TECHNIQUES PAGE
Tone Generation
There are many methods used for tone generation, the most conventional of course being the original ranks of wind driven pipes. From the 1950's through to the 1980's a wide variety of electronic and electromechanical ideas incorporating valves, transistors, neon gas tubes and probably the most famous of all: the Hammond tone wheel generators, were utilised. From the 1980's onwards the most common methods used for tone generation have been digital utilising large scale integration and floppy discs or compact discs (cd ROMs) .
Hammond Tone Wheel Generators
This unique method consists of magnetised wheels that are belt driven. The rotating wheels create oscillations which are picked up and fed into tone forming circuits where the footages can be infinitely mixed with Hammond organs now very familiar and effective drawbar system. Hammond organs using the tone wheel system of tone generation are well sought after nowadays, particularly because the distinct sound produced lends itself well to jazz, soul, and rhythm n' blues. Just listen to the American jazz soul and blues organist Jimmy Smith, and the funky playing style of Georgie fame and you will see what I mean ! Hammond ceased production of tone wheel circuit organs in the mid 1970's due primarily to cost because each tone wheel has to be individually tuned, which is very skilled and very time consuming. They consequently switched to manufacturing Transistorised Frequency Divider circuitry driven by master oscillators.
Master Oscillator / Frequency Dividers
This form of tone generation was and still is the most popular method, It consists of twelve master generators to generate the top octave. Each master generator drives five frequency dividers to generate the notes of the five lower octaves. This system is popular because it is relatively cheap to build, easy to tune and is very stable because the divider circuits lock onto the master oscillators. The main and probably the only drawback is that because all five octaves are locked onto the master oscillators the sound tends to appear "dead", but nevertheless this is overcome by using vibrato circuits and mechanical or electronic tremulants.
All is not lost however ! I have discovered that by adding one or more sets of master oscillator/dividers ( as in adding more ranks of pipes in a pipe organ ) you can really make an organ of the master oscillator generation "come to life". If you refer to my technical page you will find a schematic diagram and some directions to construct a set of master oscillators and dividers to add to your theatre organ which should enhance the sound / performance immensely. This modification is an improvement because added sets of master oscillators beat with and against in an infinite combination creating a resultant sound, which is equal to that of an organ with full independently tuned oscillator circuitry i.e. a separate oscillator for each note on the keyboards.
Independently Tuned Oscillators
Organs using this kind of tone generation when played give what can only be described
as a true, full, rich theatre organ sound. This technique is very expensive to produce
because all sixty one oscillators for each keyboard have to be individually tuned
and also the circuitry has to be exceptionally stable ( there is no lock -
I have explained all of the favourite methods of tone generation, there are many more, but they mostly can only be categorised as either too strange or too impractical. Whilst I cannot indulge in lengthy descriptions of further methods of tone generation here, anyone wishing to contact me is welcome to do so.
Chris Rolph.
Webmaster, Theatre Organ Magic ©
