Tone generation

Note: Organs produced after 1968 had a letter prefix code in the serial number: A=1969, B=1970, C=1971, D=1972, E=1973. Sometime in mid-1973, in the mid-200000's, Hammond dropped the prefix letter. Sometime in mid-1973, in the mid-200000's, Hammond dropped the prefix letter. Special Notice: Hammond organ Sales Person Needed in the greater Houston, TX Area. Click here for more information Nice 1969 Hammond B3 with Leslie 122, $12,500.00 $9,500.00 ON SALE! Hammond Age List Entry. Admin Login. MODEL varchar(20). Serial Number varchar(12). Year varchar(6). Confidence Level varchar(6). Owner varchar(80) Contact Info. From serial number 2501 onwards a deeper cabinet was used (that would last with few changes to the B-3)the model was designated AB. Model A-100, A-101, A-102 1959 - 1965.

In imitation of a pipe organ, with its banks of pipes in multiple registers, the Hammond Organ used additive synthesis of waveforms from harmonic series to generate its sounds. As in Thaddeus Cahill's earlier Telharmonium, the individual waveforms were made by mechanical 'tonewheels' which rotated beneath electromagnetic pickups. Although they are generally included in the category of electronic organs, strictly speaking, because the waveforms are produced by mechanical tonewheels rather than electronic oscillators, original Hammond organs are electromechanical rather than electronic organs.

The component waveforms can be mixed in varying ratios by using 'drawbars' mounted above the two keyboards. The drawbars, which operate like the faders on an audio mixing board, allow the performer to vary the volume of each notes' fundamental tone, the octave below it, and the octaves and harmonics above it. Other features added to Hammond organs included an electromechanical vibrato and, by the late 1950s, a reverb effect which simulated the reverberation of a large church hall. The distinctive 'key click' that was originally a design flaw rapidly became part of the 'Hammond sound', which modern imitations of the Hammond organ try to reproduce.

Speakers originally designed by Don Leslie were widely used with the Hammond organs, though at first, Leslie was a competing company that Hammond sought to drive out of business. The Leslie speakers had a rotating horn and a stationary bass speaker with a rotating baffle that produced a vibrato effect. As well, the Leslie speaker cabinets', the valve amplifier gave the Hammond's tone a warm, natural 'overdriven' sound, which could be varied from a mild 'purr' to a heavily overdriven growl. Soon, the Leslie speaker cabinet's signature sound became a de facto requirement for Hammond enthusiasts.

The tonewheel system

The sound reproduction system is based on tonewheels. There are one of these wheels for each of the ninety-one tones the organ can produce. Each key on the keyboard can control up to nine tones, depending on the drawbar settings or drawbar presets. Each tonewheel has a number of bumps along its edge. The number of bumps and the rotation speed of the wheel determines the tone's frequency. A synchronous motor turns the wheels through a set of axles and gears. The gear ratios determine each wheel's rotation speed. The entire gear train rotates continuously. An electromagnetic pickup is placed next to each tone wheel. The bumps in the edge of the tone wheel cause the magnetic field of the pickup to vary, generating a periodic voltage change in the pickup's coil—a tone. The organist selects these tones via the drawbar circuitry and the keyboards while playing the organ. The resulting tones are ultimately amplified and converted to sound by a loudspeaker.

Keyboards and pedalboard

The lightweight construction of the 'waterfall'-style keyboard for the upper manuals allows for very rapid passages to be executed with more ease than on a weighted keyboard, such as a piano or pipe organ.

Most Hammond organs do not have a full, 32-note American Guild of Organists pedalboard going up to a G (3rd leger line of the bass clef) as the top note. Instead, to reduce the cost of the instrument, or the size of the bass pedalboard, 25-note (with a C on the 1st leger line of the bass clef as the top note) or 30-note (with an F on the 2nd leger line of the bass clef as the top note) bass pedalboards are often used. Several Hammond 'concert' models, the RT-2, RT-3 and D-100 had 32-note AGO pedalboards, in addition to a 'Solo Pedal Unit' which provided several 32', 16', 8', 4' voices on the pedal. The solo pedal unit used oscillators, similar to those used in Hammond's 'Solovox'.

The drawbars

The drawbars add harmonics to the original note that each key produces. This is mainly fifths and octaves, and one major third.

Pipe Pitch	Scale interval	Stop name	Note name
16'	Sub-octave	Bourdon	C (octave under root)
5 1/3 '	5th	Quint	G (fifth over root)
8'	Unison	Principal	C (root)
4'	8th	Octave	C (octave over root)
2 2/3'	12th	Nazard	G
2'	15th	Block-flute	C
1 3/5'	17th	Tierce	E
1 1/3'	19th	Largiot	G
1	22nd	Sifflote	C

Types of Hammond organs

The model B-3 was, and still is, the most sought-after model, though the C-3 differs only in cosmetics. Hammonds can be divided into two main groups: the 'Console' models such as the B-3, C-3 or A-100 which have two 61 note manuals and the smaller 'Spinet' models that have two 44 note manuals such as the M-3, L-100 and the M-100. Hammonds' serial numbers are not sequential from one production lot to the next, which can make it difficult to determine the date of manufacture of a Hammond organ.

Not all Hammonds used tonewheels and drawbars; the Hammond company produced a number of cheaper organs which used a simpler electronic way of producing sound, such as the model J100, but these instruments do not have the distinctive Hammond sound. By 1975, synthesizer technology had reached the point where the unique Hammond sound could be fairly closely simulated electronically. However, accurate imitation of the Hammond sound with simple electronic circuitry was difficult, because the subtly-changing ph

Hammond Organ Serial Numbers