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Grammy-winning fingerpicking guitarist Pat Donohue thinks a South Dakota college town of about 10,000 is an unlikely place for a wide-ranging collection of musical instruments that includes saxophones built by inventor Adolphe Sax, a rare Stradivarius violin with its original neck, and a Spanish guitar on which Bob Dylan composed some of his earliest songs.

But that's part of the charm of the 40-year-old National Music Museum, a treasure tucked away in an old Carnegie library building on the University of South Dakota campus.

Donahue, a regular performer on Garrison Keillor's radio show "A Prairie Home Companion," got to play a 1947 D'Angelico New Yorker guitar and a 1902 black and wood-grained guitar built by Orville Gibson for millions of listeners during a 2006 live broadcast from the campus.

"The only unfortunate thing that I can think about it is that not enough people are going to see it because of where it is," Donohue said. "But then again, that's one of the things that make it unique."

The National Music Museum has boasted a world-class collection of musical instruments since it was established, and officials now want to build a facility to match that. The museum is looking to raise $15 million over the next few years to triple its gallery space, improve the entrance and revamp the vast archives where music scholars can peruse the thousands of instruments and documents not on public display.

"We'll have a proper lobby and visitor reception area, which we really don't have now," said Ted Muenster, who's leading the fundraising effort for the USD Foundation. "It will be a pretty impressive complex when we're finished with it."

The expansion plans recently earned a federal seal of approval with the awarding of a $500,000 challenge grant from the National Endowment for the Humanities. Endowment chairman Jim Leach visited the museum in 2010 and found its collection of more than 15,000 items "astonishing."

"This is a national treasure," Leach said. "It could just as easily be called the International Music Museum as the National Music Museum. It is one of, if not the, centerpiece of musical instrument collections in the world."

Cleveland Johnson took over as the museum's director in November after the retirement of Andre Larson, who'd been at the helm since it was established in 1973. The holdings grew out of a private collection owned by Larson's father, Arne B. Larson, who continually added items while serving as a public school music director.

The 800 or so instruments on public display are the "superstars" of the broader collection of pianos, harpsichords, guitars, horns and drums.

A keyboard aficionado could marvel at a Neapolitan virginal and harpsichord from the 1530s or the earliest French grand piano known to survive, an ornate green and gold instrument built by Louis Bas in Villeneuve lGes Avignon in 1781.

A fan of stringed instruments would gasp at "The King," the world's oldest known surviving violoncello, which was crafted in 1545 and played by King Charles IX of France in 1562.

"What gets you through the door is a particular interest of yours," Johnson said. "What keeps you here twice as long as you planned are all the unexpected discoveries that you make."

Johnson hopes the expansion and a ramped-up marketing effort will bring more tourists to Vermillion, but he also wants to boost the museum's loans and traveling exhibits to get more exposure. The museum's red, silver and blue tenor saxophone -- donated in 1994 by President Bill Clinton -- was recently displayed at the National Constitution Center in Philadelphia.

"We could double our attendance, but we're still talking about a few tens of thousands a year," he said. "It's not so much getting people through our doors as getting our collection in front of the eyes of people."

The museum scored its greatest public exposure during the "A Prairie Home Companion" broadcast. Museum officials even permitted the playing of "The King" violoncello on air, though such special occasions might happen "maybe once every generation," Johnson said.

It's a decision made on a case-by-case basis, balancing the rarity of the instrument, its condition and the potential audience reach, he said.

Leach said the National Endowment for the Humanities grant is designed to bring in $3 in private donations for every $1 from the government. It also gives the museum a little street cred in cultural circles, since all applications for funding are peer-reviewed.

"We only fund one out of six, and they're all assessed by and graded by experts in fields," Leach said. "This got a wondrous review by a panel of the world's leading experts in not only museum studies but music studies."

Expansion plans call for adding about 65,000 square feet (6,000 square meters) of gallery space to the existing 23,000 square feet (2,100 square meters). The limited space has not only prevented instruments from getting their proper display, but also has hampered curators' efforts to find creative and hands-on ways to program and teach visitors and school groups, Johnson said.

"The new building is still years away," he said. "I'd imagine it will be fully used the minute they cut the ribbon."