Provided is a modular string instrument including a core string instrument and interchangeable instrument body types. The core including: a core shell forming a basic shape of the core string instrument, a string instrument head, a neck base, a chassis assembly configured to be inserted into the core shell, extending from the head to the neck base and comprising a strings anchoring bridge, a plastic fret board configured to have frets attached thereon, the fret board configured to cover the core shell and to encase the chassis assembly within the core shell, a neck base cover configured to be attached to the neck base, a pickup cassette bay configured to encase an interchangeable pickup cassette, and strings stretched from the bridge over the pickup cassette bay, over the neck base to the head.