X 66

As we continue through the inside of a Hammond X66 console, we find this interesting array of colored wires attached to various screw terminals. To anyone who has seen the interior of a regular Hammond, this will be somewhat familiar. This picture shows the preset panel which is really an array of terminal strips where the various harmonics of each preset key are connected. Unlike many conventional electronic organs, the preset keys, which in a sense are equivalent to stops on a normal electronic organ can be set up by the technician to represent any possible tonal combination that you can set up on the drawbars.

This assembly is located on the underside of the control panel assembly where the stop tabs and drawbars are located. Because the control panel assembly is hinged, it is shown vertically here. Normally it is horizontal, and the preset panel is on the underside, but here we show it in the technician's access position. Each of the colored wires represents one of the harmonics for its associated keyboard and preset key. The horizontal metal terminal bars or strips represent from bottom to top an increasing signal strength.

In the X66, the seventh and ninth harmonics are paired; one wire represents both. The same is also true for the 10th and 12th harmonics. Because these harmonics are derived from the tempered scale, some of them are not quite exact. Ever since he designed his first instrument, Laurens Hammond had left out the seventh harmonic, because the TRUE seventh harmonic for any given pitch is about 30% flatter or lower in pitch than the closest tempered scale equivalent. For C, for example, the seventh harmonic's true pitch lies between A and A#, but it is closer to A#. When the folks at Hammond designed the X66, they decided to include the seventh harmonic which, although 30% too sharp because it's derived from the nearest equivalent pitch in the tempered scale, is still very useful.

However, in the case of the 11th harmonic, the true eleventh is 49% flatter than the closest equivalent pitch. For example, the true 11th harmonic for C lies about halfway between F and F#. This, Hammond felt, was absolutely too great a discrepancy, and thus there is no 11th harmonic on the X66. But having at least the 7th and 9th is a real plus, giving these instruments a host of new and interesting tonalities not found on traditional Hammonds. In my experimentation, I have added (via MIDI) a synthetic 11th harmonic to some MIDI tones and find that I have to agree with Laurens Hammond. The closest available pitch to be an 11th harmonic for some other note is too far off to work if you derive these harmonic pitches from the equally tempered scale. This, however points up another useful aspect of MIDI. It makes it easy to experiment with different tonal effects. You don't have to go and rewire your Hammond organ; MIDI gives you an opportunity to replicate various harmonically synthesized tonalities to find out if including some of these more "exotic" odd-numbered harmonics out of the tempered scale pitches can work. And by my doing this via computer running MIDI software, I have conclusively proven to myself that a fake 11th harmonic does not work out.

In some very elaborate pipe organs, extra mutation ranks of pipes are provided which are correctly tuned to sound the true seventh and on rare occasions, also the true 11th. When done this way, having a true 11th harmonic as well as a true seventh adds immeasurably to the tonal possibilities and is indeeed most useful.