X 66

ANIMATION SYSTEM ~ Vibrato and Celeste

Before continuing with the rest of the X66 percussion system, now that you've seen a few pictures, I want to continue the tech description by taking a good look at the X66 vibrato and celeste sections. Most of what I include here is technical fact, however, there are a few comments that I will make that are my opinions and must be considered as such and not necessarily as absolute fact; however these opinions are based upon circumstantial and/or anecdotal evidence and may at least be considered as good possibilities of what was actually true.

We do know from research that Laurens Hammond was, for most of his tenure as company head, opposed to the use of Leslie speakers on his instruments. [Here comes the first opinion.] It seems likely, however, that he could not ignore the multitude of Leslie speakers installed on many Hammond organs, and he also could not ignore that many Hammond distributors stocked Leslie speakers and sold them to Hammond purchasers [in spite of his desires.] And he also could not ignore the number of prominent musicians who were using Leslies with their instruments regardless of what Laurens Hammond felt.

It is, [my opinion] therefore very likely that when Laurens Hammond and his people were developing the X66, he wanted to be able to reproduce the effect of Leslie tremolo (if possible) especially on such an important instrument as the X66; but he wanted to do so without relying on any aspect of Leslie's patented technology. Read about Leslie Tremolo here if you haven't already done so.

It therefore seems likely that he and his various engineers and consultants obtained at least one Leslie speaker and made a careful study of it. I base this opinion on the idea that there are, as we will soon see, many interesting parallels between how the vibrato system of the X66 is designed and works, and what happens in a real Leslie speaker, and perhaps the most significant feature that lends credence to this opinion is that the X66 vibrato as designed sounds a lot like Leslie tremolo, much more than the vibrato of conventional Hammonds, and certainly much moreso than the vibrato of any competing instruments.

In a traditional Hammond organ, there is one vibrato system. It affects the entire instrument when in use, and as the traditional Hammond is a mono instrument, it outputs a mono vibrato signal. A real Leslie, when using the tremolo, produces a stereo signal of effectively an infinite number of channels. A second consideration is that a real Leslie uses a crossover network to separate the applied signal into two frequency bands, one handling everything below 800 Hz, and the other band taking care of everything over 800 Hz. Of course there is not a sudden change over; that is there is some frequency overlap between the two, but perhaps prefacing the statement about the frequency crossover with the word nominally would be more appropriate.

The important consideration of course is that in a real Leslie speaker, the lower frequency tones are handled somewhat differently from the higher frequency tones. In the Hammond X66, all frequencies up to Middle G are processed by one type of vibrato device, and everything from G# all the way to top C are processed by a different vibrato system. So here is the first apparent parallel between the X66 vibrato system and a Leslie speaker, the handling of lower and higher frequencies by different vibrato systems. And we may further add, the effect on the signal roughly parallels electrically what the two different systems in a real Leslie do acoustically.

We will look first at the X66 main vibrato scanner, a picture of it is above, figure nineteen. Normally this scanner is enclosed in a sheet steel box. Here it is with the box removed. Being a high impedance capacitive device, it would otherwise be very susceptible to picking up 60 Hz power hum and other electronic noises. Steel plate provides excellent electromagnetic shielding. It also keeps dust and dirt out. This scanner produces the vibrato for all pitches from Middle G# to the highest C.

We've already discussed the vibrato system of a standard Hammond organ here, so review that if necessary. In that essay, we covered in detail the interesting way in which it roughly parallels electrically what the Leslie tremolo does acoustically to the sound of the instrument. As in a conventional Hammond, the signal to get vibrato is sent to the vibrato line box. In each section of the line box, the phase of the signal is shifted slightly. The vibrato scanner then sequentially picks up signals from different sections of the line box in both forward and reverse direction, creating a slight lowering of the pitch on the forward direction and raising it on the reverse direction.