US2636989A - Electronic organ - Google Patents

Description

April 28, 1953 R. w. CHICK ELECTRONIC ORGAN 4 Sheets-Sheet 1 Original Filed Jan. 14, 1947 INVENTOR. f sssll. l1! (H/c4;

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R. w. CHICK ELECTRONIC dRGAN April 28, 1953 4 Sheets-Sheet 4 Original Filed Jan. 14, 1947 Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE ELECTRONIC ORGAN Russell W. Chick, Beverly, Mass., assignor to The Baldwin Company, Cincinnati, Ohio, a corporation of Ohio Original application January 14, 1947, Serial No. 722,049. Divided and this application January 23, 1952, Serial No. 267,804

duced have relied in general on gear-driven tone wheels or similar electro-mechanical tone generating devices. The most important object of my invention is to produce musical notes entirely by electronic means with the ultimate purpose of producing more satisfactory tones at less cost.

Another object of my invention is to provide means for locking a plurality of oscillators in fixed frequency relationship in which the several oscillators produce different frequencies but in a definite and stable relationship.

A further object of the invention is to prevent factors such as temperature changes and changes in the values of circuit components from causing frequency drifts in the oscillators of an electronic organ.

Another object of the invention is to provide an electronic organ in which a large number of notes may be placed in proper tuned relationship by means of a very small number of adjustments. For example, in an eighty-eight note instrument "it is one objective to tune the entire instrument by properly tuning twelve inductances.

One important feature of the invention resides in a master oscillator provided with automatic frequency stabilizing means.

Another feature of the invention resides in the combination of a stable master oscillator and a plurality of slave oscillators loosely coupled and arranged to oscillate at harmonics of the frequency of the master oscillator.

Another important feature of my invention relates to a novel transformer used for coupling the slave oscillators to each other and to the master oscillator.

Still another feature of the invention resides in a novel circuit with an associated automatic control system for producing a tremolo or vibrato effect by modulating the output of the final amplifier at a relatively low frequency.

These and other objects and features of the invention will be more readily understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings in which;

prises essentially a Wien bridge oscillator, gen- Fig. l is a circuit diagram for the master and slave oscillators,

Fig. 2 is a view in perspective of the coupling transformer,

Fig. 3 is a view in side elevation of the transformer,

Fig. 4 is a plan view of the transformer,

Fig. 5 is a view in end elevation of the transformer,

Fig. 6 is a circuit diagram of a second form of stable master oscillator, and

Fig. 7 is a circuit diagram of a tremolo circuit.

General organization The electronic organ of myinvention comprises a number of master oscillators arranged to produce audio-frequency oscillation of great stability, each master oscillator being coupled to a plurality of audio oscillators tuned to subharmonics of the master oscillator frequency and triggered or synchronized by the master so that all the oscillators are locked at predetermined frequencies. The oscillator are designed to produce notes very rich in harmonics. An amplifier and speaker are provided and connected to be driven from the oscillators through a special filter which can be adjusted to remove various percentages of the harmonics or add further harmonics in order to produce final notes of varying timbre in simulation of the instruments of the orchestra. A keyboard having a key for each oscillator is, in effect, a switchboard determining which oscillator, or combination of oscillators, is connected to the amplifier. A special circuit is coupled between two of the oscillators and the amplifier and arranged to modulate the amplifier by the difference of the frequency produced by beating together the output of the two oscillators. The result is a pleasing tremolo or vibrato effect.

With this general explanation in mind the following detailed description of some of the elements of the organ will be better understood.

The master oscillator The master oscillator i organized about the triodes VI and V2 as shown in Fig. 1 and comerally recognized as a special form of an R. C. oscillator. Inasmuch as the master oscillator is to fix the frequency of a many as eight toneproducing oscillators, as will later be described, it is imperative that the frequency of the master oscillator be stable. If the frequency drifts, it is not a question of detuning one note; it will affect an entire group. If one note of an instrument is out of tune, the effect is not too serious, but if several notes are out of tune, the result is apparent even to the most unmusical listener.

Those skilled in the art will readily appreciate that the resistor generally connected in series between the grid of VI and the coupling condenser C3 leading to "the plate V2 has been replaced by an inductance Ll, in Fig. 1, preferably a high Q, low resistance coil. It will be furthermore appreciated that the frequency of the oscillator may be varied by changing one or more of the circuit elements R2, Cl, or C3. The frequency or oscillation, assuming that the amplifier tube V2 has zero phase shift, is given by theequ-atinn:

(assuming that Ll has been replaced by the conventional resistor RI If all the resistors and all the capacitors are equal, the equation becomes;

1 Qn-RO Any one of the circuit elements referred to in the equations may change in value as a result of change in the ambient temperature. Furthermore some of the elements may change 'in value with age. It can be shown by experiment as well as -mathen'iatica'lly that a decrease in the value of R2, Cl or 03 will produce a corresponding increase in the frequency of oscillation. Conversely an increase in the value of R2, Cl or C3 will reduce the frequency of oscillation. Further-- more if an impedance be connected in the position of L2 in Fig. l, the frequency of oscillation will increase as the impedance of L2 is lowered. It has been established that the impedance of a coil increases with increases in frequency. Hence by inserting the inductance Li between the grid of VI and the coupling condense "leading to the plate of V2, I insert in the circuit an element tending automatically to compensate for frequency drift likely to be encountered in the operation of the oscillator. If the frequency tends to increase as the result of a lowered value of R2, Cl or C3, the immediate result will be an increase in the impedance of LI which in turn lowers the frequency of oscillation.

For additional frequency stabilization I have connected L2 in shunt with Li and R2, the grid bias resistor for Vi. One function of L2 is to vary the shunt impedance across R2 and L1 in the followin manner. If the frequency of the circuit should tend to rise, the impedance of L2 also rises and consequently reduces the frequency of the oscillator. By proper selection of the value of L2, the correct amount of compensation may be introduced. Another function of the coil L2 is to control the amount of regenerative feed-back reaching the control grid of the tube VI. As the impedance of th inductance L2 increases with an increase in frequency, the amount of feedback voltage increases; the increase in feed-back voltage in turn reduces the frequency of oscillation.

Furthermore, should the frequency of oscillation decrease, the impedance of L2 likewise decreases. thus decreasing the shunt impedance across R2 and Li and resulting in an increase of frequency of the oscillator. Accordingly it will be seen that I have provided means for stabilizing the frequency of the oscillator against factors which would otherwise result in varying'the frequency either up or down over a narrow range. Inasmuch as the frequency is affected by changes in the value of the condenser Cl I prefer to employ a silver-mica condenser orany suitable condenser exhibiting practically zero temperature coefilcient. Beneficial results will be obtained if all the circuit components are selected for minimum temperature coemcients.

It is to be understood that while I have inwanted a stable oscillator for supplying the triggering "or synchronizing impulses to the slave o cillators, my invention also relates to the combination of a source of triggering impulses of stable frequency and the slave oscillators coupled by a novel form of transformer for operation at fundamental frequency of the master and harmonics :or sub-harmonics thereof. Consequently the master oscillator may take many .forms, including mechanical or electro-mechanical sources of .osci-llations. The master oscillator shown Fig. :1 isisatisfactory. In Fig. 6 I have shown another form of master oscillator which I havefound preferable for reasons of economy and because it is inherently more stable. Furthermore the frequency us not affected by line voltage variations of as much as 150%.

In general organization the master oscillator shown in Fig. 6 is what is generally referred to as a two-terminal io'scillator. That is to say, a second triode is used as apha-se inverter in place of the more :convantional'tickler coil. As shown, the oscillator is formed about adual triode so, for "example a 6SN7. The plates :are supplied from 58-}- through a pair of plate load resistors 32, a filter condenser being connected across the line to smooth out ripples. The grid of the second triode is connected through a coupling condenser 135 to the plateof the first triode, and the plate of thesecond triode is connected through a coupling condenser 88/and :a resistor to the grid of the first izriode. The condenser '88 and resistor 9!! supply the necessary feed back voltage to the grid of the first triode to maintain oscillation. In the grid-cathode circuit 'of the first 'triode there is connected a tank circuit including a variable inductance coil $32 and a condenser Fl l. For temperature stabilization the condenser is preferably of the silver-mica 'type or other construction displaying a negligible temperature coefiicient. The cathodes are biased conventionally by means of a pair of resistors '96. A condenser 19%] is placed physically adjacent the condenser 88 and issu'bject to the same temperature effects. It is connected t ground and to the junction of the condenser 88 and the resistor 90. The ratio between charges on the condensers 88 and iilfi will remain very nearly constant in spite of temperature changes and their joint function is to maintain the feed-back voltage constant, thus tending to prevent frequency drift.

The capacity of the condenser 95 is purposely made high, i. e, 20,000-50,000 mmfd, in order to minimize input tube capacity effects which may be about 3.0 ,mmfd. Changes in tube capacities are thus minute in comparison with the tank circuit capacity and .have no effect on the frequency of the output. The coil 92 should be a high Q coil with minimum D. C. resistance.

The resistor not only provides the feed-back path but also tends to isolate the tuned circuit from variations in tube characteristics and voltage variations, the effects of long use of the tubes, etc. In determining the value of the resistor 98 a number of factors must be recognized, including the mu of the tubes, the plate resistance, and the resistance offered by the tank circuit. The critical value is given by in which Re is the critical value of the resistor 90; BL is the impedance of the tuned circuit at resonance in shunt with the grid-cathode impedance of Vi; u is the amplification factor of the tube, and Rp is the plate resistance. It follows therefore that by employing high resistance for R0, the feed-back voltage will change very little if at all in response to changes in RL, u, or Rb. Consequently I use a resistor of 500,000 to 1,000,000 ohms.

To recapitulate somewhat, the two-terminal oscillator shown in Fig. 7 is rendered satisfactorily stable by the combination of the condenser E00 connected as shown and disposed adjacent the condenser 88; the high resistance 90; and the silver-mica condenser 94.

The oscillator shown in Fig. 6 is provided with a line I02 leading from 13+ to the first winding on the transformer shown in Fig. 1, a line 504 leading from the cathode of the second half of the triode S0 to the grid of the tube V3 of Fig. l and including an isolating resistor Hi5 and a coupling condensor i536. The line I08 is a ground connection. A filter conden er HE is connected from the B+ supply line H02 to ground as line I08.

The slave system I The output of the stabilized oscillator is taken from the cathode of the amplifier tube V2 and fed to the grid of a triode V3 connected as a buffer and amplifier and including in its plate circuit a coil l0 wound about one end of a long core i2. The output is taken from the coil l0 through a blocking condenser I l and a series resistor [6 to a binding post l0 mounted in a strip 25!. As shown in Fig. l the core l2, in addition to the coil i0 has six other windings 22 each of which is included in the grid-plate circuit of a conventional locking oscillator. The blocking oscillators are organized about triodes V4, V5, V 6, V1, V8 and V0 and are all alike except that the circuit constants are varied. For example the frequency of the master oscillator may be fixed at 3520 C. P. S. and the blocking oscillators set at sub-multiples i. e. V i-4760; V5880; V64l0; Vl'-220; V8-1l0; and V055. The assembly shown in Fig. 1 will therefore produce seven notes each an octave apart and provide the As for an organ. I contemplate providing other assemblies to produce the other notes of the chromatic scales. The number of notes is not critical and is entirely a matter of choice; eighty-eight notes is the conventional number.

The master oscillator and all the slaves produce notes rich in harmonics; by means of ancillary circuits (not shown) I may remove various percentages of certain harmonics and thus provide means for simulating accurately the timbre of many instruments of the orchestra.

It is not necessary that each slave per se be precisely tuned to oscillate at the required frequency. By choosing the circuit components to make each slave oscillator oscillate near the required frequency, I achieve the desired result. The impulses from the master oscillator act as trigger impulses and lock the slave oscillators successively at the required frequencies. This is an important feature of the invention because it permits the slave oscillators to be assembled with relatively inexpensive components and with side tolerances. If the master oscillator is set to produce impulses rich in harmonics about a fundamental of 3520 C. P. 8., and the first slave oscillator Vii will naturally oscillate at about 1700 C. P. S., the effect of the master oscillations inductively coupled into the grid-plate circuit of the oscillator V 4 will be to change the frequency of the latter at once to 1760 C. P. S., and the master oscillator thus operates to synchronize or lock the slave oscillator at the required frequency.

The coupling between adjacent coils of the transformer is such that the amplitude, say, of the fundamental frequency in L3 is much greater than it is in L4. In L4 the amplitude of the subharmonic of the fundamental is much greater. So, in L5 the sub-harmonic of the frequency of the oscillator V5 is much greater in amplitude than that of the first sub-harmonic in V4. In other words the locking is a cascade efiect with each oscillator supply triggering impulses to the next one in line.

It is preferable to set the master oscillator at the highest frequency of the series of notes to be produced in the assembly. A change of one cycle per second in the trigger frequency of the master oscillator will be reflected in change of only /6; at the lower end, in the oscillator V9. On the other hand if the master oscillator was set at 55 C. P. E, a change of one cycle per second in the master oscillator would produce a change in 64 cycles in the high note of the assembly. A frequency shift of one cycle out of 3520 C. P. S. is not detectable by the human ear, but a change of 64 cycles is immediately evident, even at 5,000 O. P. S.

The transformer The success of the system depends in part upon the design of the transformer used to couple the master oscillator to the slaves and the slaves to each other. For one thing the amount of coupling is fairly critical. If the coupling is too close, all of the oscillators will operate at the same frequency. If the coupling is too loose, the desired locking effect is not obtained. I have found that a transformer constructed as shown in Figs. 2-5 may be used to great advantage. The transformer is organized about a special core formed of fiat rectangular plates made of silicon stee1 about .014 thick. I have found that a silicon steel well suited for the purpose is sold under the trademark Trancor. I provide a number of long plates 50 formed as two spaced stacks in which the plates are separated by short transverse interleaved stacks of silicon steel plates 52. Consequently the plates 50 are separated from each other by air gaps except at the areas shown where the alternate longer transverse stack plates 52 are interleaved.

In order to avoid too close coupling between successive blocking oscillators, I prefer to leave a wide gap in the centers of the long stacks on each side of the transformer. To obtain this effect I' leave out three long plates in the center of the long stacks. The effect is that the three inner plates are discontinuous, thus providing a larger air gap and consequent looseness in the coupling. Various combinations may be employed, and the specific arrangement shown in the drawings is to be considered as exemplary only. The assembly of the plates to and 52 is secured by any suitable fastening. About each one of the stacks of the plates 52 there is wound a coil contained between a pair of end plates as and provided with soldering lugs 62 attached to the ends of the coil and a soldering lug 54 attached to the center of the coil for a center tap connection. Each coil is covered by a protective layer 66 of treated fabric or paper. The winding of one of the coils is suggested in Fig. at the left end thereof where the covering 66 has been broken away to expose the windings 68. The sevaceeco eral coils are spaced apart equal distances by air gaps between successive covering layers 6b. This construction provides just the right amount of coupling. In a typical assembly, referring again to Fig. l, the coils L3 and L l may comprise 8,00% turns of No. 40E wire; the. coils L5, Lt, Ll and LB may comprise 10,000 turns of No. 40E; and the coil Lt may comprise 13,000 turns of No. 40E. Condensers C and C6 may be .01 mid; Ci

may be .02 infcl; C8 may be .03 mid; and C5 and CH) may be .1 mfd. The grid bias resistors l5 may then be given the values appropriate to set the slave oscillators at or near the required irequ'encies, in accordance with established practice.

One of the novel features of my invention resides in a circuit arranged to produce a tremolo or vibrato effect by varying the output volume rapidly. The preferred form of the tremolo circuit is shown in Fig. '7. A pair of triodes V3 and V i are: connected with parallel cathodes and plates and arranged otherwise as conventional amplifiers. The control grids are fed from the cathodes of two of the slave oscillators of the type shown in Fig. 7, the slave oscillators being so chosen that a beat frequency of roughly seven cycles per second is obtained on the plates of V3 and V4. For example, the slave oscillator producing A# at 116.5 C. P. 8. may be used in conjunction with the slave producing B at 123.5. The output from the triodes V3 and V4 wil1 therefore contain a beat frequency of '7 C. P. S. as well as 116.5 C. P. 8., 123.5 C. P. 6., and 240 P. 5. Con ventional grid bias and cathode bias resistors are shown as well as a cathode bypass condenser.

The primary winding of a transformer T3 is 1 connected in the plate circuit of the parallel triodes V3 and V4 with a condenser C 5 3 shunted across the primary. The secondary of the trans former T9 is shunted across a condenser Cd? and connected to the cathode, control, screen, or sup pressor grid (not shown) of one of the tubes in an amplifier 2M and to ground. The values of the condenser CM and Cd? are chosen to ofier very high impedance to frequencies of the order of 7-60 C. P. S. and very low impedance to higher frequencies. Consequently it is only the beat frequency of 7 C. P. S. which passes through the transformer rs and is applied to the amplifier 209.

A manually controlled switch 292 is provided to short-circuit the output of the transformer T9 when no tremolo effect is desired. In parallel with the switch 202 is a relay-controlled switch 29 the circuit for which will now be discussed.

If the tremolo circuit were continuous in its operation upon the opening of the switch 262, there would be an objectionable pulsing efiect audible to the listener when no keys were depressed and the instrument supposedly silent. Therefore I provide means for short circuiting the tremolo circuit output when no key is de pressed; however, it is not desirable to have the tremolo eifect shut on for the momentary pauses during the playing of a composition, as for example, during quarter or half rests. Accordingly, I provide time delay means for retaining the tremolo effect for a short time after a note has been played and all keys released.

The time delay relay circuit is organized about a double triode V5 and VB' and a relay 2% controlling the switch 204. One side of the relay 208 is connected to the primary winding of the transformer T9 which in turn is connected to 33+. One half V5 of the double triode is connected together and connected to one side of the output transformer T6 associated with the amplifier 200 and connected across a speaker 208. The cathode of the triode V5 is connected to the grid of the triode V5. The cathode of the triode Vii is biased from a voltage divider R913 and R connected from 13+ to ground, the bias being such that the triode V6 is cut off except when the triode V5 is conducting. The grid circuit of the triode V6 includes a resistor R52 shunted across a condenser CM, and the plate is connected to the relay 2%. A cathode by-pass condenser C lB is also provided.

Normally the switch 205 is closed to short circuit the output of the tremolo circuit and the relay is deenergized. When a key is depressed, the amplifier 29!! is driven and the transformer T5 carries current. The diode V5 then delivers positive bias for the grid of the triode V5 which consequently becomes conducting and energizes the relay 286 to open the switch 204 and permit the seven-cycle amplitude modulation of the amplifier Zllil from the transformer T9.

.When all keys are released, the transformer T6 delivers no A. C. voltage to the tube V5 and the tube VE is then out off by cathode bias sup ply. However, the swing to beyond cut-01f is delayed by the charge on the condenser C46 which gradually leaks off across the resistor R92 at a rate determined by the R. C. constant of C45 and R92. The time is therefore proportional to the values of C lt and RS2. When the condenser C55 has been discharged, the tube V6 is out olf and the relay 2% is de-energized; the switch 284 is closed. and the tremolo circuit is out off.

It should be understood that any convenient beat frequency may be obtained by choosing different slave oscillators to drive the tubes V3 and V4. Also I may provide a switch to select two out of three slave oscillators so that the player may select a fast or slow tremolo. For example, the circuit may be organized to provide a choice between a seven-cycle tremolo or a fourteen-cycle tremolo.

As with nearly all electronic devices it is possible to substitute equivalent circuits or portions of circuits in a device employing a combination of electronically performed functions. I believe the functions performed by the apparatus shown and described form a novel combination; I believe also that the particular master oscillator and tremolo circuits shown are novel per so as well as the physical structure of the transformer shown in the drawings. Some of the appended claims are expressions of my novel combinations of functions; others are specific to the details of the circuits or elements they described. I could not, without a fantastic multiplication of claims, drawings, and words, describe all the modifications and equivalents known to me. A competent electronic engineer will understand them and be able to produce an instrument embodying my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a generating system, a source of oscillations and a series of controlled generators, each of said controlled generators comprising a thermionic tube having a plate, a grid and acathode, a transformer having windings, a plate-to-cathode circuit containing one of said windings. in series and connecting said plate to asourceof pos-- itive potential, a grid-to-cathode. circuit containing the other of said windings in seriestherewith, meansfor transferring pulses from said source to the first of said generators to produce dis- 9 charges in the generator bearing a harmonic relation to said pulses, the transformers of the several controlled generators being inductively coupled one to another in a series whereby pulses occuring upon discharge in the first generator are transmitted to the circuit of the second generator and so on. i

2. In a series of serially controlled generators, each generator including a thermionic tube having a plate, a grid and a cathode, and each controlled generator having a transformer with windings located respectively in plate and grid circuits thereof, a structure comprising a common magnetic core, the windings of the transformers of a plurality of the controlled generators being located on said core.

3. In a series of serially controlled generators, each generator including a thermionic tube having a plate, a grid and a cathode, and each controlled generator having a transformer with windings located respectively in plate and grid circuits thereof, a structure comprising a com- 1 mon magnetic core with a plurality of core legs, the windings of the transformers of a plurality of the controlled generators being located individually on the said legs, said legs being con-,

nected together beyond the ends of said windings by core elements common to the several legs.

4. The structure claimed in claim 3 in which the said common core elements have less magnetic permeance than the said legs whereby to establish a condition of loose magnetic coupling between said. transformers.

5. The structure claimed in claim 3 wherein said legs are made up of laminations of magnetic material and wherein said common core elements are made up of a fewer number of laminations of magnetic material whereby to establish a condition of loose magnetic coupling between the said transformers, each leg bearing the windings of a transformer and lying in substantial parallelism to each other leg, and said common core elements lying in parallelism to each other and serving to interconnect the same ends of each of said transformer legs.

6. A transformer structure for use in a system for generating a plurality of h-armonically related frequencies, which system has a master generator and a plurality of controlled generators, said transformer comprising a plurality of substantially parallel legs, each of said legs made up of a plurality of laminations of magnetic material and each of said legs bearing the windings of a transformer in the circuit of a controlled generator, and a pair of substantially parallel core elements common to the said legs, one of said elements lying at each end of the assembly of legs and serving to interconnect the same ends of the said legs, said core elements being made up of laminations of magnetic material fewer in number than the laminations of said legs whereby to establish a condition of loose magnetic coupling between the several said transformers.

RUSSELL W. CHICK.

No references cited.

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