US3496452A

US3496452A - Automatic volume control

Info

Publication number: US3496452A
Application number: US592896A
Authority: US
Inventors: Gilbert J Vollink
Original assignee: Rowe International Inc
Current assignee: Rowe International Inc
Priority date: 1966-11-08
Filing date: 1966-11-08
Publication date: 1970-02-17
Anticipated expiration: 1987-02-17

Description

Fb. 17,1970 G. J. VbLLmK 3,496,452

u AUTO MATIC VOLUME CONTROL Filed Nov. 8, 1966 2 Sheets-Sheet 1 Ian a? 1 N INVENTOR.

2 Gi/beri J Vo///m( BY ,(Mmwfa m/ RTTORN E Y5 Feb. 17', 1910 v G, J. VOLLINK 3,496,452

AUTOMATIC VOLUME CONTROL Filed Nov. 8. 1966 INVENTOR.

Gi/berf J. Vo/b'n" ATTORNE Y5 United States Patent 3,496,452 AUTOMATIC VOLUME CONTROL Gilbert J. Vollink, Grand Rapids, Mich., assignor, by mesne assignments, to Rowe International, Inc., Whippany, N.J., a corporation of Delaware Filed Nov. 8, 1966, Ser. No. 592,896 Int. Cl. Gf 1/40 US. Cl. 32321 15 Claims ABSTRACT OF THE DISCLOSURE A fast attack time, relatively slower release time automatic volume control circuit comprises a main capacitor which normally provides a regulating voltage for a lamp, the brightness of which controls the amplitude of an output signal, which may be of audio frequency, as from a record player. Whenever the output signal amplitude exceeds a certain level, an auxiliary capacitor immediately discharges. It then recharges from the main capacitor to produce a rapid and predetermined reduction in the output signal amplitude.

Background of the invention There are known in the prior art coin operated automatic record playing devices or jukeboxes. These devices are required to play a great variety of various brands, sizes and speeds of records.

In playing a record the background level and the sound level are a function of the depth of the needle grooves and the amount of lateral movement permitted for the needle. The lateral movement in turn is a function of spacing between adjacent grooves on the record. This groove spacing not only varies from manufacturer to manufacturer but, also, it varies with one manufacturer depending upon the amount of recorded material he desires to fit onto a single record.

It will readily be apparent from the foregoing description that for material of relatively short duration on a single disk, wide spacings are employed and a relatively high sound level is readily attained. On the other hand, where material of long duration is compressed onto a single record disk, the spacing between the grooves must of necessity be small and the resultant sound level is consequently low. This latter problem is of special importance in the use of small, long-play record disks now widely used in jukeboxes.

Coin-operated automatic record players of the type described above must be able to play records of all the types described above which may be mixed in the same machine and it must play them with approximately the same audio output level.

In an attempt to solve the problem of playing various records having diiferent groove spacings in machines of the prior art, there is provided an automatic volume control arrangement in which the amount of signal shunted from the output is determined by the illumination of a lamp which lights a photo-responsive device. In a system of this type, a signal level responsive circuit provides a voltage for the lamp which increases with increasing sound level to shunt more of the sound to limit the output sound level. It may be a capacitive circuit which discharges in response to signal level above a predetermined level.

For proper operation of a circuit of the type described, the attack time, or time required to produce a lamp voltage change in response to a signal level change, cannot be too long or pulses of sound, or envelope pulses, will not permit a sufficient change in capacitor voltage to give a significant decrease in lamp voltage. On the other hand, the attack time cannot be too short since the lamp has an inherent lag in responding to change in the voltage applied thereto. In other words, the lamp illumination will not change immediately with a change in the voltage applied thereto. As a result, the attack time, while not being too long, should be appreciably longer than the lag in lamp response.

I have invented an improved automatic volume con trol circuit which solves the problems outlined above. My' circuit has a relatively short attack time While maintaining a relatively long release time, or time required for the circuit to return to equilibrium after a lamp voltage change. My automatic volume control circuit is especially adapted for use in jukeboxes. It minimizes the undesirable effect of sharp pulses of short duration in the sound level of the output. It provides an arrangement wherein the attack and release time of the circuit can independently be controlled. It provides a very constant output.

Description of the invention One object of my invention is to provide an automatic voltage control circuit having a fast attack time and having a relatively slow release time.

Another object of my invention is to provide an automatic voltage control circuit which is especially adapted for use in jukeboxes.

A further object of my invention is to provide an automatic voltage control circuit which responds to relatively sharp pulses of sound level of short duration.

A still further object of my invention is to provide an automatic volume control circuit having a very constant output.

Other and further objects of my invention will appear from the following description.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a schematic view of one form of my automatic volume control circuit.

FIGURE 2 is a schematic view of an alternate form of the output signal level responsive portion of my automatic volume control circuit.

FIGURE 3 is a schematic view of a further form of the output signal level responsive portion of my automatic volume control circuit.

FIGURE 4 is a schematic view of a still further form of the output signal level responsive portion of my automatic volume control circuit.

Referring now to FIGURE 1 of the drawings, one form of my automatic volume control circuit includes a suitable source of potential having a terminal 10 providing a voltage of, for example, 30 volts. The sound system of the device such, for example, as a jukebox with which my automatic volume control circuit is employed, includes a terminal 12 to which the signal from the pickup or the like is applied. A capacitor 14 couples this signal to the base of an amplifier transistor 16 having a collector resistor 18 connected to terminal 10 and having an emitter resistor 20 connected to ground.

Voltage dividing resistors

22 and 24 provide a bias for the base of the transistor 16. A resistor 26 couples the output signal of the amplifier 16 to the base of a transistor 28 and to one terminal of a shunting filter including a capacitor 30 and a photo-responsive resistor 32, the other terminal of which is connected to ground. As will more fully be explained hereinafter, the resistor 32 is disposed in a light-tight housing 34 together with a lamp 36 adapted to illuminate the resistor.

Transistor 28 has an emitter resistor 38 which provides the audio output signal at an output terminal 40. A filter capacitor 42 connected in series with a resistor 44 having a brush 46 and a resistor 48 between terminal 40 and ground provides a voltage at the brush 46 which is a measure of the sound level at the output terminal 40.

I apply the signal on brush 46 to the base of a silicon transistor 50 having a silicon diode 52 connected between its emitter and ground. A resistor 54 connected between terminal 10 and diode 52 provides a biasing voltage .for the diode. Transistor 50 has an inherent base to emitter delay of about one half volt while diode 52 also provides a one half volt delay with the result that there is an overall delay of one volt at brush 46 before transistor 50 is rendered conductive. I connect a resistor 56 and the main control capacitor 58 in series between terminal'l and ground. A resistor 60 connects the common terminal of resistor 56 and capacitor 58 to the collector of transistor 50. I connect the first auxiliary capacitor 62 and a resistor 64 between the collector of transistor 50 and ground. A diode 66 shunts resistor 64 to control charging of capacitor 62 in a manner to be described. The second auxiliary capacitor '68 shunts transistor 50 and diode 52. The signal on capacitor 58 is coupled to the base of an amplifier-transistor 72, the emitter of which is coupled to the base of a second amplifier-transistor 74, the emitter of which is grounded through resistor 77.

Transistors

72 and 74 have a common collector resistor 76. A conductor 78 applies the collector output voltage of transistor 74 to the lamp 36 through a l-volt Zener diode 79.

In one form of my automatic volume control circuit, resistor 56 will have a resistance of megohms. The collector resistance of transistor 50 with the device nonconductive may be approximately 10 megohms. Resistors 60 and 64 have respective resistances of K and 90K, while

resistors

76 and 77 have respective values of 670 ohms and 330 ohms.

Capacitors

58, 62 and 68 have respective values of 50 i, 9 pf and 1 pf. The current gains of

transistors

72 and 74 are 170 each.

The input impedance of emitter follower transistor 72 will therefore be (330) l70) =l0 megohms, as indicated in FIGURE 1.

Considering the circuit with the particular circuit parameters just described and with transistor 50 not conducting,

capacitors

58, 62 and 68 charge to a potential of 10 volts. The time-constant for this charge, which timeconstant is the release time of the circuit, Will be the equivalent resistance, which is approximately 3.3)(10 ohms, times the total capacitance, which is 60 10 farad, giving a time constant of 3.3 minutes. It will readily be apparent that the release time thus is relatively long. With the capacitor '58 thus charged,

transistors

72 and 74 will each have an emitter potential of substantially 10 volts; and transistor 74 will draw 30 ma. collector current. Accordingly transistor 74 will approach saturation with a collector potential of substantially 10 volts. However no signal is applied to lamp 36 because of the 10 volt drop in potential provided by Zener diode 79. Under these conditions the resistance of the device 32 is high and very little signal is shunted from the output at terminal 40.

Assume now that there is a relatively steady level of sound input which produces more than 1 volt at brush 46 and thus renders transistor 50 conductive.

Capacitors

62 and 68 now discharge very rapidly. Capacitor 58 continues to discharge through resistor 60 and transistor 50 with a time constant of 20 10 50 l0 or one second, which is the attack time of the circuit. This attack time, while being short, is relatively long compared with the lag in the response of lamp 36 which may, for example, be about 0.25 second. Capacitor 68 provides a low impedance to moderately low audio frequencies so that the collector of transistor 50 is maintained substantially at ground potential even though transistor 50 is gated on only during the positive peaks of the audio signal.

As capacitor 58 discharges in the manner described above, conduction through

transistors

72 and 74 is reduced, increasing the voltage applied to the lamp, and

increasing the illumination of resistor 32 to reduce its resistance and shunt more of the signal input of transistor 28 to ground. The signal at brush 46 is thus attenuated until it is only slightly in excess of one volt peak value.

'A steady state condition is reached with transistor 50 driven slightly into conduction at the positive peaks. Transistor 50 now acts more as a gated amplifier than as a true switch, since it will not be driven to saturation.

As a voltage amplifier, transistor 50 has an extremely high gain because of the large collector resistance. However voltage 50 provides a very low power output which is not sufficient to operate the lamp. The necessary power gain is provided by cascaded

emitter followers

72 and 74. This power gain is achieved with negligible drift since the voltage gains of the emitter followers are substantially unity irrespective of wide variations in their current amplification factors by virtue of the large degenerative or negative feedback. Transistor 74 of course provides a voltage gain of two at its collector output; but this small voltage gain is insignificant compared with the large voltage gain of the delayed, gated-amplifier 50. The performance of any delayed automatic volume control increases with the extent of amplification after the delay level is exceeded, provided such amplification is relatively free of drift. If such amplification is subject to drift, then the AVC system will be either rendered completely inoperative or subject to erratic operation depending upon whether the amplifier hangs up or saturates at one limit or the other. My AVC system provides high gain with low drift. The output signal at terminal 40 varies less than 1 db for inputs at terminal 12 ranging from 0.6 millivolt to mv.

Considering now the occurrence of a single short pulse in the input sound level as represented by its envelope, transistor 50 is rendered conductive for the duration of the pulse. When that occurs,

capacitors

62 and 68 immediately discharge. Then capacitor 68 rapidly recharges from capacitor 58 through resistor 60 with a time-constant of 20 milliseconds. This removes 2% of the charge from capacitor 58 which produces a sharp small drop in conduction of

transistors

72 and 74, and correspondingly, a sharp small increase in the voltage applied to lamp 36. Then capacitor 62 recharges from capacitor 58 at a rate determined by the total resistance 20K+90K and the capacitance 9 M3. in the charging circuit, or with a time constant of approximately one second, which is the same as the attack time of the system. With this sequence of events, the portion taken from the total charge of capacitor 58 is the ratio of the sum of the capacitances of

capacitors

62 and 68 to the total capacitance in the circuit, or about 0ne-sixth of the total charge. The signal at terminal 40 is correspondingly reduced by approximately 16.7% which represents a power attenuation of 0.8 db.

Assuming now a number of short imput pulses occurring within a period less than one second, transistor 50 is rendered conductive during each of these pulses. Upon each pulse, capacitor 68 instantaneously discharges and then rapidly recharges from capacitor 58, thus reducing the charge thereon by about 2%. After the last pulse, capacitor 62 recharges from capacitor 58 through resistors 60 and 64. The total voltage attenuation is 2% (n1)+16.7%; and the total power attenuation is 0.1 db (n1)+0.8 db, where n is the number of pulses.

Referring now to FIGURE 2, I have shown an alternate form of the signal responsive portion of my automatic volume control circuit. In the arrangement shown in FIGURE 2, I replace the resistor 60 with a resistor '80 rather than the 20K resistor 60 as in FIGURE 1. having a value of K between capacitor 58 and the diode 66. With these changes, the discharge path for capacitor 58 includes the parallel-connected

resistors

80 and 82 which, as will readily be appreciated, provide the same one second attack time as does the form of my cir-\ cuit shown in FIGURE 1. The recharging circuit for audio-filtering capacitor 68 comprises the 25K resistor 80 rather than the 20K resistor 60 as in FIGURE 1. The single 110K resistor 82 of FIGURE 2 replaces the series-connected resistors 60 and 64 of FIGURE 1 in the recharging path for capacitor 62. In all other respects, the circuit is the same as that shown in FIGURE 1.

Referring to FIGURE 3, I have shown one arrangement in which I connect

capacitors

84 and 86 in series rather than in parallel as is the case with

capacitors

62 and 68 in FIGURES 1 and 2. Diode 66 is connected directly between the common terminal of

capacitors

84 and 86 and the collector of transistor 50. A resistor 88 shunts capacitor 86. In this form of my circuit I select

capacitors

84 and 86 to have respective values of 10 f. and 1 ,uf. and I select resistor 88 to have a value of 80K. The discharge path for capacitor 58 is through the 20K resistor 60 as in FIGURE 1. Moreover, the 1 ,uf. audio filtering capacitor 86 recharges through the same resistor. However, the capacitor 84 charges through the series connected

resistors

60 and 88 from capacitor 58. The time constant in this case will be the same as in the form of the invention shown in FIG- URE 1.

FIGURE 4 illustrates a modified form of the seriesconnected capacitor circuit shown in FIGURE 3. In this form of the device, a 25K resistor 80 connects capacitor 58 to the collector of transistor 50. A resistor 92 having a value of 100K connects capacitor 58 to the anode of diode 66. The discharge circuit of capacitor 58 includes the parallel connected resistors. 80 and 92 providing a discharge time-constant of one second. Capacitor 86 recharges from capacitor 58 through the 25K resistor 80 while capacitor 84 recharges from capacitor 58 through the 100K resistor 92.

In each of FIGURES 2, 3, and 4, the delay bias is only one half volt as provided by silicon transistor 50, since silicon diode 52 has not been employed. Also transistor 72 is now assumed to have a current gain of 300. Only one emitter follower power amplifier is used; and its emitter resistor 77 has a value of 33K. The emitter follower input impedance is 33 10 300=l megohms as indicated in each figure. The collector resistor 76 has a value of 67K, which is assumed to be sufficiently low to operate a sensitive lamp. In the absence of an input signal, transistor 72 will be just at saturation and draw a conduction current of 0.3 milliampere. The collector output of transistor 72 will exhibit a voltage gain of two as determined by the ratio of collector and

emitter resistors

76 and 77. Again excellent AVC performance is achieved because of the extremely high voltage gain of delay amplifier 50 and the low-drift power gain of degenerative amplifier 72.

In operation of my automatic volume control circuit with no signal input, the

capacitors

58, 62 and 68 charge to a potential of about volts.

Transistors

72 and 74 conduct relatively heavily to reduce the voltage on lamp 36 to a point at which the lamp is extinguished. Upon the application of an input signal to the circuit which produces more than the delay voltage at brush 46, transistor 50 is gated into conduction, discharging audio filtering capacitor 62 to ground potential. For steadystate input signals, capacitor 58 discharges with a time constant of one second to increase the lamp voltage and reduce the resistance of element 32 until the output signal from transistor 28 is attenuated sufiiciently that transistor 50 is nearly extinguished.

For pulsed input signals of a duration appreciably less than the one-second attack response time of the system, an arbitrary reduction in gain is made. This arbitrary reduction is fairly large, subject to the limitation that it not be objectionable to the listener. Accordingly the arbitrary attenuation may be of the order of magnitude of approximately 1 db which is the sensitivity of the normal human ear. It is desired that this attenuation be substantially the same irrespective of the number of pulses within a one-second period. This is achieved by making capacitor 62 large compared with audio filtering capacitor 68 in FIGURES 1 and 2, or by making capacitor 84 large compared with audio filtering capacitor 86 in FIGURES 3 and 4, and by providing diode 66 to insure that

capacitor

62 or 84 can instantaneously discharge through transistor 50 but can recharge only through the high resistance of

resistor

64, 82, 88, or 92 rather than merely through the low resistance of

resistor

60 or 80.

It will be seen that I have accomplished the objects of my invention. I have provided an automatic volume control circuit having a relatively short attack time and a relatively long release time. It is especially adapted for use in jukeboxes to permit them to play a wide variety of types and brands of record disks at substantially the same output level. My circuit minimizes the undesirable effects of sharp pulses of short duration in the output sound level. My circuit provides excellent regulation of output over a wide range of inputs.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. An automatic volume control circuit for regulating an output signal including in combination, a variable gain element providing said signal, means comprising a capacitor for controlling said element, means for charging said capacitor with a relatively long timeconstant, and means responsive to an output signal exceeding a certain value for discharging the capacitor with a relatively short time-constant, the controlling means comprising means responsive to charging of the capacitor for increasing the gain of the element and responsive to the capacitor for decreasing the gain of the element.

2. An automatic volume control circuit for regulating an output signal including in combination a variable gain element providing said signal, a first transistor having a base and an emitter and a collector, means applying said signal to the base, means for maintaining the emitter at such fixed potential that the transistor is conductive only for output signals exceeding a certain amplitude, means including a resistor of very high resistance for connecting the collector to a source of voltage, a storage capacitor, means coupling the capacitor to the collector, the transistor and the resistor comprising a groundedemitter gated amplifier, and means responsive to the voltage drop between collector and emitter of the transistor for controlling said element, the controlling means comprising means responsive to a large voltage drop for providing a high gain and responsive to a small voltage drop for providing a low gain.

3. A circuit as in claim 2 in which the controlling means comprises a second transistor having a base and an emitter, means connecting the collector of the first transistor to the base of the second transistor, and means including a resistor of appreciable resistance for con necting the emitter of the second transistor to a voltage source.

4. An automatic volume control circuit for regulating an output signal including in combination, a variable gain element providing said signal, means comprising a control capacitor for controlling said element, an auxiliary capacitor, means for charging said control capacitor and said auxiliary capacitor with a relatively long-timeconstant, and means responsive to an output signal exceeding a certain value for discharging the control capacitor with a predetermined and relatively short timeconstant and for substantially instantaneously discharging the auxiliary capacitor.

5. A circuit as in claim 4 in which said element has a response lag and in which said predetermined timeconstant is appreciably greater than said lag.

6. A circuit as in claim 4 in which said control capacitor has a much larger capacitance than said auxiliary capacitor.

7. A circuit as in claim 4 in which the charging means comprises means for charging the auxiliary capacitor from the control capacitor with a time-constant approximately the same as said predetermined time-constant.

8. A circuit as in claim 4 in which the means for discharging the control capacitor comprises a resistor 'having a relatively low resistance, in which the charging means for the control capacitor comprises a resistor having a relatively high resistance, and in which the charging means for the auxiliary capacitor comprises a resistor of intermediate resistance coupling the control capacitor and the auxiliary capacitor.

9. A circuit as in claim 4 in which said signal responsive means comprises a device providing a very low impedance in response to an output signal exceeding such value and means including a rectifier for shunting said device across said auxiliary capacitor.

10. An automatic volume control circuit for regulating an alternating-current output signal including in combination, a variable gain element providing said signal, means including a control capacitor having a relatively large capacitance for controlling said element, a first auxiliary capacitor having a relatively low capacitance, a second auxiliary capacitor of intermediate capacitance, means including a first resistor having a relatively large resistance for charging the control capacitor, a device providing a very low impedance in responseto an output signal exceeding a certain value, means including said device and a second resistor having a relatively low resistance for discharging the control capacitor, means including a third resistor of intermediate resistance for charging the second auxiliary capacitor from the control capacitor, means including said device and a rectifier for discharging the second auxiliary capacitor, and means including the first of the auxiliary capacitors for providing a capacitive shunt across the device.

11. A circuit a-s in claim 10 in which the second resistor provides a certain time-constant for the discharge of the control capacitor and in which the second auxiliary capacitor is charged With approximately the same timeconstant.

12. A circuit as in claim 10 in which thte second auxiliary capacitor is charged through the second and third resistors in series.

13. A circuit as in claim 10 in which the device is capacitively shunted by the auxiliary capacitors in series.

14. A circuit as in claim 10 in which the second auxiliary capacitor is charged through only the third of the resistors,

15. A circuit as in claim 10 in which the device is capacitively shunted by only the first of the auxiliary capacitors.

References Cited UNITED STATES PATENTS 2,957,074 10/1960 Trevor 325-415 X 2,958,027 10/1960 Moseley et al 320-1 X 3,021,489 2/1962 Nielsen 330-141 X 3,109,989 11/1963 Muir 325-415 X 3,110,864 11/1963 Smith-Vaniz et al. 325-411 X 3,165,699 l/1965 Henmueller 325-411 X 3,333,208 7/1967 Hudak 330-141 X LEE T. HIX, Primary Examiner A. D. PELLINEN, Assistant Examiner U.S. Cl. X.R.