sitting here, you hear the rhythm of the music and the rhythm of the cheesesteak people," observed Richard Greene, 75, a retired Temple University professor sitting between Spataro's and the players. "And sometimes they coincided. Particularly during Mozart."