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So many 'electrical organs' have been experimented with that the musical public may fail to appreciate the possibilities of the Electrone - a new British development in the production of authentic organ tones by means of a comparatively simple arrangement of discs, amplifiers and load speakers. -This article describes how the Electrone obtains its unique sound effects.
Although it is the token of a - musicianly mind to disdain the cinema organ, probably 50% of the musicianly-minded nourish a secret interest in the tricks of tone colour which the modern cinema organ achieves. And nearly all musicians will evince interest in an entirely new electrical development in organ building which was demonstrated to The Wireless World last week by the designer, Mr L E A Bourn, at the works of the John Compton Organ Company, makers of the BBC instrument at Broadcasting House.
The Electrone, to use the tentative name of the new device, is at present restricted to solo purposes on cinema organs for the simple reason, that a full compass of notes has not yet been attempted, but there seems to be no reason why the principles involved should not be embodied in a 'church' organ to the complete exclusion of pipes. By the use of loud speakers, a, valve amplifier and a metal disc revolving at constant speed, the Electrone builds up from pure notes a variety of tone colours which may seem incredible to those who have not heard the instrument demonstrated.
Controllable Reverberation
Inside the 'works' of the. Electrone organ. The tone-generating discs are mounted above the keyboard and 'stop' relays.
In addition to the Tibia, or near-dia-pason tone, which may be regarded as the foundation stop of all cinema organs, the Electrone produces startling imitations of the tones of harpsichord, glockenspiel, cor-anglais, chimes, harp, Hawaiian guitar (with glide effect), saw, vibraphone and other instruments. Effects of resonance can be introduced and controlled to give any required echo effect - an invaluable feature for organs in small rooms, - cinema theatres, and other places which may be regarded as acoustically dead and, moreover, it is possible by the adjustment of capacitors and resistances to obtain a straight line response or any particular building in which the instrument may be installed.
The chief advantage of the Compton system over the majority of earlier methods is that it dispenses with separate valve oscillators, photo-electric cells, etc., for, the development of the tones; Sine waves of various pitches corresponding to the usual range of fundamentals and harmonics in the musical scale are engraved concentrically on a fixed insulating disc. The grooves are filled in with conducting material and contacts are brought out from each ring. A second disc revolving at constant speed and spaced about a millimetre from the first carries an exploring electrode which is connected to the grid of the first valve of a power amplifier of the usual public address type. If a constant DC potential is applied to the sine wave conductors in the fixed disc, an alternating voltage is induced in the revolving electrode, and by charging a group of rings simultaneously by the use of the usual organ stop relays any desired tonal quality can be built up. Not only are the strengths of harmonics adjustable relative to the fundamental, but the fundamental itself can be pre-set to compensate for irregularities in the loud speaker response, so that a perfectly uniform sound level is obtainable throughout the range of the instrument.
The simulation of reverberation effects is obtained by connecting padding capacitors in parallel with the tone generator capacities. High resistances are connected between each ring and earth to dissipate residual charges which might other wise lead to the discovery of unexpected 'lost chords', and the time-constant of the added capacity discharging through these existing resistances gives the required 'die-away'.
Tremolo effects are achieved by mechanically rocking the fixed disc through a small angle, while the gliding tone of the Hawaiian guitar is reproduced by a relay which slows the driving mechanism while the hands are raised from the keyboard and allows it to return gradually to normal as soon as the next note or chord is played.
The Electrone is already being added to a number of organs in the larger cinema theatres in this country, and we imagine that the expression on the faces of some of our amateur organists when they hear a perfect glissando emanating from a keyboard instrument would make an interesting study.
Schematic circuit diagram illustrating the basic principle of the Compton Electrone organ.
Additional Material
The 'Electrone' and 'Melotone' Leslie Bourn, United Kingdom, 1932.
Brochure cover.
Since the 1920's the Compton Organ Co had been the premier manufacturer of pipe organs for cinemas, churches and dance halls in the UK. In 1932 Compton developed their first electronic 'pipe-less' organ the 'Melotone' intended as an add-on unit for conventional organs to extend their range. The Melotone's sound was generated using the same tone-wheel technique as the Hammond Organ and the much earlier Telharmonium (1876), where a metal disc engraved with representations of sound waves spun within a magnetic field generating varying voltage tones. In this case two electrostatic tone wheels provided the sounds, amplified and fed to a large speaker horn in the organ loft. The Melotone was not intended as a complete instrument in itself and had it's own ethereal synthetic character to contrast with a traditional pipe organ.
The Compton Melotone add-on unit.
In 1938 Compton developed the Melotone concept into a stand-alone organ called the Electrone (or Theatrone) designed as a replacement for old pipe organs in churches and dance halls. This instrument had twelve tone generators and an organ-stop style range of voices. A post-war compact 'economical' version was brought out in 1952 also called the 'Melotone'. Production of the organs continued until the 1960bs by which time tone-generator technology had become obsolete due to the arrival of cheaper and more dependable solid-state electronic circuitry.
One of the twelve tone wheels of the Compton Electrone.
The website given below contains links to YouTube videos of the organs.
Source 120 years of electronic music
The history of the Compton Electrone was compiled by John Harvey in 2010 and his article in PDF form is available here.
Compton made about ten different types of rotary electrostatic tone generator, starting with the large type found in cinema-organ Melotone attachments where the entire compass of the instrument is covered by two units. Each pitch is available with one waveform only, and the need to make the waveform ends 'meet up' around the discs prevented the tuning being accurately even-tempered.
By 1938 Compton were producing stand-alone electronic organs, Theatrone (for entertainment) and Electrone (for classical music) which used 5-inch diameter generators. Twelve generators, internally identical but running at different speeds, provide the twelve semitones / pitch classes of each octave. Prewar versions of these generators have two different waveforms available, while in 1947 the design was updated to include four different waveforms each offering between five and eight octaves.
Various developments and elaborations appeared over the next few years with increasing numbers of traces and ranks packed into the same space. These allowed better simulation of pipe organ tones but tended to lower the signal-to-noise ratio of the generator itself and also expose the SNR of the amplifier due to the lower output per trace. It became necessary to insert a muting relay in the audio signal path to silence the instrument when nothing is being played. Such arrangements became quite common on electronic instruments generally, although mainly to eliminate 'bee-hiving' where all pitches are heard simultaneously in the background due to keyer crosstalk. In the Compton it is mainly to combat noise from the generators themselves.
In 1952, Compton launched a new generator that returned to one waveform type, used in conjunction with additive synthesis (like a Hammond organ, and covering the same tonal range and compass). With only seven traces, it was possible to make these half the size at 2.5 inches diameter and use a smaller motor. The new 2.5-inch generator system was compact enough to fit within a standard 2-manual console and offered lower cost and better SNR, at the expense of less subtlety and scope of the pipe tones they could produce. Ultimately, by numbers, most Compton electronics produced in the 1950s and 60s used 2.5-inch generators, which were further updated in 1963 as were the 5-inch types now used in only the very large instruments.
The notes above came from Vintage Radio.
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