At the top, there are five tones which ‘go off the top’ of the generator and are folded back onto the top octave provided. The lowest note has its sub-fundamental folded back, even though the tone generator goes low enough, represented by the width of the grey bars. The diagram below shows the effect of the harmonic foldback on the top and bottom notes of the keyboard.
The quirk is that the lowest octave of tonewheels are cut with a more complex shape and provide a waveform that is closer to a squarewave, with some 3rd and 5th harmonics present. Since the lower tones that are folded back are actually present in the instrument for the pedals, it is possible to rewire a Hammond for true bass, with no lower foldback. Note that the 6th and 8th harmonics actually repeat some tones twice. The 8th harmonic is repeated from tone 44, G in the fourth octave. The 7th harmonic repeats from tone 49, the lower C of the top octave. The 5th harmonic repeats from tone 52, D# of the top octave. The 4th harmonic repeats from tone 56, G of the top octave. This is shown in the following table, which shows the tonewheels (1-91) used for each harmonic It affects the 3rd and subsequent harmonics at the top, and the sub-fundamental harmonic at the bottom. Harmonic foldback is used to reduce the required number of pitches at both ends of the keyboard.
The 5⅓’ footage is oddly placed as the second drawbar, rather than in its logical position between the fundamental and 2nd harmonic, presumably because it is labelled as the ‘sub-3rd harmonic’. This pitch is provided by the 3rd drawbar, the fundamental. The basic pitch of the instrument runs from tone 13 to tone 73. The harmonics, footages, and notes used on the Hammond drawbars are shown below:Īs can be seen, for each note, the harmonics go three octaves above it, and one octave below.
Perhaps one day I’ll build a “clonewheel” organ, but then again, Clavia might have nailed it! Still, building an organ would be a nice project. My personal slant is towards copying this sound using other technology. This page is intended to be a look at some of the key technical aspects of the B3 Hammond organ that contribute to the “Hammond sound”.