The US Patent for the Theremin (Page 2 of 3)

The connection of the control-element to the oscillating system may be modified variously while still obtaining the desired result. A plurality of electrodes may be employed to produce plurality of sound tones simultaneously from the same object moved in relation thereto. For example, two straight parallel conductors may be employed. If the object moved relatively thereto is equidistant from both conductors, the two tones produced therethrough will be the same if other conditions are equal. As the moving object approaches nearer to one conductor than the other, the pitch of one tone will increase while that of the other will decrease. Three or more conductors may be provided, preferably in symmetrical arrangement or a plurality of symmetrical groups of conductors may be arranged and controlled by different objects or fingers of the operators hand.

Connection of the conductor or conductors to the oscillator should be such that the changes in capacity will produce a considerable change in the oscillator. Connection may be made either to the grid or anode circuit of the oscillator, the most suitable connections being illustrated in the drawings.

In Fig. 4 a connection of the control element to the anode circuit is shown. With the controllable oscillator 73 is associated an oscillating circuit including inductances 74 and 75 and condensers 76and 77. Energy is supplied to the oscillator by an anode battery indicated diagrammatically at 78. The control element 79 may be connected with the plate circuit as shown in full lines at 79 or with the grid circuit as shown in dotted lines at 79. It makes little difference whether the control element is connected the one way or the other provided conditions are otherwise equal. But if this is not the case. the control element is connected preferably to the larger inductance. The sensitiveness of the system may be increased by grounding the circuit at 80, but as a rule this connection is not required in view of the large counterpoises of the oscillating circuit.

In the system illustrated in Fig. 5. the control element 81 is inductively coupled with the oscillator 83 through the medium of coil 82. An adjustable condenser 84, is shown arranged in the oscillating circuit of the oscillator 83 by which the control circuit is tuned. In this system by reason of the coupling coil 82, the control element may be at a somewhat greater distance from the oscillator 83.

In order to produce a plurality of sound or musical tones simultaneously a plurality of interfering oscillators may be employed. For instance, three oscillators properly arranged will produce two tones, one resulting from interference between the first and second oscillators and the other resulting from interference between the second and third oscillators. In like manner, three tones may be produced by four oscillators and so on.

In Fig. 6 is represented an arrangement for producing two sound tones simultaneously by the use of three oscillators, each tone being separately controllable. One control electrode 35, is shown associated with an oscillator 36 and with a low frequency detector tube 37. Another control electrode 38, is shown associated with an oscillator 39 and a low frequency detector tube 40. The said detectors 37 and 40 are both responsive to the fixed oscillator 41. An amplifier 42 responsive to both of the beat notes or tones is shown connected through a transformer 43 with a sound reproducer 44.

Fig. 7 illustrates a further modification comprising four control electrodes, viz. 45, 45', 45" and 45"' respectively associated with oscillators 46, 47, 48 and 49, whereby four tones may be produced simultaneously. The four oscillators co-operate with a fixed oscillator 50 and are inductively connected with detectors 56, 57, 58 and 59 through coils 51, 52, 53 and 54. Each is also connected with one of the coils 60, 61, 62 and 63 of a transformer. Condensers 64, 65, 66 and 67 are connected in parallel with said coils 60, 61, 62 and 63.The neutral points of all four coils are connected with the coupling coil 55 of a fixed oscillator 50. A secondary coil 68 of the transformer is connected to the amplifier 69 which operates the reproducer 71 through the transformer 70.

Fig. 8 shows another four-tone system but in this instance the high frequency alternating potential is supplied directly from the plate circuit. The coupling coils 51, 52, 53, 54 and 55 are eliminated and replaced by a variable coupling coil 72 which is shown connected to the anode of the fixed oscillator 50 at one end and to the neutral point of the four transformer coils 60, 61, 62 and 63 at the other end. The secondary winding of the transformer controls the amplifier 69 from which the combined tones are transmitted to the reproducer 71 through the transformer 70.

The detectors used in connection with the above systems may be of any suitable type, crystal detectors being considered generally preferable.

For regulating the volume of the sound the intensity of the current may he varied and variation of the current intensity may be effected in several ways.

Referring now to Fig. 9 a connection is shown in which the oscillator or amplifier 85 which generates the sound tones actuates the reproducer 86 to which an adjustable resistance 87 is connected in parallel. The resistance 87 is adjusted by means of a pedal or the like, and controls the volume of the sound. The adjustable resistance 87 may also be connected in series with the reproducer.

Fig. 10 shows a further modification in which an adjustable resistance 88 for controlling the volume varies the cathode current of the amplifier 89, which in turn controls the reproducer 90.

The system illustrated by the diagram of Fig. 11 is similar to that shown in Fig. 10, except that the cathode current is regulated inductively from the high frequency circuit of the tube 100 in the amplifier with utilization of a greater or lesser energy absorption in the conductor 92 as determined by its resonance with the oscillating circuit 91 variable according to the operators movement of his fingers or other object with relation to the conductor.

The conductor 92 is connected with a coupling coil 93, which latter is inductively related to a coupling coil 94 connected in series with the coupling coil 95 for the oscillating circuit 91, and a coupling coil 96 for the cathode of the direct current amplifier. Both coupling coils 94 and 95 co-operate so that maximum energy will be generated when the control circuit and oscillator circuits are in resonance.

The conductor 92 is a separate control element for regulating the sound-volume and will be referred to as the “sound-volume” control element or electrode. Adjustment may be so effected that resonance occurs when the controlling object is either nearest to or altogether removed from this electrode. Therefore, while one hand of the operator generates the various sound tones in the first or “sound-generating” electrode his other hand may regulate the intensity of the tone at the second or “sound-volume” electrode.

The system in Fig. 11 is intended to be connected with the left-hand end of the diagram of Fig. 2, the line III-III in Fig. 11 indicating its point of connection with Fig. 2 The amplifier 98 which is also a direct current amplifier controls the reproducer 99.

The system shown by the diagrams of Figs. 12, 12and 14 are similar to that shown in Fig. 11.

In Fig. 12 the cathode current for the amplifier 97 is generated by direct connection of the transformer 96, with the oscillating circuit 91.

In Fig. 13 the resonance transmission of energy to the circuit 102 through the circuit 101 is utilised under the influence of the controlling object or its distance from the “sound-volume” control electrode.

The “sound-volume” control electrode 92 is directly connected to the anode of the circuit l0l of the oscillator 100 and the circuit 102 which is coupled therewith supplies current to the cathode of the amplifier 97 over the variable transformer 103.

In Fig. 14, the sound volume is related by varying the average grid potential in one of the amplifiers by means of the non-inductive resistance 104, which is also in the anode circuit of the oscillator 98. The circuit of the “sound volume” electrode 92 is coupled with the oscillating circuit of the tube 100, which is connected with the non-inductive resistance 104. If a finger or other object is made to approach the electrode 92 the resonant frequencies of the electrode circuit and of the oscillating circuit of the tube 100 will vary whereby a corresponding voltage drop will be produced in the resistance 104 which by connecting the tube 98 causes a change in the volume of the sound.

The diagrams of Figs. 9 and 14 are most efficient under normal conditions.

The preferred means for switching the sound tones on and off comprise means for controlling the current serving for producing tones in the reproducer.

Fig. 15 shows an ordinary switch, 105, in the plate circuit of the amplifier in series with the reproducer 106, as shown in full lines, or in parallel as shown at 105 in dotted lines.

As shown in Fig. 16 the primary winding of a transformer 107 may be connected in the plate circuit of the amplifier and the tone producer 108 and the switch 109 connected in the secondary circuit of the transformer. This eliminates the undesirable constant component of the pulsating current through the reproducer.

The diagram of Fig. 17 is similar to that of Fig. 16 but the transformer 107 is replaced by a choke coil 110 from which a circuit is branched in parallel, the reproducer 111 the switch 112 and the condenser 113 being connected in series in this circuit.

In Figs. 18a and 18b, the switch is in the cathode circuit. In Fig. 18 the switch 114 controls the current from the filament battery 115 of an amplifier 116, in the plate circuit of which the reproducer 117 is arranged. In Fig. 18b the switch 119 is in a shunt circuit 118 of the cathode heating circuit which is connected with the filament battery, said battery being in continuous connection with the filament wire in series with a resistance 121

In Fig. 19 is illustrated an arrangement for switching the tone on and off by a control analogous to the arrangements for varying the volume of sound shown in Figs. 11 to 14.

The system of Fig. 19 is intended to be connected with the system of Fig. 2 along the line III-III as in the arrangement of Fig 11. The two direct-current amplifiers 97 and 98 control the reproducer 99. A third control-element 122 is provided for switching the tones on and off through the medium of the cathode current, and is operated like the sound generating and “sound volume” electrodes. The control element 122 is coupled with a control circuit coil 123, which circuit includes coupling coils 124, 125 and 126. The coil 125 coupled with the amplifier corresponding with the tube 100 in Fig. 11 and the coil 126 is coupled with the cathode current of the amplifier 127. Current from the anode battery 129 flows through a relay 128 which operates a switch 130. The switch controls the circuit of the cathode battery 131 for the heater of the direct current amplifier 97. By the operators movement of his hand or other object with relation to the electrode 122, the filament current of the amplifier 97 and consequently the tone is cut on or off.

The systems of Figs. 16 and 17 are considered superior to that of Fig. 15, while the systems of Figs. 18 and 19 are regarded as preferable because the switching on and off will take place without any noticeable interval.

Elimination or neutralisation of the various natural oscillations in the apparatus is desirable to improve the quality of the sound or musical tone and may be effected through compensation by means of an electrical system of the same frequency and damping as is possessed by the oscillating system, the action of which is to be paralysed.

In Fig. 20 is shown a reproducer 132 to which is connected a circuit with corresponding oscillation constants. This circuit comprises the inductance 133, the non-inductive resistance 134 and the ciondenser 135 which are connected in series and are variable. The resistance and the inductance in particular, are preferably variable individually.

As represented in dotted lines in Fig. 20 the arrangement may also be such that the circuit of these oscillation constants, comprising the inductance 133, the condenser 135 and the non-inductive resistance 134 is connected in parallel with the reproducer 132.

Should natural oscillations of various parts exist, for example, if the horn of the loud-speaker possesses a natural oscillation and the diaphragm of the loud-speaker possesses another natural oscillation, a compensating oscillating circuit of the same period is employed for each natural oscillation, the circuits being connected either in series or in parallel.

Fig. 21 shows such a series connection.Three oscillating c circuits 137, 138, 139 each of which comprises an inductance. a non-inductive resistance and a condenser, are shown connected to the reproducer 136.

According to Fig. 22 the arrangement may be such that parallel to the reproducer 140 are connected the oscillating circuits 141, 142, 143, each consisting of an inductance, a capacitance and a non-inductive resistance.

These means for eliminating the natural oscillations may find general application beyond the example stated above, for instance in sound amplifiers of any kind or their equivalents.

The variation of the quantitative composition of the over-tones in the sound or musical tones may be effected by various deformations of the primary alternating current, by utilising the curved parts of the amplifier characteristics.

Fig. 23 illustrates such a system of connections. The oscillator or amplifier 144 supplies the transformer 145, the secondary winding of which controls the reproducer 146. A variable inductance 147 with a correspondingly variable capacitance 148 are connected in parallel with the reproducer. If the inductance alone is used, the over-tone frequencies pass through the reproducer. If the capacitance alone is used, the over-tone frequencies pass through the condensers and do not affect the reproducer. If both the inductance and capacitance are used together, the correct composition of the over-tones is obtained. Instead of the arrangement described, a variable choke coil149 and a variable condenser 150 may be connected in series with the reproducer 146 as indicated in dotted lines. In this case, the connection 151 is eliminated in this case also.

Fig. 24 illustrates a simple expedient for varying the characteristic of one of the amplifiers for example. The plate potential of the amplifier 152 for the reproducer 153 may be varied by the adjustable resistance 154. The cathode current may be varied by the rheostat 155, or the grid potential by the rheostat 156. The connection to the other parts of the system as shown in Fig. 2 is effected by the transformer 21.

In the selection of such characteristics as are required for the given proportion of over-tones, perfect results may be obtained by the combination of the characteristics of various electro-ionic tubes, for instance by the parallel connection of tubes with different operating characteristics.

In the diagram of Fig. 25 the transformer 21 which may be connected to the system of Fig. 2 controls the grids of four amplifiers 157, 158, 159 and 160. From each plate of said amplifiers, current flows to the reproducer 165 and the anode battery 166 through rheostats 161, 162 and 164, one for each amplifier. One of the rheostats 167, 168, 169 and 170 is arranged in the filament circuit of each amplifier. These resistance’s correspond to the resistance’s 154 or 155 of Fig. 24. However, the corresponding resistance 156 is eliminated in this system. The system of Fig. 25 affords more delicate graduations than that of Fig. 24.

The timbre is regulated in the above cases by varying the characteristics of the tubes by suitably adjusting the resistances.

Fig. 26, illustrates a system of connections for varying the timbre by varying the magnetic induction of the transformer core connected in the plate circuit of one of the amplifiers. The primary winding 171 of a transformer 172 is connected in the plate circuit of an amplifier. A secondary winding 173 is connected to the reproducer 174. The transformer is furthermore provided with a third winding 175, the energisation of which is varied by the rheostat 176. By adjusting the rheostat 176, the magnetisation of the core 172 is changed which causes a variation of the timbre in the reproducer 174. This system is simpler than that according to Fig. 25 but does not give gradual adjustment.

Fig. 27 is a diagram of a complete instrument for two tones. The system comprises two “sound-generating” control elements 177 and 184, for the first and second tones respectively, and a “sound-volume”control element 207.

Schematics

Technical