Differences between current version and predecessor to the previous major change of ToneWheel.

Other diffs: Previous Revision, Previous Author

Newer page: version 11 Last edited on May 25, 2016 9:22 pm. by JimCook
Older page: version 9 Last edited on February 6, 2009 9:24 pm. by JimCook
@@ -1,23 +1,23 @@
-Each tonewheel is a disc of soft iron with a diameter of approximately 2 inches. The rim of the disc is "hobbed" or cut with a specific number of smooth, rounded bumps or "teeth". As the disc rotates, this alternation of the radius leads to a modulation of the magnetic field of the MagnetAndCoil pickup. This induces an alternating voltage in the coil of the pickup. There are 96 tonewheels in the generator of most Hammonds, however, some tonewheels are blank and included only to balance the geartrain. 
+Each tonewheel is a disc of soft iron with a diameter of approximately 2 inches. The rim of the disc is "hobbed" or cut with a specific number of smooth, rounded bumps or "teeth". As the disc rotates, this alternation of the radius leads to a modulation of the magnetic field of the [Magnet and Coil| MagnetAndCoil] pickup. This induces an alternating voltage in the coil of the pickup. There are 96 tonewheels in the generator of most Hammonds, however, some tonewheels are blank and included only to balance the geartrain. 
  
-The shape of tonewheel teeth are generally designed to produce a pure sine wave. However, the lowest octave of tonewheels in late model organs do not produce a sine wave. This octave is used only in the pedals. With only two [Drawbars] to control the pedal waveform, the pedal tones in early Hammonds (A, B-1 & B-2, etc.) sounded a bit dull. In the most popular model Hammonds (B-3, C-3, etc.) the tonewheels of this octave are cut with a more complex pattern to improve the sound (See ComplexToneWheels). 
+The shape of tonewheel teeth are generally designed to produce a pure sine wave. However, the lowest octave of tonewheels in late model organs do not produce a sine wave. This octave is used only in the pedals. With only two [Drawbars] to control the pedal waveform, the pedal tones in early Hammonds (A, B-1 & B-2, etc.) sounded a bit dull. In the most popular model Hammonds (B-3, C-3, etc.) the tonewheels of this octave are cut with a more complex pattern to improve the sound (See [Complex Tone Wheels| ComplexToneWheels] ). 
  
-While each output above the first octave of the ToneGenerator should be a pure sine wave, there is some distortion: 
+While each output above the first octave of the [Tone Generator| ToneGenerator] should be a pure sine wave, there is some distortion: 
  
-* The SynchronousMotor pulses slightly as it rotates. Left unaddressed, this would cause a throbbing quality to the sound. Hammond effectively limited this by the use of a resilient CoilSpring between the synchronous motor and the drive shaft to absorb the pulses. 
+* The [Synchronous Motor| SynchronousMotor] pulses or "cogs" slightly as it rotates. Left unaddressed, this would cause a throbbing quality to the sound. Hammond effectively limited this by the use of a resilient [Coil Spring | CoilSpring] coupling between the synchronous motor and the drive shaft to absorb the pulses. 
  
 * Eccentricities in the shape of the tonewheels can create a subtle low frequency amplitude modulation. The frequency of this modulation will be the same as the rotation speed of the tonewheel. Usually this modulation is low enough not to be objectional but if too apparent, the only solution is to replace the offending tonewheel. For a more in-depth discussion of the effect that eccentricities in the shape and mounting of the tonewheels has on the sound, read the [patent|HammondPatents] application for No. 2,314,496. This patent describes a tonewheel generator that apparently was never commercially produced. Start reading about the end of the third page for Hammond's description of how the rotational speed of the tonewheels adds undesirable harmonics and how the "improved" generator disguises these by making them more "vibrato-like". 
  
-* Eccentricities in the gear train can create subtle low frequency amplitude and frequency modulation. It is impossible to precisely machine the DrivingGear''''s and the DrivenGear''''s . Out of round gears, irregularities in the teeth, backlash and the clearances between the teeth can cause these modulation problems. LaurensHammond describes this problem at some length in the original patent (nearly all of page 6 - See HammondPatents). This is why each driving gear is isolated from the drive shaft by a resilient CoilSpring . Eccentricities are dampened but are not completely eliminated by the springs. Like eccentricities in the tonewheel, if the sound is too distorted the only option is to replace the offending gear(s). 
+* Eccentricities in the gear train can create subtle low frequency amplitude and frequency modulation. It is impossible to precisely machine the [Driving Gears| DrivingGear] and the [Driven Gears| DrivenGear] . Out of round gears, irregularities in the teeth, backlash and the clearances between the teeth can cause these modulation problems. [Laurens Hammond| LaurensHammond] describes this problem at some length in the original patent (nearly all of page 6 - See [Hammond Patents| HammondPatents] ). This is why each driving gear is isolated from the drive shaft by a resilient coil spring . Eccentricities are dampened but are not completely eliminated by the springs. Like eccentricities in the tonewheel, if the sound is too distorted the only option is to replace the offending gear(s). 
  
 * Tonewheels can become slightly magnetized. This rare event can happen in organs which have not been operated for a long period of time. If the tonewheel is kept in one position too long, the magnetized pickup slowly magnetizes it. This results in a subtone which is twice the rotating speed of the tonewheel (because every magnet has a north and south pole). Over time, the tonewheel will gradually lose this magentic orientation if operated regularly. However, if this subtone is too objectionable to wait, the tonewheel needs to be demagnetized. This is a job for a skilled Hammond tech since the risk is very high that you could also accidently demagetize the pickup. 
  
-* Some harmonics are produced by magnetic crosstalk HarmonicLeakage from adjacent tonewheels (See CausesOfCrossTalk). Most pickups are fitted with passive filters to limit these harmonics. Many people feel these leakage harmonics are part of the Hammond "sound". However if the leakage is too objectional , the tone generator may need a CapacitorReplacement. 
+* Some harmonics are produced by magnetic crosstalk [Harmonic Leakage| HarmonicLeakage] from adjacent tonewheels (See [Causes of Cross Talk| CausesOfCrossTalk] ). Most pickups are fitted with passive filters to limit these harmonics. Many people feel these leakage harmonics are part of the Hammond "sound". However if the leakage is too objectionable , the tone generator may need a [Capacitor Replacement| CapacitorReplacement]
  
 * Tonewheels can become damaged. The pickups were carefully adjusted at the factory to be a specific distance from the tonewheel. If an attempt is made to adjust a pickup closer to the tonewheel it's possible for the tonewheel to hit the pickup. This is going to cause the soft metal of the tonewheel to become deformed which is going to distort the sound. If the damage is bad enough, the tonewheel could also be out of balance. A tonewheel replacement is the only way to eliminate this distortion. 
  
-* Distortion from the AC mains frequency (See CausesOfHum). The AC mains frequency of 50 or 60Hz is present throughout the organ. To a certain extent you can't do too much about this. However, if a HammondClock or similar mains powered device is set on top of the organ, it can induce a great deal of hum. The solution for this is simple, move the clock. 
+* Distortion from the AC mains frequency (See [Causes of Hum| CausesOfHum] ). The AC mains frequency of 50 or 60Hz is present throughout the organ. To a certain extent you can't do too much about this. However, if a [Hammond Clock| HammondClock] or similar mains powered device is set on top of the organ, it can induce a great deal of hum. The solution for this is simple, move the clock. 
  
 The number of bumps or "teeth" on a tonewheel is 2, 4, 8, 16, 32, 64, 128, and as an exception of the power of 2 series, 192. Each successive change in the number of teeth in octaves 1-6 represents a change of one octave: 
  
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