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The first Sigmas were typically dreadnought acoustic, although Grand Concert Series (GCS) and classical models were also produced from the early 1970s (1971?) onward. Sigma released a wide series of acoustic and classical guitars, which initial construction was in Japan by various manufacturers/factories from 1970 through 1983. Martin created the brand "Sigma" in order to compete with cheaper guitars that were imported from Asia.
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The Sigma line was discontinued by Martin in 2007. Martin as a line of guitars at affordable prices to compete with the increasing number of imported guitars from Japan and elsewhere.
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Sigma Guitars is a guitar manufacturing brand originally released by C.F. Acoustic and classical guitars, acoustic basses, ukuleles