Shares in Guitar Center Inc. gained nearly 20 percent Wednesday after the company said it had agreed to be bought by a private equity firm for $1.9 billion in cash.

The deal is with affiliates of Boston-based Bain Capital Partners LLC and came amid speculation that a buyout was in the works. Guitar Center hired investment bank Goldman Sachs & Co. to auction the company back in May. The deal also includes $200 million-worth of debt.

Bain Capital offered $63 per share, which represents a 26 percent premium over Guitar Center’s closing price June 26 of $50.06 and a 33-percent premium on the Westlake Village-based retailer before talk of a sale began to circulate. The purchase price is based on the company’s 30 million shares outstanding at the end of March.

The deal, which requires approval by Guitar Center shareholders, is expected to close in the fourth quarter.

Marty Albertson, Guitar Center’s chairman and chief executive, said in a statement that the deal “is a strong validation of the company’s accomplishments over the years as well as our future growth prospects.”

The sale comes nearly two months after the music equipment retailer posted double-digit growth in profit and sales for the first quarter. The company owns and operates more than 210 stores and has seen shares more than triple since its initial public offering in 1997.

Shares in Guitar Center jumped 19 percent, or $9.41, to $59.47 Wednesday in afternoon trading on the Nasdaq.