A Guitar Center Inc. shareholder contends that directors are shortchanging investors by accepting a $1.9 billion buyout bid by Bain Capital Partners LLC, a lawsuit contends.

Company directors failed to properly seek higher bids for the nation’s largest retailer of musical instruments, investor Mary Benton said Friday in her Delaware Chancery Court suit.

Bain on June 27 offered $63 a share in cash for the company, 26 percent more than the stock’s closing price the day before. The buyout firm would also assume the company’s debt, bringing the transaction’s total value to $2.1 billion.

The board of Westlake Village-based Guitar Center violated legal duties by “conducting an inadequate and unfair sale process,” Benton said in the complaint.

The suit contends that Bain’s offer is loaded with provisions designed to scare away other bids, such as $58 million breakup fee if Guitar Center accepts another offer.