The Instruments Ken Griffin Played
re-write December 2002)
Eric C. Larson
So well has it become known that almost everybody is at least marginally aware of the Hammond tonewheel organ. Typically, when one thinks of an electronic organ, it is invariably the sound of a tonewheel Hammond or the classic look of a B3 that comes to mind. At least some of this widespread popularity of the Hammond is due to Ken Griffin, whose best selling hit records did much to further the general public's awareness of the Hammond organ.
Then too, the sounds of the Hammond tonewheel organs are distinctive, but they are all very pleasant sounds, and they are musically useful sounds. Also, the traditional tonewheel Hammonds are the closest thing to an indestructible electronic musical instrument ever created. Countless stories exist of Hammonds that have been underwater, gone through burning buildings, been dropped off the tailgates of trucks, and been gigged around all over the country for years, and they continue in most cases to work flawlessly, or require at best just a thorough cleaning and drying out.
Here are pictures of two Hammond consoles of Ken's era [made ca 1949-1954]
Left: Eric's Hammond C2 just like the CV, BV & BCV that Ken used. Right: The CV that Eric plays at his local Skating
Rink. The CV is one of the instruments that Ken played, or it is electrically identical tothe BV and the AV.
The tonewheel Hammonds of Ken's time are very similar to the well-known Hammond B3. Indeed, anyone familiar with the B3 would instantly recognize the Hammond model BCV, and the model AV, both instruments which Ken used frequently. The BCV and the AV have the same general appearance with their familiar, four-legged consoles, the same reverse-color preset keys, the same groups of drawbars, and the round vibrato control knob just above and to the left of the upper manual. It is probably safe to say that many of the internal parts of the BCV and the AV could be used as direct replacements in a B3.
Even at these early stages of the Hammond's development, there were two major different console styles, the A's and B's being the ones with four legs, and the C's and D's having solid sides and backs, designed to have a liturgical look for church usage. In either case, models with similar suffixes are electrically and musically identical; that is, a Hammond CV and a Hammond BV both sound and operate the same and have identical specifications and tonal resources. When a C type console contained a chorus generator, it was called a D, rather than a CC. However, a B type console with a chorus generator was always called a BC. If either of these early models also had vibrato, they were obviously CV's, BV's, BCV's and DV's.
The early AV's are the original Hammond model A's that were equipped with Hammond's pitch-varying vibrato. The BCV's were Hammond's early model BC's, likewise fitted with vibrato and were predecessors of the B2, which, with the addition of Hammond's touch response percussion feature became the famous B3. Indeed, the modern B3 is, relatively speaking, very similar to the BCV, with the exception of more modern electronics and minor wiring changes which are responsible for the Hammond percussion feature and the independently available vibrato on either manual. Other slight wiring differences occur in the manuals themselves, and the shape of the tonewheels for the first twelve pedal tones is slightly different also. One thing, however, that set the BCV apart from the B3 was the inclusion of a chorus generator. This is actually a partial set of additional tonewheels, so arranged that they generate a series of pitches which differ very slightly from those of the main tone generator assembly.
The tonewheel principle upon which these instruments operate is actually a fairly simple application of the basic rule of electromagnetic induction. This rule essentially states that if you have a coil of wire, and you present to it a magnetic field which changes in some manner over time, then, then as long as the magnetic field is changing, a voltage will be induced in the coil. This change can be any kind of change at all. It could be relative motion between the coil and the source of the magnetic field. It could also be caused by the field's changing strength. As long as the magnetic field changes in some manner over time, there will be a voltage induced in the coil of wire.
If the magnetic field gradually becomes stronger or moves closer, current flow will be in one direction. If the field gets weaker or moves away, the current flow will also be in the opposite direction.
The Hammond tonewheel organ contains a series of toothed or lobed steel wheels, roughly two inches in diameter and called tonewheels. Associated with each tonewheel is a bar magnet, about half the size of a normal pencil. One end of the bar magnet is ground to a sharp edge, and it is close to this end that there is a coil of fine wire on each magnet in the instrument. The associated tonewheel rotates very close to the sharp edge of its bar magnet. As the teeth pass the magnet, they disturb the magnetic field that exists at the end of the magnet. There will be a disturbance each time a tooth passes the magnet.
By the above rule of electromagnetic induction, this periodic disturbance of the magnetic field must generate a voltage in the coil of wire. If, for example, a tonewheel rotates at a speed which causes four-hundred forty teeth to pass the tip of the magnet each second, then an alternating current voltage will be induced into the coil, and it will have a frequency of 440 Hertz, or Hz, which is the accepted term for cycles per second. Four hundred forty Hz is of course the pitch of A440, the standard to which all western musical instruments are tuned. As a tooth approaches a magnet, current induced in the coil flows in one direction. As the tooth recedes from the coil, current flow reverses until the next tooth approaches, whereupon the current reverse again to its original direction.
These next three pictures are actual photographs of the interior from a Hammond chorus generator of a model BC. I chose these pictures for three reasons. First, they accurately show the tonewheels, and their associated gearing and the main drive shaft. They also show the special double or two-layer tonewheels that were part of the chorus generator assembly. This article is about the organs that Ken Griffin played, and the BCV was one of those instruments. The Hammonds with chorus generators are rare these days, so where else would you ever get to see one of these interesting variants of Hammond's tonewheel technology? And lastly, I happen to have this chorus generator on a shelf so it's much easier for me to turn it over and photograph its internals that it would be to remove the main tone generator from my working Hammond, which would keep me from playing that instrument for a while, an absolutely intolerable situation for me!
In these special two-ply tonewheel sets, there is one fewer tooth on one ply of the set than on the other. Thus, these double-ply tonewheel sets generate two pitches in the same coil, whose frequencies are very close, but obviously not exactly the same, which is a necessary condition for chorusing as we stated at the "basics" section that preceded the Wurlitzer portion of these articles.
The interior of the main tone generator assembly is very similar, with the only real exceptions being that all of its tonewheels are single ply, and that there are tonewheel sets on both sides of the main drive shaft. These pictures clearly illustrate the drive shaft, the flexible couplings between the sections of the main shaft, and also the unique spring couplings between the pairs of tonewheels and the bakelite gears. It is absolutely imperative that no extraneous gear tooth frequencies or vibrations should affect the smooth rotation of the tonewheels. Therefore, the brass driving gears of the main shaft mesh with the bakelite gears which then transmit the torque to the pairs of tonewheels via the two helical springs on each side.
The bakelite gears are not rigidly coupled to the tonewheels but float on the shafts which bear each pair of tonewheels. If you press gently on the edge of a pair of spinning tonewheels, they will stall, and their bakelite gear will spin freely between the two helical springs. These pictures also show the rod-like magnets and the coils of wire near the magnet tips. Each Hammond tonewheel and its associated magnet and coil constitutes a small AC generator. It is a true generator in that the mechanical energy of the wheel rotation is transformed to electrical energy. This of course is very different from the reed-capacitors of the Wurlitzer that modulate the externally-applied charging DC into an AC signal but do not actually produce any electric power.
In the typical Hammond of this type, the main line shaft turns at exactly 1200 revolutions per minute. Constant speed is absolutely vital for the instrument to be on correct pitch. The 60 Hz power that our utilities supply is extremely accurately controlled. This has been true ever since the large steam-turbine generator units were developed in the early 1900s and power distribution systems began to interconnect in so-called power grids. Utility-supplied power frequency is therefore accurate enough to be considered a constant or an accurate reference standard.
In order to keep the speed of the rotating main shaft at exactly 1200 RPM, which by the way is one exact, complete revolution for every three cycles of incoming 60 cycle AC power, the Hammond organ uses a special type of motor known as a synchronous motor. A synchronous motor runs in exact lock-step with the AC power frequency, so when we say the speed is 1200 RPM, it is 1200, not 1202.47 or 1199.35, but 1200 exactly. This is predicated upon the line frequency being 60 Hz.
The actual synchronous motor of the Hammond organ is known as a reluctance synchronous motor, and as far as we can determine, it was developed by Hammond for his electric clocks. Hammond was an electric clock maker prior to making musical instruments, and the organ was developed several years after the clock business had already been established.
The reluctance synchronous motor of the Hammond organ is considerably bigger than that of a clock, and yet it is also mechanically and electrically one of the very simplest electric motors in existence. However, it has two drawbacks which had to be overcome to make the Hammond organ successful. First, it is not self-starting. It will run forever and drive a load at a precise speed, but only after it has been brought up to speed by some external means. Secondly, it does not spin in an exact, smooth manner, but rather runs in a series of jerks or pulsations, one pulse for each half cycle of the AC power.
The first problem, that of being non-self-starting, is the reason why all of these Hammonds have both a start and a run switch. At the opposite end of the tone generator assembly from the synchronous motor is a small shaded-pole induction motor. Shaded pole induction motors do not have absolutely constant speed, and will slow down slightly with the application of a mechanical load, but they will start by themselves and accelerate to their working speed as soon as we apply power. In the Hammond, the starting motor is designed so that its rotor can slide endwise along the direction of its shaft. There is also a pinion on the shaft of this motor which can mesh with a gear on the main drive shaft of the tone generator.
Normally, a spring holds the rotor and shaft of the starting motor out of position, so that the pinion and gear do not mesh. When Ken would first turn on his Hammond, the power would come to this starting motor, and its rotor would slide endwise as it began to spin. This would engage the pinion with the gear on the main shaft, and the starting motor would bring the shaft and all of the tonewheels gradually up to and slightly above their normal operating speed.
The next thing that Ken would do, as any Hammond player knows, is to turn on the run switch while holding the start switch on. This action applies power to the synchronous motor and also to the organ's electronics. It also puts a resistor in the circuit of the starting motor. The resistor limits the current to the starting motor which reduces its driving power. The synchronous motor starts to take the load, and, since it can only run at exact synchronous speed, it also slows the shaft and the tonewheels down to their correct operating speed. After a few seconds, we can let go of the start switch, which returns to its off position with the help of a spring. The synchronous motor now carries the entire load and turns the drive shaft at exactly 1200 RPM.
The individual pairs of tonewheels in the main Hammond generator run at each of twelve different speeds, determined by the number of teeth on the individual drive gears and the bakelite gears. These twelve speeds are correct for the twelve actual pitches in one octave, that is, C, C#, D, D#, E, F, F#, G, G#, A, A#, and B. The tonewheels of the chorus generator run at 24 different speeds. We will have more to say on the chorus generator shortly.
At this point, we can see that the pitch of a Hammond is directly associated with the 60 Hz. power frequency. We can also see that all of the individual tones of the Hammond are locked into a precise relationship with each other by the gear drives of the tonewheels. Therefore, it is impossible for a Hammond to get out of tune. To be really accurate, we should qualify this by saying that it is physically impossible (barring mechanical damage) for the tones of a Hammond to get out of tune with each other. If the Hammond is used in a location that has an isolated source of AC power and is not connected to a large utility grid, there is a possibility that the 60 Hz power may not be exactly 60 Hz, or that it may vary. In this one instance, the pitch of the entire instrument could deviate from standard. The instrument would still, however, remain correctly in tune with itself, that is, all pitches would have the correct relationship to each other.
Believe it or not, in spite of all the hype about Hammonds never needing tuning, there are very minute tuning inaccuracies in the pitches of certain tones on a Hammond. The factor by which we multiply any tone of the modern equally tempered scale to get the next higher tone is a never-ending decimal. It is roughly 1.06, or when calculated out to thirty-two decimal places, it is 1.05946309435929526456182529494634. (Whew! Glad I have a calculator here.) Now, devising mechanical gearing to replicate this ratio is physically impossible. This is because it is impossible to have gears with a fractional number of teeth.
You can’t make a gear with, say, 56.823467 teeth. The best you could do would be to have a gear with 57 teeth, or possibly one with 56 teeth. However, I mention this as just a point of interest, for the pitches in a Hammond are nevertheless well within the normal standards of tuning accuracy, and each pitch is close enough to be used as a tuning standard for other instruments. Indeed, the Hammond pitches are at least, if not more, accurate than the notes on a correctly tuned piano or most other instruments.
This next picture shows a close-up of the elaborate coupling between the synchronous motor and the main shaft of the Hammond tone generator. Notice that the motor output is connected first through the two coil springs which appear to be at a 45 degree angle to the shaft. These springs connect to a set of double metal discs. These serve as a flywheel. Then notice that the shaft has a large in-line helical spring which connects the flywheels to the coupling on the tone generator. All of this exists to filter the pulsations of the synchronous motor out of the drive so that there is no 120 Hz power ripple introduced into the Hammond tonewheel system. As I already mentioned, additional mechanical filtering comes from the helical springs that couple the bakelite gears to each tonewheel pair.
The Hammond system for creating various different tone colors or timbres depends upon the actual generated tones having absolutely no harmonic content, other than just the fundamental or first harmonic, which is the note itself. In engineering parlance, these tones are sine waves. The Hammond tonewheels are shaped to give a fairly good sinusoidal waveform in the magnet coils. However, stray harmonics do develop. Therefore, each tonewheel above a certain frequency in the middle of the instrument's total pitch range includes a resonant electrical filtering circuit having both a capacitor and a transformer.
We could write several paragraphs about some of the arcane properties of capacitors and transformers under the influence of AC and of the influence of frequency on the properties of both devices, but it is beyond the scope of this article. Suffice it to say that each filter, consisting of a capacitor and also a small transformer, becomes a resonant circuit for one particular frequency. When an alternating current of the correct frequency flows into such a circuit, the circuit resonates or emphasizes that frequency. All other frequencies, both above and below the resonant or pass band of the filter are greatly suppressed.
This next picture, figure 8, shows the top of a main Hammond tone generator with the green felt dust cover lifted up to give you a look at some of the many filter circuits that reside on top of the tone generator cover. In this picture you can see the brown, cylindrical capacitors (rolled up foils in their insulating cases) and also the small transformers. In the foreground, a part of the coils or windings on one of the transformers is visible.
The lower frequencies have less elaborate filtering, as the generated tones tend to be purer right from the coils. Some of the middle notes have transformers only, and on the lowest frequency coils, there are heavy copper rings which help to filter out any traces of higher harmonics in the generated tones.
In the Hammond, there are ninety-one different pitches, representing all of the fundamental and harmonic frequencies that the instrument can produce. Whenever the instrument is turned on, all 91 frequencies will be available and the correct nine pitches necessary for each key will be present on the key contacts for every manual key. On the pedals, the correct eight harmonic pitches will likewise exist on the eight key contacts of each pedal. A little thought on these last two statements will lead you to believe that the same frequencies appear in many different places on a typical Hammond's keys and pedals. This is indeed the case. Obviously, if we have two 61 note keyboards, and each keyboard has nine contacts, this becomes 1098 different contacts, each carrying a single pitch. But we have only 91 different frequencies available. Read on…
The unique Hammond drawbar system is the means that makes it possible for the musician to select which out of the nine available frequencies will sound from any one key. The different tonalities of the Hammond result from a process known as additive harmonic synthesis. The musician can both select or deselect each of the nine available frequencies independently, and also vary their individual volumes, thus giving him the ability to create thousands of different tone colors or musical tones. In effect, the musician determines the harmonic content of the resulting keyboard tones. However, the harmonics of all of the lower tones of the Hammond are also the fundamentals of higher notes. For example, the third harmonic of Middle C on a Hammond is the G an octave plus a fifth above Middle C. This same G pitch is also the second harmonic of Middle G, the fourth Harmonic of the G below Middle C, [Tenor G] the sixth harmonic of Tenor D, and the fundamental or first harmonic for G an octave and a half above Middle C, etc. Every pitch on a Hammond except for the first 12 of the pedals is both a fundamental for itself and some harmonic of one or more lower pitches as well as a sub-harmonic of two additional higher pitches.
Every one of the nine harmonic drawbars of a typical drawbar set on a Hammond can be in nine different positions including "off". Since these nine drawbars can be in nine positions, this gives a total of 387,420,489 different possible combinations. [This is nine to the ninth power.] In actuality, a large percentage of these combinations are either octave duplications of each other, or else similar tonalities but at different volume levels. However, it is safe to say that the Hammond drawbar system does in fact yield hundreds of different-sounding tonal combinations, each of which is capable of a multitude of slight and subtle variations.
Hammond vibrato is one of the truly distinguishing characteristics of all but the very earliest of the Hammond tonewheel console organs. The vibrato, at its maximum setting is full, rich, and adds a great deal of lushness to the sound of the instrument. The Hammond vibrato system is in some ways slightly analogous to the Leslie rotating speaker system in final result, inasmuch as it creates a complex effect that is more than exclusively a simple slight raising and lowering of the instantaneous frequency, however, the basic frequency variation is the major audible aspect of Hammond vibrato.
Like the Wurlitzer electrostatic reed system, the Hammond tonewheel system is not adaptable to variable frequency tone generation. The output frequencies of the tonewheels are constant and can not be directly varied at the source. Therefore, like the Wurlitzer, the Hammond also relies on phase shifting to create a vibrato pitch deviation in the signal after the tones have been generated. In fact, like the Wurlitzer system, the Hammond vibrato takes place in the console preamplification circuits.
Nevertheless, the Hammond organ's means of creating and managing the phase shifts and developing the resulting vibrato are considerably different, more complex, and musically much better than those obtainable from the Wurlitzer system, which just splits the signal into two signals that are 90 degrees out of phase and gates them selectively. From an electronic engineer's standpoint, the Wurlitzer system is superior for its simplicity and lack of moving parts. However, from a musician's view, the Hammond vibrato is vastly superior. And we must of course ask the question here: are we making musical instruments for musicians or electronic engineers?
The distinctive vibrato of all of the tonewheel Hammond organs is produced by two major components that work together; a vibrato line box, and a vibrato scanner. The line box consists of a number of inductance coils of wire, and also capacitors. Each of the many sections of the vibrato line box is actually a low-pass filter, and as the audio signal waves pass through the sections of the vibrato line box, a slight phase shift occurs at each section. The amount of phase shift per section, however is frequency-dependent, increasing as the frequency increases. This exactly parallels the action of a pipe organ vibrato, where the pitch deviation with use of the pipe organ's tremulants increases in the smaller, higher-pitched pipes.
The Wurlitzer system varies the frequency of all tones by the same number of cycles per second. A little thought on this tells us, therefore, that the vibrato effect is more pronounced on lower pitches, because if, for example, the frequency shift at maximum vibrato is, say, four cycles, (approximately correct, actually) then 4 cycles is a 4% shift in frequency for a 100 Hz tone, but only a 0.4% shift for a 1000 Hz tone. The Hammond vibrato, on the other hand, increases the frequency shift with increasing frequency and produces a larger percentage of pitch deviation as we ascend the scale. This is true actually up to the highest C on the Hammond. Above this, the pitch deviation decreases, but the circuit still effectively "scrambles" the phasing and creates a musically useful and pleasing vibrato-like effect. In this instance, the electrical action is analogous to the acoustic action of the rotary treble horn in a Leslie speaker.
The audio signal which is to get vibrato enters one end of the vibrato line box, and each section of the line box creates a frequency-dependent phase shift. The vibrato scanner looks at the vibrato line from one end to the other and picks up signals in succession from the various outputs or "taps" on the vibrato line. The scanner is a rotary device and its internal pickup turns at 412 RPM. For its first half revolution, the scanner picks up signals which are progressively retarded in phase as it scans the line from beginning to end. Then, as the scanner rotates through the second half revolution, it picks up from the end of the line box back to the beginning, now receiving signals successively advanced in phase.
As we now know, a continual phase shift amounts to a shift in frequency, therefore the continuous train of signals that the scanner picks up appears as a replica of the input signal, but its pitch changes constantly, varying slightly above and slightly below the input frequency. Since the pitch deviations are equal and opposite, there is no net frequency change, and the average frequency of the signal from the scanner is the same as that which entered the vibrato system. However, the instantaneous frequency of the scanner output varies both above and below the input frequency and does so at the scanning rate. The scanning rate remains constant as the scanner is gear-driven from a pinion on the shaft of the synchronous motor that drives the tonewheels.
The above operation gives the maximum vibrato, called V3 on the decal of the vibrato control. If the musician prefers a less intense vibrato, he can select positions V2 or V1, which switch roughly 60% and 30% of the vibrato line into service, resulting in a lower aggregate phase change and a smaller pitch deviation for each half-revolution of the vibrato scanner.
The vibrato scanner is, believe it or not, a rotary, sixteen pole variable capacitor. The signals from the taps of the vibrato line box appear on the stationary plates of this rotary capacitor [scanner]. Since the action of AC in a capacitive circuit is such that it effectively flows through the capacitor, (really doesn't, but acts as though it did!) then the signal appears on the rotary pickup of the scanner, to continue on through to the rest of the amplifier. The scanner pickup consists of small brass plates that mesh with the stationary sets of small brass plates all around the periphery of the scanner. Figures nine and ten show respectively a Hammond vibrato line box of one type and also a look at the exterior of a vibrato scanner, where you will see it attached to the synchronous motor.
A third component completes the vibrato system, and that is the vibrato selection switch. Turning the vibrato selection knob effectively changes the wiring connections between the line box and the scanner so that the musician can obtain the three different intensities of vibrato. In spite of the rather simple appearance of the vibrato knob, the vibrato switch is quite a complex device. Immediately below the vibrato knob is a very steep-pitched pair of meshing worm gears which function as a right angle drive. This in turn rotates a camshaft which operates three groups of eight on-off switches, all packed into the relatively small space under the drawbars and just over the upper manual key channels. These switches change the connections from the vibrato line box to the scanner, and determine what percentage of the vibrato line box will be in use at any moment, thus giving the three different degrees of vibrato.
As previously stated, in all natural musical situations, as for example a chorus of singers or an orchestra, it is physically impossible for everyone to be at exactly the same pitch even if all sing or play the same note. This ensemble or chorus effect gives animation and a lifelike and spacious quality to the music. As such, we generally are not even aware of it, because it is present in virtually all music. However, in the case of a Hammond organ, all frequencies come from tonewheels which are gear driven, and thus they are locked into a precise relationship to each other. Furthermore, since there is only one tone source for each frequency on the Hammond, no matter how you register the instrument, there is no ensemble effect as such. This lack of true ensemble is further compounded since all of the harmonics of the different Hammond tones are themselves the fundamental frequencies of the instrument's higher pitches.
Very early in the development of the Hammond organ, the makers realized this shortcoming. The previously-mentioned chorus generator, then, was developed to supply extra, very slightly out-of-tune frequencies to the upper end of the Hammond's pitch range, from the G an octave and a half above middle C to the top of its range. This roughly parallels a natural musical setting in which several instruments play together, but are nevertheless very slightly out of tune with each other because there is no means of synchronization. For example, there is no known way that you can exactly synchronize the pitches of two singers' voices, or the three strings-per-note of a piano, or the different instruments of an orchestra, or the reed-capacitors of the Wurlitzer ES organ, or the independent pipes of a real organ.
The BCV and also the DV had an extra drawbar, located at the upper right end of the instrument, above the start and run switches. Pulling this drawbar out operated a multi-contact switch that connected the outputs of the chorus generator to the output terminals of the main Hammond generator.
After they developed their pitch-varying vibrato, however, someone at Hammond realized that since the vibrato signal is constantly changing its instantaneous frequency, why not mix the straight signal from the tone generator with the vibrato signal? Then an ensemble effect should develop between the two, due to the pitch differences that occur during each positive and negative excursion of the vibrato signal frequency. This they did, and shortly after that, did away with the expense and complication of adding extra tonewheels.
At this point, I will interject my personal opinion on this matter, stating that the chorus effect which resulted from the extra tonewheels was [musically] far superior to the compromise chorus obtained by mixing vibrato and straight signals.
The very first Hammond organs did not have vibrato. Instead they had a tremulant, which simply varied the instantaneous volume of the sound. The tremulant did not sound very exciting at all; indeed it was almost useless. No doubt, this lack of tonal "excitement" was one of the reasons behind the development of the chorus generator. When Hammond developed their famous vibrato, the importance of the separate chorus generator decreased significantly in the opinions of the Hammond management at that period of the instrument's history.
The model BCV and also the DV Hammonds, however, had both Hammond vibrato and the corresponding vibrato chorus as well as the extra set of tonewheels. The effect of V2 or V3 with the true chorus of the extra tonewheels is a very pleasant and musically useful effect. Fortunately, with modern digital signal processing, we can once again simulate this effect quite accurately in those Hammonds which do not have extra tonewheels.
You can hear Ken use this effect in a number of selections, including, That Tumble Down Shack in Athlone, When I Lost You, The Woman in the Shoe, and The Song is Ended.
In these early BCV Hammonds, the vibrato chorus was not a part of the rotary vibrato control as it is on the B3. The BCV did not have C1, C2, and C3 as does a B3 Hammond. Instead, there was a toggle switch on the woodwork that supported the music rack. The vibrato knob had positions V1, V2, and V3 as does a modern Hammond B3, but the positions between these three vibrato settings were simply labeled "off". To get Hammond vibrato chorus, you would set the vibrato knob to one of the 3 vibrato settings, and then flip the toggle switch to the chorus position. If you wanted the true chorus from the auxiliary tonewheels, then you'd pull out the chorus drawbar. Some interesting effects could be obtained by using both choruses together, an effect which is not possible on a newer Hammond. In The Sheik of Araby, you will hear Ken use the Hammond vibrato chorus exclusively.
On the early AV Hammonds, the toggle switch for the vibrato chorus effect was mounted directly on the vibrato line box itself. Interestingly enough, on these early models, the vibrato line box was too big to fit inside the console and was instead placed on the underside of the console shelf. Turning the chorus on and off on these instruments was therefore quite inconvenient. This lead, no doubt, to the placement of the chorus switch on the music rack's supporting woodwork. When Hammond developed the selective vibrato that appeared on the suffix "2" consoles, they placed the chorus on-off switch inside the multi-contact vibrato selection switch and changed the decal to read C1, C2, and C3 along with V1, V2, and V3.
These very early vibrato line boxes were about twice the size of the later line box in figure nine. As Hammond continued to refine the tonewheel models, they shrunk the vibrato line box yet again, to the type which we find in modern B3's. These new line boxes eliminated the wood box entirely, and had a metal mounting bracket at each end.
There theoretically should not be, but there are, nevertheless, very subtle differences between the vibrato effects from the early big wooden line boxes and those obtained with the later type. Some very experienced Hammond players have stated a preference for the sound of the vibrato on the older Hammonds. It is indeed possible, by making a direct, side-by-side comparison of a very old Hammond and a newer B3 to hear the difference in the vibrato effect, particularly on the V3 setting.
Because vibrato is a pitch effect, it will actually sound different in every different room or hall where the instrument is used, and indeed you can pick up slight differences in the vibrato just by moving around in a given room while listening to a note held down. These differences, of course, are caused by the reflected sound waves from the walls, floors and ceilings of these various listening environments. Similarly, the presence of natural reverberation or the application of artificial spring reverb or tape echo to the instrument likewise causes subtle changes in the vibrato, as does the use of multiple tone cabinets.
During World War II, Hammond for a while compromised their pedals by eliminating the first nine tonewheels and magnets. Therefore, even though the pedals extended down to low CCC, the lowest actually generated pitch was AA. The first nine pedal tones were created artificially by combining two existing higher tones whose frequencies were in a 2:3 ratio. For example, by combining the second CC with the next higher GG, a pseudo or resultant frequency having the pitch of low CCC would appear. While not having the depth of a true, generated tone, this did give an acceptable low tone to the first nine pedals. On some of Ken's recordings, if the pedal notes appear to lack the real depth and fullness that are present in other selections, that is the reason. After the war, Hammond resumed their use of a tonewheel for every single pitch on the organ.
Other Hammond instruments which Ken most likely used are the BV, and the CV. There is no real way of identifying by listening what particular model Hammond Ken used on a particular record, other than that we can readily identify the instruments where he used the chorus generator as being either a BCV or a DV. Likewise, we can identify those instruments with a fake 16' pedal by their lack of true depth in the lower pedal tones, but beyond that, it is impossible to know the exact models he used. Individual Hammonds also have a tonal fingerprint as do the Wurlitzer electrostatic instruments, but the differences are extremely subtle and slight and would require extensive analysis with more equipment than is available to me at this time in order to know, for example, if each song on a particular record was played on the same instrument.
Although there are many more aspects to the Hammond organ besides what I have just mentioned, there is such a wealth of material on the Internet about the Hammond that I would refer you to that resource if you want to find out more, including looking at illustrations of the Hammond tonewheels and other components. Just type in "Hammond Organ" or "Hammond Organs" and you will discover hundreds of sites devoted to that instrument.
In a large measure, aside from Ken's musical ability and supremely accurate keyboard and pedal techniques, these two classes of instrument, the 1950's Hammond tonewheel organs and the electrostatic Wurlitzers, are principally responsible for Ken's distinctive sounds. While all of the effects of the early AV, BV, BCV, DV and CV Hammonds, with the exception of the double-generator chorus of the BCV and DV are available from a modern tonewheel B3, C3, RT3 or A100 Hammond, the unusual and sometimes somewhat plaintive tones of the electrostatic Wurlitzer are for the most part not available on any other instrument. At some period, which I believe to be in the year 1961, Wurlitzer abandoned the electrostatic principal and changed over to more modern technology, producing electronic organs similar to those of many other builders of that time period.
It is my hope that this understanding of Ken Griffin's instruments will help in the appreciation of his music. It is a well-known fact that the both the sound and the response of a musical instrument greatly influence the musician's final musical output, and understanding the instruments upon which Ken Griffin played and recorded helps us to know and appreciate his music better.
Eric C. Larson.
Bill Reid – recordings of Ken Griffin's playing taken from his collection of Griffin records for the purpose of analyzing the instruments.
The late C. Robert Montgomery – Hammond technical manuals and a Hammond RT 2 console instrument.
Andrew Jarosik - service manual and general technical info on the Wurlitzer electrostatic organ.