Same time, next year is a familiar refrain to the four members of the Tetzlaff Quartet. For the last 18 years, the foursome, headed by superb superstar German violinist Christian Tetzlaff, has regrouped to tour and play “pieces of greatness that are not the most known by the public,” as Tetzlaff put it in a recent phone interview from Boston. The group’s tours are short affairs. The U.S. tour that brings them to Ann Arbor’s Rackham Auditorium Saturday, for example, has but eight dates. In between, the members — who include Tetzlaff’s sister, the terrific cellist Tanja Tetzlaff; violinist Elisabeth Kufferath and violist Hanna Weinmeister — go their busy solo, chamber music and orchestral ways. But they’re linked by kinship, fellowship and long acquaintance. All four are the original quartet members.

“We’re not comparable to other quartets,” violinist Tetzlaff said. “We’re not continuously playing. We basically get together to have the opportunity to play those fantastic pieces again.

“Of course, we don’t get tired of each other since we rarely play together. For other quartets, it can be difficult to sit, rehearse and travel together every week for 30 years. Already, for two people to live together so long is difficult. We don’t have that.”

The “fantastic pieces” that the quartet presents here include Haydn’s Quartet in g minor, Op. 20, No. 3; Mendelssohn’s Quartet in a minor, Op. 13 (“Ist es wahr?”); and Sibelius’s Quartet in d minor, Op. 56 (“Voces Intimae”).

The “intimate voices” of the Sibelius, as Tetzlaff noted, are not specified, though “the slow movement speaks of deep personal things.” The Mendelssohn, based on the composer’s song setting of a poem by Johann Gustav Droyson, is a different story.

“Mendelssohn says what the intimate voices are,” Tetzlaff said. “The unfulfilled love affair, the song throughout the whole piece.”

Tetzlaff said that he thinks of chamber music as a seamless part of his career, which is still dominated by solo appearances with orchestras. The soloist, he said, must always think of the links to the orchestra, or something is missing.

Quartet playing, he added, is as taxing in its way as solo work.

“To play a violin concerto by Mendelssohn or anybody is hard, but the violin parts of string quartets are also demanding and difficult. It demands a whole different stamina than playing a violin concerto.”

And Tetzlaff likes the change of pace.

“I always mix everything anyway,” he said. “I have no plan. I only like it if it’s diversified.”