North Suburban HAMMOND ORGAN Society

As you can see by the information on the preceding pages, there is quite a bit to the vibrato on the X66. On many competing instruments of that time, the manufacturers would provide a set of flute-like tones, often essentially sine waves like the tones from Hammond's drawbars and likewise at different pitch levels, and these would be sent through a small Leslie speaker built into the console. The remaining tones which were complex waveforms and had to be formanted to sound like real instruments, did not go through the Leslie. On most of these instruments, it was very easy to add a simple vibrato, because the electronic tone generators in these instruments could easily have their output frequencies varied slightly.

Part of the reason for using these much more elaborate vibrato systems in Hammond organs is that they all relied on rotating tone wheels for either direct tone generation, or reference tone generation, and it was not practically possible to vary the speed of the tone wheels, which meant then that the generated tones would have absolutely steady pitch. All of these various systems that I have just described are designed to vary the frequencies of steady tones, and after-the-fact frequency changing is much more complicated to do.

The nice thing about this elaborate vibrato system in the X66 is that it treats different types of tones differently and also in the case of the drawbar voice vibrato, separates it into two different pitch ranges. The final result is that the X66 produces a vibrato for the drawbar voices that sounds remarkably like that generated by a Leslie speaker, and the vibrato for the formanted voices sounds very much like the effect that the tremulant of a pipe organ creates in the tones of those pipes that imitate reed and string instruments, where the pitch deviation is much smaller, but where there is also a degree of amplitude variation. A further benefit is that the two vibrato scanners in an X66 do not run at exactly the same speed, and the saturable reactor bass drawbars vibrato system likewise is not synchronized to the other two vibratos.

In a real pipe organ, for example, there are usually several different tremulant devices, each handling a portion of the total instrument, and these tremulants likewise are not synchronized and never run at exactly the same speed. In a real orchestra, where each musician is responsible for producing his own vibrato, whether playing a horn, a woodwind, a brass, or even singing, likewise all of these vibratos will occur at slightly different rates. Traditional Hammond organs had just one vibrato linebox and scanner and it affected the entire instrument the same, although the vibrato effect became more pronounced as you played higher tones which of course is a desirable feature. In these traditional Hammonds, the scanners were driven by a reduction gear from the main shaft which was powered by a synchronous motor and always turned at exactly 1200 RPM. The scanners likewise always ran at 412 RPM.

So if you played two or more such instruments together, all of them had exactly the same speed of vibrato. In the X66, the two vibrato scanners are driven by an induction motor via a belt and pulleys; therefore the vibratos in two X66s are not synchronized and will never run exactly at the same rate. Furthermore, the reactor vibrato for the lower drawbar tones is likewise not synchronized to anything else.

The celeste scanner in the X66 is also powered by the same induction motor by the belt which contacts its pulley along with the pulleys of the other scanners. In a sense, it's a little like the fan belts in newer cars where the belt is run over and under several pulleys to operate the alternator, the water pump, an air pump, the power steering pump and the AC compressor.

The important point is that when you have several different types of tones in use simultaneously on an X66, you get a very "big" and lush sound that delivers a much more realistic effect than what is obtainable on other instruments. Another really nice feature also is that, because the Hammond vibrato is electrically produced and applied to the signals while they are still electrical signals, and not applied to the tones after they become sound waves as is the case with a Leslie speaker, you can use many additional speakers on an X66 if you want to fill a big hall with sound, and they can be any ordinary speakers that will handle the power and the frequency range adequately. Also, you can also record directly from the instrument's preamps without resorting to microphones. On those electronic organs which rely on the Leslie speaker for all or a part of their vibrato production, all additional speakers must likewise be Leslies, and recording can only be done via microphones.

As a point of interest, the typical vibrato rates in an X66 are as follows: Treble drawbars vibrato (dual scanner) = 360 vibrato cycles per minute. Bass vibrato (saturable reactors) = 330 per minute; formant and bass pedal vibrato (conventional scanner) = 390 per minute, and celeste effect (dual scanner, geared down) = 40 celesting events per minute.

These rates are approximate, are not synchronized to anything else, and will vary slightly from one instrument to another.


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