Robert Koff; violinist, professor cofounded Juilliard quartet; at 86

For six decades, Robert Koff taught generations of young musicians here and abroad to love the violin as much as he did, and to play it from the heart. ''Forget about the technical things," he would urge. ''Play it as if you were telling a story."

A founding member of the famed Juilliard String Quartet at New York's Juilliard School, Mr. Koff practiced what he preached. ''Robert's playing was beautiful and effortless, as if he was speaking directly to you," said Judith Eissenberg of Brookline, who plays violin in the string quartet Mr. Koff formed at Brandeis University 26 years ago.

Mr. Koff, a celebrated professor of music at Brandeis for 25 years, died Tuesday in his Lexington home from a rare blood disease. He was 86.

In 1980, Mr. Koff persuaded Brandeis to support a new string quartet, naming it the Lydian Quartet, or the Lyds. With Mr. Koff's guidance in the quartet's early years, the group went on to win prizes in international competitions. It is still performing today.

After he retired from Brandeis in 1983, Mr. Koff coached a variety of chamber music ensembles -- from groups of doctors to young students and professionals and at the New England Conservatory and Longy School of Music in Cambridge.

Mr. Koff remained a passionate teacher to the end, said his son, Stephen of Los Angeles. Two weeks ago, he was giving a lesson to one of his students from the Intensive Care Unit at Beth Israel Deaconess Medical Center.

Beth Israel physician Tom Delbanco, a Lexington neighbor and violin student of Mr. Koff, played for him in the ICU. ''Bob was the ultimate teacher. . . . No matter what the level of talent, he'd push, prod, cajole, and stretch students until they outdid themselves," Delbanco said. ''He was always experimenting, whether with different ways to express a musical idea, electronic gadgets, his garden, a bad joke, or a fantasy that he wrote in French."

Mr. Koff did it all with a sense of humor. ''One of the things his students loved best about him was that he made education fun," said Mr. Koff's wife, Rosalind (Mann), a Juilliard-trained pianist who performed with her husband.

''Bobby had a unique ability to 'talk' as he played. He was one of the most natural, expressive musicians I ever encountered," said pianist Sally Pinkas, a professor of music at Dartmouth College whom the Koffs arranged to bring to Brandeis from Israel in 1976. ''There was nothing studied or artificial or pretentious in his music-making," Pinkas said. ''He played as he was, an incredibly generous, intelligent, whimsical person."

Mr. Koff was born in Los Angeles, an only child. He began studying the violin at age 5 after a teacher told his father he had the hands and the temperament to become a great violinist, his wife said.

While in high school, Mr. Koff was concertmaster in the Los Angeles Youth Symphony and won many high-level competitions, his son said. He went on to the Oberlin Conservatory.

He graduated from Oberlin in 1941 and enrolled in the Juilliard Graduate School. He left Juilliard to join the Army in World War II and was assigned to the band; he played tenor tuba. After the war, he returned to Juilliard and graduated in 1946.

While at Juilliard that year, Mr. Koff and fellow student violinist Robert Mann decided that the school should have a resident quartet. ''The Juilliard Quartet had an enormous impact on classical music," said Laurence Lesser, retired president of the New England Conservatory. ''In the middle of the past century, they, along with the Budapest Quartet, and the Beaux Arts Trio, established chamber music as a legitimate career path for the most talented musicians. No longer did such individuals have to focus on becoming soloists."

While at Juilliard, Mr. Koff met Rosalind, who was studying piano there. They were married in 1947. He taught at Juilliard from 1946 to 1958. In 1958, his wife said, he was invited to be professor of music at Brandeis.

Daniel Stepner of Newton, a violinist with the Lydian Quartet for 18 years, recalled visiting Mr. Koff two months ago. ''Though he was physically weakened, he was his old feisty self. He was playing the violin again," he said.

But that wasn't surprising, Stepner said, because Mr. Koff ''kept a kind of boyish enthusiasm and approach all through life."

His son added, ''He created such a passion for life through his music."

Besides his wife and son, Mr. Koff leaves two other sons, Daniel of Sebastopol, Calif., and Jeremy of Los Angeles.

A memorial service is planned, his wife said.