When Clark Bedford founded the Pittsburgh Concert Chorale 25 years ago, he didn't even have money to buy sheet music for his singers.

"At the beginning we asked people to buy their own music," he says with a laugh. "Barry Miller and the Mendelssohn Choir were very nice and allowed us to borrow some scores."

Back then, the group was called the North Hills Chamber Singers and Mr. Bedford could only scrounge up 28 volunteer singers. But they were all committed to the art of choral singing. We just did it for the love of music. I wasn't paid anything."

Four years later the group incorporated as a nonprofit, and then in 1994 Mr. Bedford renamed it the Pittsburgh Concert Chorale. It is a success story of a community choir that has reached its potential and then some.

"The choir was thrilled to do most of Bach's B Minor Mass," says Mr. Bedford. "That was very memorable. We did some unusual things at times, [including] Amy Beach's 'Canticle of the Sun' here at Pittsburgh and then at Chautauqua."

In 1999, the group toured to the United Kingdom for six concerts including singing Evensong in a Cathedral in Cardiff, Wales, and it has twice performed at the National Cathedral in Washington, D.C.

Over the years, the Concert Chorale also has performed large works such as Mendelssohn's "Elijah," Handel's "Messiah" and a raft of requiems (of Mozart, Brahms, Rutter, Faure and Durufle). It has performed the premiere of Pittsburgher Glenn Rudolph's "Te Deum," Fr. Normand Pepin's "Obedient Unto Death" and arrangements of Fred Rogers tunes.

Under Mr. Bedford, the choir tripled in size (now numbering around 90), and its budget increased to around $100,000 -- enabling the group, among other things, to buy its own music. So when he decided he would retire in 2006, he wanted to make sure the choir would continue to thrive. That led to an unusual situation in which not only did the departing director helped to pick his successor, Katherine Mueller, but he shared a season with her in 2005-06 as co-music directors.

"Robert Page was a mentor to me," Mr. Bedford said of the esteemed choir conductor on the Carnegie Mellon University faculty. "He suggested Katherine Mueller."

She was studying with Mr. Page at CMU at the time.

"It was kind of an unusual situation -- usually someone leaves and someone comes," says Mrs. Mueller. "But it was Clark's group for so long and it was a very smooth transition. People got used to me [that season]. It was very positive and supportive."

Mrs. Mueller says the group's success starts with the level of singing. "It is an all-volunteer choir that is committed to professional level of performance. I am selective, and you can't get in if you just carry a tune." She will soon move to Winchester, Va., to attend Shenandoah University to get her doctorate in chorale conducting, but will continue to conduct the group.

The Concert Chorale performs pops and Christmas programs during the season, but for its 25th anniversary celebration, it has targeted one of the bigger works in the repertoire. Mrs. Mueller will lead the choir and the Academy Chamber Orchestra in Arthur Honegger's oratorio (he called it a dramatic psalm) "King David."

WQED-FM's Stephen Baum will narrate, soprano Katy Shackleton-Williams, contralto Daphne Alderson and tenor Dean Kokanos are soloists along with organist David Billings.

" 'King David' is the hardest thing I have done with the group," says Mrs. Mueller, and the recent snowstorms haven't helped the rehearsal schedule. But she knows that the character of the singers, established by Mr. Bedford, helps to ensure that it will come together in time for the concerts.

"These are the hardest-working people I have ever met," she says. "I think this group has a big future."

Critics Andrew Druckenbrod and Scott Mervis talk about music on "The Beat," available exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.