• The Electronic Keyboard
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The Electronic Keyboard (Part 1)

Part 1 looks at early keyboard instruments

An historical and technical survey of the development of the electronic keyboard from its origins to the present day. This informative series will be of interest to anyone who has played an electronic keyboard instrument, whether an organ, electric piano or synthesiser, and its practical examples give the electro-music engineer a valuable insight into early music technology.

No one knows when man first discovered he could make pleasing sounds by blowing into a thin tube. Certainly an assembly of such pipes was in use by 900 AD. Pythagoras was the first investigator to suggest an orderly succession of notes, which he found to be 'eight' before he arrived at the original note but one octave higher - hence the derivation of the word octave. By the year 1000, organs with several sets of pipes were in use, even though at this time there was no concept of harmony - all notes sounding in unison. As in many other walks of life, steady improvements in control and tonal quality came from the monasteries. By 1600, quite modern organs were in use, but as they became larger, so it was harder physically to play them; organists were known as 'organ beaters', the clenched fist being used to strike the keys!

19th Century Onwards

Inventors have always thought far ahead of the means to realise their inventions, so it was not until the early 19th century that electricity was applied to ease the touch - although pneumatic assistance was much older. From this period, advances were rapid and by 1851, the year of the Great Exhibition, extremely modern, organs were shown with all pipework used today incorporated.

Figure 1. Hartley oscillator.

But a new line of research was opening up, for in 1837 C.E.J. Delezenne in France produced musical sounds by rotating a toothed iron wheel in front of an electromagnet. The American Thaddeus Cahill soon followed with the Telharmonium, an ingenious if massive series of alternators each delivering a sine wave at the intervals of the tempered musical scale. The output was hundreds of watts, but losses in the controls and the very crude telephone receivers employed consumed much of the power. Following on the work of Fourier and Helmholz, attempts were made to synthesise complex sounds (e.g. clarinet) by mixing sines in a transformer. This bold concept was doomed to failure, but all who heard it commented on the purity of tone - no one had ever heard a sine wave before!

The valve organ

Figure 2. Bistable frequency divider (or flip-flop).

Although Duddell did produce controllable sounds from his 'singing arc', it was the invention of the grid in the valve by de Forest in 1907 that really started the ball rolling. Yet it was only in terms of radio that everyone was thinking and consequently this resulted in circuits of vital importance to the electronic organ being completely overlooked. For example, the Hartley oscillator of 1917; Abrahams & Bloch's multivibrator of 1918; and the Eccles-Jordan frequency divider of 1919. One must allow for economic recovery after the 1914-18 war, but in fact there was a hiatus in organ development then; new valves, gas tubes, better capacitors and resistors, etc. were, in fact all due to the war efforts. The device which was to notably make all organs acceptable then and now was the invention of the free cone moving coil loudspeaker by Rice and Kellog in 1925. It is true that Wehner von Siemens invented a moving coil speaker in 1878, Sir Oliver Lodge also patented one in 1879 and the Magnavox company had one on the market in 1910; but all of these were for telegraph reception and used horns that had stiff diaphragms with no frequency response over any significant range.

Figure 3. A Theremin circuit, with control obtained by body proximity to either or both rods.

Although some attempts were made to foster simple musical instruments like the Theremin, it was left to the French organ builder Coupleux and Giveletto launch a full-scale valve instrument in 1927. At the same time Oskar Vierling produced a quite reasonable organ using gas tubes as relaxation oscillators in 1927-28. The process of tone forming was not then understood but during this period Maurice Martenot was at work in France on several attributes of the organ not so far used. Although he never built a full size organ, he was responsible for introducing vibrato, touch-sensitive keys, and a means of producing gliding tones from a keyboard.

Electro-Mechanical organs

Figure 4. Rotating masks in front of photoelectric cells.

It may surprise some readers to learn that the photo-electric cell was invented in the early 1800's. Several attempts were made to rotate or move masks or stencils in front of such cells to produce musical sounds, but mechanical problems always defeated investigators until the Welte organ of 1928. However, we are running ahead too fast, for it was only too evident to all these experimenters that all the components used were basically unstable, meaning that organs would not stay in tune. By this time, of course, electric motors and general mechanical details were quite refined, so attention was given to electro-mechanical organ generators. The first successful design was that of Leslie Bourne, assigned to the John Compton organ company in 1932. A series of 12 stationary discs, each engraved with waveforms in octave relationship (i.e. a disc would carry all the C's of various tone qualities) was scanned by a spider-like array of pickup elements driven by an endless belt through pulleys, so proportioned as to give the intervals of the tempered scale. By applying a DC potential to the stators, this induced a charge on the scanners proportional to the area scanned; since this consisted of waveform tracks, the charge represented the changes in waveform. A valuable feature of Bourne's system was that since only DC was keyed, RC delay networks could be introduced to eliminate clicks, the bane of all early electronic organs. Since this organ was made in the same factory as the company's pipe organs, a good measure of tonal fidelity was obtained; indeed, the first 'electrones' as they were called, were fitted to Compton theatre pipe organs.

Figure 5. Compton generator, with stator on left and rotor on right.

The popular Hammond

Figure 6a. Hammond tone wheel system.

Meanwhile an American maker of alarm clocks was working on an up-dated version of Cahill's system, and by now there were good amplifiers and indirectly-heated valves; Western Electric had been using thoriated tungsten filaments since 1915.

Thus the Hammond organ made its appearance in 1934 - two years after Bourne. At one time this was the best known organ in the world and certainly the most reliable. The method is well known; small soft iron discs having a contoured edge are driven by trains of gears in front of permanent magnets, each bearing a pickup coil. The voltage induced in these coils is keyed, controlled in volume level by drawbars, mixed in transformer (or resistor) networks and amplified. The system relied entirely on the very ingenious gear drive. The iron discs idle on their spindle, to which is fixed (in the centre) a bakelite gearwheel. On either side of this wheel are compression springs having ground ends. These press on a disc each side and the gear wheel in the centre. Sufficient power is transmitted through the springs to drive the discs, but any small ripple due to the gear wheels is absorbed by the springs; which also allow the discs to slip should a particle of dirt become wedged between the magnet tip and the edge of the disc.

The waveform is not quite sinusoidal and this is largely corrected by filters on each pickup coil; the tuning is permanent but not quite exact between semitones, since it is impossible to generate the true intervals with only two gearwheels. The attack on keying is very abrupt as all the wheels run continuously and, whilst the original concept of this organ was for the church, it was soon found to be admirable for rhythmic playing!

Figure 6b. Hammond chisel-shaped permanent magnet pickup.

Vibrating reed organ

The success of these electro-mechanical organs stimulated others, the most important of which was the vibrating reed organ of Hoschke. Many years of manufacture in the U.S.A. had brought the acoustic reed organ to a high pitch of mechanical excellence. Hoschke polarised the reed bases and placed pickup screws above selected portions of the reed tongues. So long as the wind pressure (really suction) was constant, the screws could not touch the tongues; a charge was therefore induced in the screw, easily converted to an audio signal. Hoschke sold his patents to the Everitt Piano company and many examples of the Everitt Orgatron reached these shores - some are still playing. Later Everitt sold out to Wurlitzer who made a remarkably fine job in developing this type of instrument.

So you can see that here we have three organs, all keeping in tune, all reliable, and all capable of voicing to produce acceptable imitations of pipe organ sounds. Every other system or method failed commercially because of component instability; there was no competition until after the Second World War.


Read the next part in this series:
The Electronic Keyboard (Part 2)

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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Mar 1983


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Vintage Instruments


The Electronic Keyboard

Part 1 | Part 2 | Part 3 | Part 4

Feature by Alan Douglas

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