The Electro-Harmonix Bad Stone is a phase shifter guitar effect stompbox pedal that is an updated version of the popular 1970s Bad Stone pedal. The pedal is faithful to the original circuit design and three-knob control layout, but features up-to-date enhancements for the modern player.

The Bad Stone delivers six stages of phase shifting plus a manual mode that lets the player freeze the phase. Its Rate knob controls the phase shifting speed which goes from a very slow swoosh to a rapid, oscillating warble. Feedback determines the depth of the phase effect and a toggle switch lets the user select Auto or Manual modes.

In addition to the die-cast package, other modern amenities include true bypass for maximum signal path integrity, an effect status LED and an AC jack that accepts an EHX9.6DC power supply. It also can run on a 9V battery (included).