After the short lived run of the JCM900 Mk III, that amp was redesigned into the SL-X series in 1993. The two amps lines share the same control panel layout as well as model numbers, but they are quite different in sound and function. The main principle is the same - a single channel amp, with two master volume controls, and more gain provided to capitalize on the popular hot-rodded and modded Marshalls of the time.