THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

18.12 Electrical and Electronic Instruments 557Figure 18.38. Schematic of a transistor oscillator network.makes it possible to adjust the output sound level. The sound of the guitar resemblesthat of the conventional instrument.Generating music by electronic means has a history older than most people realize.Early electronic instruments include the Theremin (1919), the Ondes Martenot(1928), the Trautonium (1928), and the Hammond organ (1929). 2 The early meansof electrically generating music were based on the technology that prevailed in therecording and sound reproduction industry of the time. Electronics progressedrapidly during World War II and even more rapidly with the development of transistorsand eventually with the advent of microcircuitry.Because of the rising costs of traditional pipe organs and the desire then prevailingfor creating sustained tones, much attention has been conferred on developingand marketing the electronic organ. Vacuum-tube oscillators and, later on,solid state oscillators were used to generate the tones in an electronic organ. Theschematic of a transistor oscillator network is shown in Figure 18.38. Power fromthe output network is fed back to the input network. Oscillations occur when morepower is developed in the output than is necessary for the loss in the input circuitry,combined with appropriate phase relations between the current and voltages in theinput, feedback, and output networks. Under these conditions, the reactions consistof regular surges of power at a frequency that depends on the constants of theresonant elements in the input or output networks. The resonant elements includequartz, crystal, tuning fork, inductance–capacitance, and so on. These electronicsystems are capable of simulating the wave shape of almost any musical instrument.One type of electrical organ makes use of air-driven reeds and electrostaticpickups. Most of the electronic organs consist of two manual keyboards and a2 An interesting review of these instruments and their history may be found in texts by Rossing (1990)and Strong and Plitnik (1983).