Busbar

Each Hammond key has 9 thin metal leaf switches, one for each of the nine harmonics on the drawbars. There are 9 conductive busbars, stacked vertically and insulated from each other, running underneath each keyboard. The busbars are stacked from the Sub Fundamental on the bottom busbar to the 8th harmonic on the top in the same order as the drawbars are arranged from left to right. As the key is pressed, each switch connects the proper tone for that harmonic on that key to its corresponding busbar. The busbars are then connected to the drawbars, which control the level of each harmonic. If a drawbar is pushed all the way in, any switch on the keyboard which closes on that busbar will not include that harmonic in the tonal mix.

Because there are nine switch contacts under each key and the key rotates through an arc, all nine switches _do not_ close simultaneously. They close somewhat sequentially (and not necessarily in the same order). Which means if a key is "bounced" or "slipped" and not depressed to close all its switch contacts to their busbars, some harmonics may not be heard. This actually enhances the "organic" sound of a tonewheel Hammond. Most clonewheel Hammonds lack this "feature" which is another reason they sound somewhat sterile.