US1998620A

US1998620A - Dynamic control by intertube coupling devices

Info

Publication number: US1998620A
Application number: US656813A
Authority: US
Inventors: Jr John Hays Hammond
Original assignee: HAMMOND HOLDING CORP
Current assignee: HAMMOND HOLDING Corp
Priority date: 1933-02-15
Filing date: 1933-02-15
Publication date: 1935-04-23
Anticipated expiration: 1952-04-23

Description

April 23, 1935. J. H. HAMMOND, JR

DYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Filed Feb. 15, 1933 3 Sheets-Sheet 1 April 23, 1935. J. H. HAMMOND, JR 1,993,520

DYNAMIC CONTROL BY IIITERTUBE COUPLING DEVICES Filed Feb. 15, 1955 3 Sheets-Sheet 2 \J gnveniioi flame/1 1 5 yzw 47 4%. 2

April 23, 1935.

J. H. HAMMOND, JR

DYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Filed Feb. 15, 1933 3 Sheets-Sheet 3 Patented Apr. 23, 1935 UNITED STATES PATENT OFFICE DYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Application February 15, 1933, Serial No. 656,813

14 Claims.

The invention relates to amplifying systems used for reproducing music or speech from sound records and more particularly to means for controlling the gain ratio of .such amplifying systems.

According to the invention, the gain ratio of a multi-stage vacuum tube amplifier is controlled by varying the impedance of the coupling between stages. This does not change the operating points of the tubes. This impedance may include another vacuum tube which will be called, for purposes of description, a coupling tube. The impedance of this tube may be controlled by the potential of its grid which, in turn, may be controlled by the dynamics of the sound fed to the amplifier.

The control of the gain ratio may be such as to amplify the louder notes more in proportion than the softer notes. This is often desirable in reproducing sound from a sound record or talking film where normally the contrast between loud and soft notes is not sufiiciently emphasized for perfect reproduction. Or, the gain ratio control may be arranged to have just the opposite effect, that is, to amplify the softer notes more in proportion than the louder notes. If desired, a reversing switch may be provided so that the amplifier be changed from one type of operation to the other immediately.

The invention also consists in certain new and original features of construction and combination of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Fig. 1 illustrates diagrammatically a circuit 7 according to the invention;

Figs. 2 to 4, inclusive, illustrate modified circuits having different types of variable impedance intertube coupling devices; and

Fig. 5 illustrates diagrammatically the operation of the circuit shown in Fig. 1.

In the following description and in the claims, various details will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will permit.

Like reference characters denote like parts in the several figures of the drawings.

In the drawings accompanying and forming part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understood that'the details may be modified in various respects without departure from the broad aspect of the invention.

Referring now to the drawings, and more particularly to Fig. l, the system as shown comprises the amplifier tubes 22, 24, 21 and push pull amplifier 44 of a multi-stage vacuum tube amplifier. Tube 25 constitutes the coupling tube for varying the impedance of the coupling between tubes 24 and 21.

Sound energy is supplied to the amplifier tube 22 from a sound record which may be either on a moving film or on a rigid wax record.

In the drawings, light from a source [0 is focused by a lens H through an aperture l2 in the aperture plate 3 upon the sound track of a. moving film M. The light which passes through the film I4 is focused by means of a lens H4 upon a photoelectric cell l5 which changes the light variations into electrical variations. These variations pass through transformer I 6 to the double-pole double-throw I switch I I.

For receiving sound from a disk or other wax record (not shown) a pick-up I8 is providedwhich is also connected to a double-pole doublethrow switch ll. By operating switch I! sound from either type of record may be reproduced.

The switch I! is connected to a transformer 2| which is connected in the input circuit of amplifier tube22. The output circuit of tube 22 is connected to the input circuit of amplifier tube 24 through a transformer 23.

Connected to the output circuit of amplifier tube 24 is a choke coil 3|. In parallel therewith is the coupling tube 25. The choke coil 3| and coupling tube 25 are connected to the input of the next amplifier tube 2'! through a blocking condenser 26.

It will be noted that the plate circuit of coupling tube 25 and the choke coil 3| are in parallel and that variations in the impedance of the plate circuit of coupling tube 25 will vary the gain ratio of the amplifier.

change of coupling impedance in the plate circuit of the tube 24.

For controlling the impedance of coupling tube 25 a control tube 28 is provided whose input circuit is connected to the input circuit of amplifier tube 24. The output of control tube 28 is fed through transformer 29 to a rectifier circuit, including rectifier 35. Connected in circuit with the rectifier 35 through a 3-pole double throw reversing switch 36 is a biasing resistance 31 across which is connected a condenser 38.

C batteries 4| and 42 are connected to the reversing switch 36 and to the biasing resistance 31 so that the bias on the grid of the coupling tube 25 is determined by the battery bias, and the variable bias due to rectified current through resistor 31. C battery 34 gives the proper bias to the amplifier tube 21 through resistance 35. The A battery for supplying cathode heating current to the several tubes is denoted by 32 and the B battery for supplying plate current to the

tubes

21, 24, 25 and 28 is denoted by 33.

The output of the amplifier tube 21 is then fed through transformer 43 to a push pull amplifier 44 which in turn feeds a loud speaker 46 through a transformer 45. The stationary coil of the loud speaker is denoted by 41 and is energized by a source of direct current, indicated by 48.

In the operation of the circuit shown in Fig. 1, the switch I1 is thrown either up or down, according to whether it is desired to receive a selection from the moving film I4 or the pick-up I8. In either case the sound energy is amplified by the tube 22 and then impressed upon the next stage 24. The energy is further amplified by tube 24 and is impressed by means of the coupling devices 3| and 25 upon the next stage 21 where the energy is further amplified and fed to the push pull amplifier 44 which in turn feeds the loud speaker 46 in a manner which will be apparent to those skilled in the art.

The gain ratio of the multi-stage amplifier is controlled by varying the impedance of coupling.

tube 25. This is done by the energy which is amplified by the control tube 28 and which is rectified by the rectifier 35 and which passes through the biasing resistance 31 in a'direction depending upon the position of switch 36.

When the switch 36 is in its upper position the multi-stage amplifier acts as a volume expander. In other words, it so affects the dynamics of the sound impressed upon the amplifier that it amplifies the loud notes more in proportion than the soft tones.- When the switch 36 is in its lower position the multi-stage amplifier operates as a volume compressor and amplifies the loud notes less in proportion than the soft notes.

When the switch 36 is in the upper position the current from the rectifier passes through the biasing resistance in the direction of the upper arrow 5|. The C battery 4| is in series with the resistance 31 and assists the latter in impressing a negative bias upon the grid of coupling tube 25. The louder the sound the more current will flow through the biasing resistance 31 and the greater will become the negative bias on the coupling tube. This raises the impedance of the coupling tube 25 which increases the voltage impressed upon the next stage tube 21, which increases the amplification of the louder notes more than the soft notes.

When the switch 36 is thrown to its lower position the current through the biasing resistance 21 flows in the direction of the lower arrow 52 and both C batteries 4| and 42 are connected so as to oppose the resistance drop in resistance 31. Together, batteries 4| and 42 and resistance 31 control the bias upon the grid of the coupling tube 25.

In this case, the louder the sound, the greater will be the flow of current through the resistance 31. This will result in a decrease in the bias on the grid of coupling tube 25. This decreases the impedance of coupling tube 25 which increases the flow of plate current there through and decreases the potential impressed upon the next amplifier stage tube 21, resulting in a decrease in amplification with an increase in sound energy, and vice versa.

Fig. 5 illustrates diagrammatically the operation of the circuit shown in Fig. 1. In this figure the impressed signal is represented by the alternating current source I23 and the internal impedance of the electron discharge device 24 is represented by the resistance I24. The choke coil 3| is represented by the variable inductance I3I and the electron discharge device 25 by the variable resistance I25.

The system shown in Fig. 1, the operation of which is diagrammatically shown in Fig. 5. varies from other similar systems in that the impedance of the device 24, as represented by the resistance I24, remains substantially constant and the entire control is exercised by varying the coupling devices, represented by the variable inductance I3I and the variable resistance I25, between the stage 24 and the subsequent stage 21.

If desired, the choke coil 3| may be replaced by a non-inductive resistance, making the circuit resistance-coupled instead of inductance-coupled.

The operation of this modified form will be obvious from the description above.

Referring to Fig. 2, it will be seen that in place of an inductance coupling between amplifier tubes 24 and 21 a transformer 6| is provided. The coupling tube 25 is connected across the primary of the transformer 6| and operates to control the potential across the next stage tube 21 in a .manner similar to that described above.

Referring now to Fig. 3, the amplifier tubes 24 .and 21 are transformer coupled and a variable voltage transfer from secondary winding of transi former 6| to the grid of the tube'21.

Referring now to Fig. 4, amplifier tubes 24 and 21 are shown as coupled together by an inductance 66.. The iron core of this inductance is also wound with a winding 68 which receives rectified current from the rectifier 35, this current flowing in a direction depending upon the position of switch 65. Condenser 61 is provided to smooth out the current fiow through the winding 68.

When the switch 65 is in its upper position, the current flow through the winding 68 is in the same direction as the current through other winding of the choke coil 66 due to the .8 battery 33. Any increase in sound strength causes an increase in the current flowing through the coil 68. This will further saturate the iron core of choke coil 66, decreasing its permeability and decreasing the reaction of the choke coil 66 to the output of the amplifier tube 24. This will cause a greater sound current to flow through the choke coil 66 which will decrease the voltage impressed upon the next amplifier tube 21, which in turn will decrease the gain ratio of the multi-stage amplifier.

When the switch 65 is in its lower position, the

current through the winding 68 is reversed. In-

this case, increase in signal strength causes an increase in the permeability of the iron core of choke coil 66 which increases the reactance of this choke coil. This decreases the amount of sound current flowing through the choke coil,

. which increases the voltage across the next stage 21, which causes an increase in the gain ratio of the multi-stage amplifier.

It may be noted that the operation of Fig. 4 differs from that of Fig. 1 by emphasizing the change of reactance component of coupling impedance, whereas Fig. l emphasizes primarily changes of resistance component of the coupling impedance, with the reactance change an incidental efiect.

Thus it will be seen that a multi-stage amplifying system has been provided in which the gainratio is controlled by the impedance of the interstage coupling devices. The impedance is controlled by the dynamics of the sound impressed upon the amplifier either to compress the volume ratio or expand it.

While certain novel features of the invention have been disclosed and are pointed'out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without depart ing from the spirit of the invention.

What is claimed is:

1. In a system for use with a phonograph record, a multi-stage amplifier, a coupling device between stages of said amplifier, means for changing the volume ratio of the sound by varying the said coupling device, and a change over device for changing from volume expansion to volume compression.

2. In an amplifying system for use with a sound record, an amplifier comprising a first amplifier tube and a second amplifier tube, a variable impedance coupling said tubes, a control tube fed by the sound energy, a rectifier for rectifying the output of said control tube, means for varying said impedance comprising a control circuit fed by said rectifier to vary the gain ratio of the amplifier, and means for reversing the direction of the control current through said control circuit to either expand or compress the volume ratio.

3 In a phonographic system, a sound record, a translating device associated therewith, a multistage amplifier connected to said translating device, a second translating device connected to said amplifier, a transformer coupling between stages of said amplifier, a variable impedance tube having its plate connected across the primary of said transformer coupling and means controlled according to the dynamics of the sound for varying the impedance of said impedance tube.

4. In a phonographic system, a sound record, a translating device associated therewith, a multistage amplifier connected to said translating device, a second translating device connected to said amplifier, a transformer coupling between adjoining stages of said amplifier, a resistance across the secondary of said transformer coupling, said resistance comprising a fixed resistance and the plate circuit of a control vacuum tube in series therewith, and means controlled according to the dynamics of the sound for varying the impedance of said tube.

5. In a phonographic system, a sound record, a translating device associated therewith, a multistage amplifier connected to said device, a second translating device connected to said amplifier, an impedance coupling between adjoining stages of said amplifier, said impedance coupling having an iron core and a secondary winding and means controlled according to the dynamics of the sound for controlling the saturation current through said secondary winding.

6. In a phonograph system, a first translating device, a second translating device, a circuit between said devices, a coupling impedance in said circuit, and control means for varying the value of said impedance, said control means being governed by a moving average of the energy fed to said circuit by the first translating device.

'7. In a phonograph system, a first translating device, a second translating device, a circuit between said devices, a coupling impedance shunt across said circuit, and control means for varying the impedance value of said shunt, said control means being governed by a moving average of the energy fed to said circuit by the first translating device. v

8. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, a coupling transformer in said circuit, a resistance shunt across the primary of said transformer, and control means for varying the value of said resistance shunt, said control means being governed by a moving average of the energy fed to said circuit by the first translating device. i

9. In a phonograph system, a first translating device, a second translating device, a circuit between said devices, a transformer in said circuit, a resistance shunt across the secondary of said transformer, and control means for varying the resistance of said shunt, said control means being governed by a moving average of the energy fed to said circuit by the first translating device.

10. In a phonograph system, a first translating device, a second translating device, a circuit between said devices, an inductance shunt across said circuit, said shunt comprising a winding having a core of magnetic material and means for varying the saturation of said core, said means being governed by the moving average of the energy fed to said circuit by the firsttranslating device.

11. In a phonograph system, a first translating device, a second translating device, a circuit between said devices, an impedance in said circuit and control means for varying the value of said impedance, said control means being governed by a moving average of the energy fed to said circuit by the first translating device, the action of said control means being reversible.

12. The method of transferring sound to or from a sound record which comprises varying" sound record and expanding the dynamics of the sound which comprises translating the sound variations on the record into corresponding electrical variations, amplifying said electrical variations, passing said electrical variations through a variable coupling device, then further amplifying said electrical variations, translating the electrical variations as thus amplified into compressional sound waves, rectifying a portion of the electrical variations, and controlling the tightness of said coupling devices by said rectified electrical variations.

14. In a sound reproducing system, a sound record, a pick-up device therefor, a multi-stage least two vacuum tube stages having coupling devices between stages, a control channel fed by said pick-up device for controlling the gain of said amplifier, said control channel comprising a rectifier for producing a sub-audio control current, and means for causing said sub-audio control current to vary the tightness of a coupling device according to the moving average of the sound energy to expand the volume range of the audible signal.

JOHN HAYS HAMMOND, JR.