The object of the combination action is to make possible instantaneous registration changes involving many stops, at the press of a single piston. This is of particular importance in theatre organ music where tonal variety is required.
A system of electro-mechanical control is used by which pistons, when pressed by the organist, bring ‘on’ certain stops and put others ‘off’ (a ‘combination’). Each piston brings on a specific combination, each of which is pre-set by the organist using either a setter-board containing rows of switches, or a setter button operating an electro-mechanical or electronic system (nowadays) which memorises the combinations being set.
The essential parts of the combination action are, therefore, means of:
• Remembering the combination settings (combination memory).
• Signaling the need for a combination change to the combination memory (the pistons).
• Driving the stop-keys on and off (the stop action).