US2392384A - Automatic regulating system - Google Patents

Description

Jan. 8, 1946. R. v. HOWARD 2,392,334

AUTOMATIC REGULATING SYSTEM Filed July 19, 1944 2 Sheets-Sheet 1 A 00/0 OUTPUT INVENTOK 19w 2 360 A BY W i i d/V1010?! 477081147 R. v. HOWARD AUTOMATIC REGULATING SYSTEM Filed Ju'iy 19, 1944 2 Sheets-Sheet 2 mm? M .INVENTOR. 2 1 50wwu JDd/V/ 0100 V Patented Jan. 8, 1943 UNITED STATES PATENT OFFICE AUTOMATIC REGULATING SYSTEM Royal V. Howard," San Francisco, Calif. Application July 19, 1944, Serial No. 545,101

9 Claims. (01.179-171) My invention relates broadly to amplification systems and more particularly to an automatic gain control circuit for amplification systems.

One of the objects of my invention is to provide a circuit arrangement for an amplifier system in which changes in condition of the signaling energy at the input circuit of the amplifier system may be employed to automatically control the operating characteristics of the amplifier system for maintaining the level at the output circltit of the amplifier system substantially cons an I Another object of my invention is to provide a system of level control in which the amplifier circuit has the input thereof connected to the input circuit of a gain control amplifier and the, output circuit thereof connected to a limiter circuit with a differential circuit associated with the-composite output thereof for restoring the operating condition of the amplifier to counteract changing conditions in the .input circuit for maintaining the output leve1 in the output circuit substantially constant. p

A further object of my invention is to provide an electronically controlled compensation system for amplifier circuits whereby changes in the condition oflevel of the input have minimum efiect upon the level of output.

Other and further objects of my invention reside in the circuit arrangement for the automatic control system for audio frequency amplifier channels as set forth more fully in the specification hereinafter following by reference to the accompanying drawings in which:-

Figure 1 diagrammatically illustrates one circuit arrangement embodying my invention and Fig. 2 diagrammatically illustrates a modified circuit arrangement of my invention.

The advantages in the use-f the circuit of my invention will be apparent from the more detions he is receiving, nor can the operator control them if he is able to diflerentiate or correct wave form and energy content that the personnel tailed description hereinafter following. I may is unable to integrate or anticipate. Therefore, it becomes readily manifest that the ideal solution is some device of a purelyelectronic nature that win control and regulate the program to a finer degree than that'obtained by manual operation. Such a device permits a maximum utilization of the facilities and provides a more uniform output, eliminates human error to a great extent, and, further, eifects economy in manpower.

This desirable objective is not as easily obtained as might be apparently indicated, for one of the things that any device of this nature must not do is destroy the dynamic range of program content. Early experiment proved that it was not feasible or practical to put into use Just a slow operating volume control device,- for this had a constant rate of decay and, no matter how the constants were selected the desired results could not be obtained. It was noted, from observation over long periods of time, that what was needed was a device that, once regulated in its control, would not deviate in its gain regulation until a certain period of time had elapsed.

Then, if the program material 'was'low, the device would seek slowly, at first, to recover the deficiency. However, it is obvious that, once the lost gain has'been restored by the instrument,

it must be on the qui vive for any sudden applications of normal or excessive level. The device must also have the property of being able to reduce any abnormally high audio level to the applications.

motion picture systems wherein substantially constant level output is highly important. No matter how skilled or trained operating personnel may be, it is impossible to obtain maximum utilization of available facilities, be they recording, line transmission, or radio transmission, bymanual operation of volume. No matter-ho w judicious and adept the .personnel may be, individual errors, 1 occur due to the operatorss interpretation of the volume level indicating devices. Nor is it possible for the personnel to Judge whether the positive peaks or negative peaks are causing the indies-1 It was determined by extended research and measurements in standard broadcast practice that very rarely do program levels vary over a :10- db; Practical applications indicate that such a device in a radio transmitter shouldbe placed in a circuit before the, normal peak limiting amplifier, for this enables the constant use of the limiting amplifier at its maximum efliciency. It is ofcoursepossible and practical to incorporate the peak limiter into the' automatic device. y

'The amplifier system that is arranged between the inputvand outputcircuits of the audio frequency channel has the gain control or guardian bleeder (3.0 megohm) resistor Rn.

circuit at my invention connected substantially in parallel therewith so that the audio frequency variations which are supplied to the amplifier channel are also supplied to the input of the gain tion of values) due to the large size condensers,

restoration of signal would naturally result in an excessive output level for an appreciable period. The deleterious effect is overcome in' the autocontrol circuit. The gain control circuit has the 5 matic system of my invention by the use of a fastoutput thereof connected to the bias control circuit of the tubes oi the main amplifier system and also to a resistance capacity network havinga time constant which is determinative of the time control, or limiter device. This consists of the tube, in this particular-case marked SSR'I or 613.1, coupled to the output of the main amplifier or output stage. The diodes ofthis GSR'I or SR! gain rate of the main amplifier. I also provide'lo tube. system are biased at such a level that it a limiter circuit having its input connected with the output of the main amplifier system and connected to the resistance capacity network for the purpose of restoring the normal condition in the resistance'capacity network for counterbalancing input control can build up to the opposite eflects produced therein by program failure or gain reduction. That is to say,. the resistance capacity network operates as a differential circuit controlled in one condition acother condition according to the output program level. By the coaction oi. the gain control am; plifier with the main channel amplifier a d with the resistance capacity network and the limiter contributes no output during normal level operation; This limiter action therefore is to prevent excessive output levels. Its action applies voltage back through 8H6--23 until such a time as the its proper operating potential. 1

An adjustable arm marked 8 is provided on resistor Rm which is used to adjust the bias voltage which is connected at point 0 to the tubes cording to the input program level and in an- 6SN|2. If the level is too high or too-low, the

negative bias may be regulated by adjustment of tap 8 on resistor Ric.

'Meter Mi, shown in the circuit, is used as an indicating device that is calibrated to show the I am enabled to control with great precision the m t of regulation-of gain t t has t k program level supplied to the audio output circuit.

The system of my invention operates in such a manner" as to maintain essentially a constant audiooutput regardless of variations to the input level between certain desired limits. This control may be accomplished by utilizing the average level of rectified input signal asj the control voltage on an input stage containing variable MU tubes,

' as shown on the diagram. In the particular amsuiting D. C. potential is sumcient to control the 40 tenuation range of R1.

variable MU 8K|- l2 stage. The tubes marked 81-16- 2 and GHQ-'4 are utilized to obtain a difierential potential which charges condensers labeled C1 and Co at diflerent potentials: Con- 01 the voltage divider made up of the 0.5 and 1.0 megohmresistors Rio and R16 located betweenlHt-l and GHQ-2. Now as long as the potentialon Ca exceeds that on C1, the amplifier gain can not be increased as condenser C1, not having a bleeder circuit, holds the charge. If, however, the average input signal level to the, OHS-4 decreases, the charge on Co will leak oil! through its When'this potential is reduced to a value below that of C1,

diode BH6--.I conducts the charge accumulated main unchanged as it requires this interval oi,'

time for the charge on condenser Co to leak oi! to:a value equal to the charge on condenser Cm.

for a period exceeding 10 seconds, the gain in the ainplifier will be slowly restored toward a maximum. Since the control device is essentially a slow-time device (the time can be adiusted to any desired amount by the proper selecplace at any given time. I- provide a resistance network in series and shunt with meter M1 as shown at R0, R1 and Ra as required.

The upper section shown in the diagram comprises the main amplifier. It is represented as a mal input levelis intended to be about 20 db.

below standard reference level of 1' milli-watt in -.600 ohms, The minimum input level at which it will operate is approximately 25 db. The highest input levelpermissiblawill depend on the at- Normally the amplifier operates 10 dbsbelow its maximum possible gain 5b as to permit an automatic increase of 10 db. when the input level denser Ca receiv the higher potentialrbymeans 45 should drop" that amount. In the opposite direction the output remains essentially constant with an increase of 10 db. above the normal input level resulting in a control of i 10 db. or total range,

' at I leading through transformer T1 to the potentiometer system R1 grounded at 2 and then to the coupling system comprising condensers Cl and C: and resistors R2 and R: to the input circuits of v tubes OK'l-l and SKI-2.- The cathodecircuit s desired period of Ii, however, the input signal ceases or is reduced the gain control amplifier formed, by pairs of.

tubes which may be of the types represented at ISNl-l and lSN'|--2. The coupling between the.

tube stages is of the resistance capacity type constituted by resistors Rio. Rn. Ru and R1: interconnected by condensers C: and 04 as shown.

The tubes of'thefirst stage have their-cathodes connected to ground through resistor R while the tubes of the second stage have their cathodes connected to ground through resistor R14. The output of the second stage of amplification connects to the. transformer T3, the secondary of which connects to the double diodes represented 'at GHG-l, GHB-Z and 6H8--3. The output of the double diode SHE-l is coupled to the succeeding diode 6116-2 and 8H8-3 through the The power supply system includes transformer T0 connected to suitable source of power such as 110 volt 60 cycle alternating. .current through fuse potentiometer system RllivRl6 shunted by conof the double diode BHG-Z as shown. The anodes of this double diode connect to the anode and cathode of one section of the double diode 6H63 as shown, the cathode thereof having a resistor R'ze in series therewith as shown. The other section of the doubl diode 6H63 represented at D4 connects to the resistance-capacity network which includes condenser C1 and condenser Co shunted by resistor R11. a point in the circuit between diodes SHE-2 and 6H63 to the midpoint l2 between resistors R2 and R3 in'the coupling circuit of the main amplifier System. The program level control circuit 5 provides the variable bias for the control grids of the 6K1 tubes.' It is important that condenser C1 has no leakage as it must hold its charg until the voltage on condenser Ce leaks down to a value equal to that on condenser G1, at which time the gain increase rate of the amplifier is determined by the timeconstant of condenser Ca and resistor R11. .This'action occurs approximately 10 seconds after program failure. During the 10V second period no gain change takes place.

-.The center right section shown at 6 is the limiter circuit. Thi is necessary to hold the peaks down to normal level until the slow time control circuit has had suflicient time to seek itsnormal operating level. .This limiter acts only for two or three seconds at the beginning of'program. The limiter includes input transformer Ts which connects to the audio output system on the secondary side of transformer Ta. The output of transformer T5 has a potentiometer R thereacross connected through adjustable tap to the input of the limiter tube GSR'I or 6R1.

system T4 connects from tap it to the diode D4 leading to the resistance capacity network for restoring the charge to the condensersCa and A tap I0 is taken from F1 and S1. Transformer Tc includes'secondary windings 25, 2'6 and 21. Winding 28 supplies heating current for all of the heaters of the heater type tubes.

indicated at 80 or 5Y3. The anodes of the double rectifier tube are connected to opposite ends of secondary winding 26. .The output of the doublerectifier connects to the transformer circuit including condensers Ca, Ca and C10, and adjustable resistor R1: and inductances L1 and L2. The potential divider across the-output of the power supply system -contains resistors R19, R20 and R21 connected in its positive end to the anode supply cirv cuits in the gain control amplifier and limiter and at its negative and to ground indicated at 28. The

adjustable tap 29 on the potential divider R20 con-,

tubes SKI-f4 and SKI-2.

Adjustment procedure It is assumed that all tubes are operating properly. Set R1 about 16 db. below maximum gain. Set Ras for zero input. Potential dividerRn is selected of a value for obtaining maximum positive potential on the SHE-l cathode through adjustable tap 29 on potential divider R20. Now adjust Rs until M1 reads full scale. If this cannot be accomplished the value of .Ra should be altered. Now feed a 400 cycle audio signalinto the am-' plifler input at a level of about -20 db. below standard reference. Now reduce the positive bias on tube 6H6-.-l by means of adjustable tap 29 on potential divider R20 until M1 just begins to show a current reduction. Now increase the gain 10 db. by means of R1. M1 should now show ap proximately mid scale.- The adjustment of Ru can only be made approximate by means of a steady tone. A volume indicator should be connected across the output before the ladder attenuator as the level is rather low. Now increase the audio oscillator output of the volume indicator about 10 db. and observe the output level. Ric should be. adjusted until the output level shows a reduction of approximately -3 db. If it were not for the action of this negative bias on OSNI-J, the amplifier would be over controlled.

- The proper adjustment of this bias can only be made with actual program material feeding in as will be explained later. There remains the adjustment of B25. Feed an audio signal in just sufilcient to start current reduction on M1. Now remove GHS-l from socket. Increase the signal input 4-db. Now adjustRrs until M1 just begins C1. Th current through this circuit is reguwhen the entire system is operating normally.

to show current reduction again. This will be the proper adjustment.

Now for actual adjustment under program con- I dition's. An attenuator capable of 20 db. range should be inserted in the input to the amplifier.

and some program material connected to the input to the attenuator. Set the attenuator for 20 db. loss and adjust R1 until M1 just begins to show level 10 db. After several seconds-M1 should show: about mid scale and the output level should show the same level as previously noted. Now increase the input level another 10 db. and after several seconds note the output level. If the level is too Winding 21 supplies heating current forthe cathode of the double rectifier tube C 4 mi. paper, 600 volt 4 V high provide less negative bias for GSNl-2 by means of R18. If the level is too low, increase this bias. It may be necessary to make further adjustments of R21 and repeat the above procedure in order to secure a linear dynamic control characteristic which shows constant output with a total input variation of 20 db. The 6H6 tubes are preferablyglass in order to'reduce leakage.

I have listedhereinafter the values for the several circuit components which I have found most.

efiicient for carrying out my invention in the circuit of Fig. 1:

Ra Approximately 200 ohm, depends 011 meter used R a 1500 ohm, 1 watt R10 10,000 Ohm, 1 watt R11 10,000 ohm, '1 watt 500,000 ohm, /2 watt 500,000 ohm, /2 watt 1000 ohm, 1 watt 500,000 ohm, watt 125,000 ohm (regular volume control) 3 mega, /3 watt 2000'ohm wire wound 20 watts, slide wire 5000 ohm wire wound 20 watts 5000 ohm wire wound, slide wire, 10 watts 100 ohm wire wound 250,000 ohm, /2 watt 1500 ohm, 1 watt 75,000 ohm, 1 Watt 1 meg. (regular volume control) /2 meg, /2 watt .01 mi. mica condenser .01 mi. mica condenser I .05 mi. paper condenser, 600volt .05 mi. paper condenser, 600 volt '2 mf. paper condenser, 400 volt 2 mi. paper condenser, 400 volt C7 A; mi. Pyranol, 600 volt Cs 4 mi. paper, 600 volt or equivalent electrolytic condenser C9 4 mf. paper, 600 volt or equivalent electrolytic condenser R13 R14 R15 R16 R17 R18 R12 R20 R21 R22 R23 R24 R25 R28 C1 or equivalent electrolytic condenser C11 .1- mf., 400 volt paper condenser C12 25 mv., 150 volt electrolytic condenser T1 Well shielded input transformer, line to grid,

good quality T2 Output transformer, approximately 10,000

ohm primary to 500 ohm secondary T3 Approximately 20,000 ohm primary, one to one ratio overall T4 Approximately 10,000 ohm primary, ratio primary to one-half secondary one to one Referring to Fig. 2 of the drawings it will be seen that the voltage from transformer T-3 is fed to the tube labeled GHG-l. The rectified output of tube liH6---l is impressed across con- R15 and R16.

denser C5 which has shunted across it resistors sistor identified as R26 to the control line l0, connecting to point l2 intermediate resistors R2 and R2. The other cathode of SHE-2 is connected at point 8 of R16 which is adjustable. The other plate of tube SHE-2 shown at D-4 is connected to thecontrol circuit l0 which is connected to ground via a one-half microfarad condenser identifled as C7.' The limiter circuit derives its voltage from 6K|-l and 6K1-2 which is applied through suitable blocking condensers to the grids of tube 5SN1--3 whose plates are coupled to an output transformer labeled T4 whose secondary is coupled to' tube SHE-4. The output of this circuit is connected to a stabilizing resistor. R2; to diode D6 of tube 6H63 in the arrangement shown in Fig. 2', whose late is connected to control circuit l0. v i I A connection is made at the cathode of tube "SHE-4 of diode D--l whichconnects with the cathode of diode D5 of tube 6H6'3. The plate of diode D-5 is connected through resistors R31- and Rza tothe cathode of tube 6SNl-3. Voltage is received from the output of tube .6H8--l which charges condenser Cs which has connected across-it resistors R15 and R111. Voltage is picked up from the adjustable divider at connection 8 on R16 which is impressed upon the cathode of D& of tube 6H6-2 which is then passed on via the plate of diode section D-d upon C5 is reduced by the action of the shunting resistors R15 and R16 to a point where its voltage is less than that of C1 of control circuit 80, then diode D--3 of tube 0116-2 conducts and the voltage across Cris reduced by the resistance of D-S and the other circuits and the decay charbias is obtained by the voltage drop occurring acteristics of this voltage are determined by re sistors Ra R16 and the resistance or diode M of tube 0H6-2. By such action the voltage on control circuit l0 connected to the control tubes is further reduced. and the gain of the controlled amplifier is increased. 'With no signal impressed on the output of the diodes of tube 6118-4 the of tube GHQ-3 and resistors R31, R21 and R112 T5 Input transformer, line to grid, 500 ohm to whose voltage is adjusted on. Ruby variable connection R32 therefore increasing the rate of control'through control circuit l0.

The center right section shown at 0 is a limiter circuit. This is necessary to hold the peaks downto'normal level until the slow-time control circuit has had suflicient time to seek its normal operating level. This limiter acts for approxi The voltage from 6H6-i plates tion.

reslstorRai. However until it is made inoperadiodes, a limiter circuit having lament-e9 tive, voltage is developed in the output circuit of tube lSN'l-3 which is fed to the cathodes of tube OHS-4 through transformer T4 through the load of the terminating resistor R2: to diode D-.8

of tube 6H6-3. The output of diode D-G is 1 connected to control circuit I0. This voltage is D 6 also reduces the voltage on the grids of 1 tube 6K'|- l2. 1 The fixed bias on diodes SHE-4 is supplied by tap 29 of potentiometer R20.

This bias regulates the point at which the operation of diodes of tubes 8H6l will come into operation.

I The peak limiter is definitely made inactive until slow-time control becomes inactive. The circuit of Fig. 2 has ,a finer limit of control. On this instrument the outputvoltage'becomcs linear after the control section has reached saturanected with the output of said audiofrequency amplifier channel, a connection between'the out put ofsaid limiter circuit and said condensers, and means interconnecting one of said con densers and said bias control circuit for correctlng the bias condition .of said audio frequency amplifier system to compensate for variations in level of the program incident upon the input circuit of said'audio frequency amplifiersystem.

2. In a system for controlling amplification level inaudio frequency amplifiers in combination an audio frequency amplifier channel inchannel, a condenser circuit having a substan- The components of the circuit of iig. 2 are substantially the same as'set forth in Figure l with the addition of the components illustrated in Fig. 2 which have values as follows:

meg., /2 watt /2 meg., /2 watt 1000 ohms, 1 watt 5000 ohms, 1 watt 1 meg., 1 watt C14 .05 mi. mica condenser C15 .05 mf. mica condenser tial time delay discharge rate connected with the output circuit of said gain control-amplifier, a

charge accelerating circuit connected between said main amplifier andsald gain control ampliand R3 to meg. It will be understood, however, that I have made reference herein to val ues merely for the purpose of explaining certain preferred embodiments of my invention and that I have no desire to restrict the components to the particular values shown. As heretofore noted the control system of Fig. 2 is in certain.

installations more effective than the control sysmm of Fig. 1 as the circuit of Fig. .2 exerts a and types of the circuit components and I intend no limitations upon my invention other than may be imposed by the scope of the appended claims. What I claim as new and desire to secure by Letters Patent of the United States is as follows: 1. In a system for controlling amplification level in audio frequency amplifiers in combination an audio frequencyamplifier channel ineluding an input circuit, an output circuit and a bias control circuit, a gain control amplifier having its input circuit connected with the input circuit of the aforesaidaudio frequency ampli-' fier channel, pairs of diodes connected with the output circuit of said gain control amplifier, 'a

condenser connected with the output of one of said diodes, 'a condenser shunted by a resistor connected with the output of the other of said mentioned network and the bias control circuit fier, a multiplicity of-isolating diodes connected with the output of said gain control amplifier, a

resistance shunted by a condenser connected with one of said diodes, a condenser connected with the other of said diodes, a limiter circuit connected with the output of said main amplifier, and circuit connections between said diodes, said condensers, said limiter circuit and between said condensers and said bias control circuit for flu-- pressing bias potential upon the bias control circuit of said main amplifier proportional to changes in the operating conditions in the output circuit of said main amplifier.

4. A control system for amplifiers comprising in combination with a main amplifier including a bias control circuit therefore,-a gain control amplifierhaving a bias control circuit, means for simultaneously feeding both said main amplifier and said gain control amplifier, a multiplicity of isolating diodes connected with the output of said gain control amplifier, resistance capacity networks connected with each of said diodes, a connection between one of said networks and the bias control circuit of said gain control amplifier, a connection between another of said networks and the bias control circuit of saidmain amplifier, and a limiter circuit interconnecting said last of said main amplifier. 5. 'A control system comprising an amplifier having an input circuit. a bias control circuit and an output circuit, a gain control amplifier having input, bias control and output circuits, a parallel feed circuit for each of said input circuits, a dif- .ferential control circuit connected with the output circuit ofsaid gain control amplifier, a limiter circuit connected between the output of said main amplifier and said difierential circuit, and con- .nections between said differential circuit and the bias control circuits of said main amplifier and said gain control amplifier for determining the bias potential on said main amplifier by the con- 8, A control system comprising an amplifier .joint action of said gain'control amplifier-and saidlimiter circuit upon said difierential circuit. 6. A control system comprising an amplifier having an input circuit, a bias control circuit and an output circuit, a gain control amplifier having input, bias control and output circuits, 9. parallel feed circuit for each of said input circuits, a capacitative circuit connected with the output circuitof said gain control amplifier and operative to' be discharged thereby according to decay in the current supplied to said input circuits, a connection from said capacitative circuit to the bias con& trol circuit of said gain control amplifier, a connection from said capacitative circuit to the bias control circuit of said first mentioned amplifier,

and means interconnecting said capacitative circuit with the output circuit of said first men-' tioned amplifier for restoring the, charged condition of said capacitative circuit and maintaining predetermined biased condition of the bias circuit of said first mentioned amplifier.

. connection from said capacitative circuit to the bias control circuit of said first mentioned amplifier, a limiter circuit comprising a resistance having an input circuit, a bias control circuit and an output circuit, a gaincontrol amplifier having input, bias control and output circuits, a parallel teed circuit for each oi'said input circuits, a capacitative circuit connected with the output circuit'oi said gain 'control amplifier and operative to be discharged thereby according to decay'in the current supplied to said input circuits. a connection from said capacitative circuit to the bias control circuit of said gain control amplifier, a connection from said capacitative circuit to the bias control circuit of said first mentioned amplifier, a resistance network, means for in combination with a main amplifier including a" networkconnected with'the output of said first mentioned amplifier, and an accelerating amplifier connected with said resistance network with the output thereof connectedto said bias control circuit for accelerating the restoration of said bias control circuit to a predetermined normal operating condition.

capacitatively connecting said resistance network to the output circuit of said first mentioned amplifier, and an accelerating amplifier connected with said resistance network and connected with said bias control circuit for restoring said bias control circuit to a predetermined bias control condition. y

9. A control system for amplifiers comprising bias control circuit therefore, a gain control amplifier having a bias control circuit, means for simultaneously feeding both said main amplifier and said gain control amplifier, a multiplicity of isolating diodes connected with the output of said gain control amplifier, resistance capacity networks connected with each of said diodes, a connection between one of said networks and the bias control circuit of said gain control amplifier, a connection between another of said networks and the bias control circuit of said main amplifier, a resistance network, means for capacitatively connecting said resistance network with the output of said first mentioned amplifier, an

- electron tube acceleratingcircuit connected with said resistance network and connections from said electron tube accelerating circuit to said bias control circuit .for expediting the restoration of ROYAL V. HOWARD

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