US2515111A - Electronic fade-in control system for phonographic reproduction or the like - Google Patents

Description

July 11, 1950 J. w. BUcHHoLzER Erm.

ELECTRONIC FADE-IN CONTROL SYSTEM F' PHONOGRAPHIC REPRODUCTION OR THE LIKE Filed oet. 4, 194e ATTORNEYS Patented July ll, 195i() UNITED STATES PATENT OFFICEI ELECTRONIC FADE-IN CONTROL SYSTEM FOR PHONOGRAPHIC REPRODUCTION OR THE LIKE of Ohio Application October 4, 1946, Serial No. 701,130

Claims.

The present invention relates to a system for the electronic reproduction of sound generated by the usual phonograph disk and is designed to improve upon such systems so as to eliminate certain objectionable features ordinarily present when sound thus generated is transmitted to and reproduced over standard amplifier circuits.

While the invention has a wide range of utility and may be used for many purposes, the use to which the invention has been especially adapted is in the reproduction of records of organ or vocal music such as often played during funerals or other events where it is desirable to reproduce the records without the customary objectionable noises which have heretofore been necessarily present.

One of the objects of the invention is the elimination of the initial surface noise which is heard in phonographic reproductions as the needle travels over the spiral or lead-in portion of the sound track at the start of the reproduction. This is an important element of the system as the reproductions, especially at funerals, are conducted while the room is very still and every discordant sound is highly magnified to the ears of the auditors and unless the initial surface noise is entirely suppressed, the effect upon the auditors is very objectionable. The surface noise produced by the needle before it reaches the actual sound portion of the track will vary in intensity according to the material of the record or the extent to which it has been worn, and it is, therel fore, one of the achievements of the present invention that however strong these noises may be they are completely suppressed so that no sound is reproduced until the needle reaches the first note of modulation on the record.

The principle upon which the first object of the invention is based is that the signals produced by the surface noises, although to the ear they may seem to be intense, are, in fact, relatively weak and in all practical cases are weaker than any sounds reproduced by the musical modulations. The system, therefore, provides a means which blocks off the passing of weak signals such as would be produced by surface sounds, but will clear at the first musical note.

Another object of the invention is to avoid a sudden transition from complete silence to the reproduction of musical sounds. If the musical notes were instantly produced at their full intensity, the impression would be highly objectionable. It is, therefore, one of the purposes of the invention to provide means by which the musical notes, as soonas they appear, are automatically faded in from zero to the predetermined volume which is controlled by the gain setting of the audio system.

The accomplishment of the above specified objects creates a further condition which the present invention intends to rectify'. It frequently happens that a pause or hiatus will occur inthe flow of musical tones in a composition or vocal piece. At such a time occurring during the reproduction of the music, it is not desired that the musical notes again fade in, but that they should resume immediately at the full intensity determined by the setting of the audio system. The system which has been created, therefore, includes what may be termed a time delay which may be set at any suitable point so that operation of the fade-in is circumvented without interfering with passing the conventional audio signals through the amplifier. The duration of the time delay is selected so as to take care of the longest hiatus which may normally occur in selected records or compositions.

During such pauses as may occur when it is desirable to have the time delay function, the surface noises may appear, but the pauses are ordinarily of slight duration so that the ear does not catch them.

At the end of the musical notes, the blocking off of the surface noises will again take place and the complete reproduction will, therefore, be a perfect simulation of an actual musical performance without the objectionable noises which are usually present.

The invention is employed as an addition to any of the usual or well known audio amplifier circuits and is interposed between the phonographic reproducer and the amplifier circuit. Itv

is not necessary to illustrate the amplifier circuit which is employed, as any well known arrangement may be adapted to the combination.

The drawing accompanying this application shows a control circuit which has been perfected.

way departing from the basic principles of the invention. On the drawings appear many gures which give values for resistances, condensers and ferred to herein as they give cellent results the like, and these have been nc and are reand will serve as a guide to one see ing to employ the invention, but they are not to be taken asv to the signal grid II of the tube I.

vvoltage is rectified. element 31| of the tube 30 delivers a negative controlling. On the drawings also appear certain designations by which standard electronic units are known in the art, and these are given for the same purpose and with the same reservations.

Referring to the drawing and with particular i reference to the means employed for suppressing the mechanical sounds which are caused by the tracking of the needle before the rst note of modulation on the disk: v

What is known in this art as a 1612 tube, indicated at I, serves as a conventional input amplier tube to anyA standard audio ampliiier circuit through the lead 2. This tube is ,blocked 01T from passing a weak signal, such as is generated by the scratching noise from the needle, by v a negative charge delivered to the control grid of the tube indicated at 3. This negative charge enters the system from a C-power supply at il, thence through a 1 megohm resistor, through a switch 6 controlled by the relay l. The negative charge is conducted by the line 8 through an additional 1 megohm resistor 9 tothe grid 3.

` As the voltage supply passing to the grid 3 is l I3ab and I3b are shielded by a casing I4 from the receptacle I2 to the points where they enter the system.

As shown in the drawing, the line I3a contains two 250M resistors I5 to ground. Between these resistors I5 is connected a line IG which is, in turn, connected through a .05 coupling condenser The line I3b is connected through a 100M resistor II and a condenser I'Ib to the grid I8 of the rst triode section of a standard type 6SN7 tube indicated at 20. The plate opposed to the grid I8 is indi-- cated at I9. It will thus be seen that as soon as a signal appears at the #4 terminal of the receptacle I2, it is simultaneously transmitted to the grids II and I8; The tube 2l)Y is cascaded, asv

shown in the drawing, to provide two stages of Y resistance-Coupled audio. The gain into the second section of this tube 2U is controlledA by a variable 750M resistor indicated at 22;

As shown in the drawings, the resistor 22 is :connected to the grid 24` of the second triode section of the tube 2D. The plates I9 and 2,5 are connected to the B+ power line 28 through through a condenser 2 into one cathode 29 of a type 61-16 tube 30 in which the audio frequency The corresponding plate voltage to the line 33 which, in turn, delivers it to a switch terminal 31 and by the switch, to

be described, to the three condensers 35 arranged in parallel and connected to three terminals 36a,

361? and 35C of the variable time delay switch The 6J5 tube 45 is so biased that when there is no voltage (signal) appearing at the grid 33, the plate element 46 draws 6 milliamperes. The relay 1 heretofore referred to is connected in series with the plate 56, and when this amount of current, or slightly less, flows through the relay coil, the coil is sufficiently energized to close the switch 5. Closing the switch closes the circuit of the C-power supply which, as explained above, causes the negative charge to appear at the grid 3, suppressing any audio signal which may be transmitted to the grid and thus eiectively shutting olf the transmission ci any signal from the tube I to the further elements of the'audio amplifier.

As long as the signal received at the grids II and I 3 is weak, as is characteristic of surface noise, it is insuicient to increase the bias at grid 39 of the tube i5 and, therefore, the switch 5 remains closed and the negative charge delivered by the line 8 and appearing at grid 3 suppresses the audio signal (surface noise) ap'- pearing` at gridl II. When, however, the needle reaches the modulated portion of the groove on the record, the signal isv suiiiciently strong so that, passedby the tube 2o and ampliiied and rectified as explained, it appears as a negative voltage at the grid 39 of the tube All). As soon as this negative voltage appearsV at grid 3S, the increased bias causes the current from the plate 6 to drop, and as soon as this occurs, the energy in the relay I drops to a point where the switch 6 opens. Opening of the switch breaks the circuit of the C-supply to the grid 3 andthe tube I then functions in the normal manner, passing the musical tones on to the remaining stages of the audio amplifier, by which these sounds are then reproduced and become audible.

It will be seen that the system, so far as has been described, insures that no audible sounds will be transmitted until the surface noise generated by the record is overcome by the louder musical tones. Thus is accomplished the first stated object ofy the invention, i. e., the suppression of objectionable noises caused by the scratching of the needle in thersound track prior to the rst musical. modulation thereon. Thisl also suppresses the surface noise aty the end of the record, aftery the time-delay switch has ceased to function.

For accomplishing the second object of the invention, i. e., the fade in of the musical notes so that an abrupt commencement of the musical tones-is avoided, theinstrumentality designated at 50 and entitled Fade in Speed is provided.

Between the 1 megohm resistor 5' and the 1 megohm resistor 9, there is connected to the line 3a line 52'Wh-ich is connected to one terminal 53 of the fade-in-speed control elem-ent 5t. Two additional terminals 511 and- 55 are provided and the three terminals are connected in parallel through condensers 53a, Ella and 55a to the line 51. These condensers are preferably .5 mf. paper condensers. The elem-ent 59 is provided with a rotary plate t. InV the position shown in the drawing, current diverted from the line 3 passes through the condenser 53% only, but as the' plate 60 is turned in clockwise direction the condenser capacity may be doubled"` or tripled. The line 5l is connected to the common ground.

As soon. as theC-vol-tage passes through the switch il, the condensersarefcharged, but when the main supplyl for the negative charge at grid 3 is broken by the opening ofthe switch 6, the

condensers discharge to ground throughthe resistance network indicated on the drawin-g which? permits the residual negative charge to be removed from the grid 3 gradually so that the gain in the tube I isgradually increased, thus causing the intensity of the audio signal to gradually increase from zero to the predetermined intensity.

The speed at which the sound increases is, of l course, dependent upon the capacity of the condensers, the slower the discharge rate to the ground, the slower is the fade in of the audio signal. The rotatable .plate fpermi-ts the operator `to govern the rate of fade in subject to the rated capacity of the condensers by cutting in' one, two or more.

In order to prevent the recurrence of the fade in after the musical tones have started, in the event there is a pause in the record, the device designated as Time Delay and indicated by the numeral 40 is employed. This element of the system has already been referred to.

The element normally functions only after the switch 6 has been opened. The rotary plate 6B is shown with an enlarged portion in contact with the terminal 31 which leads to the grid 39 and also in contact with all three `terminals 36a, b and c, but one, two or all three of these terminals may be cut out, depending upon the extent to which the plate is moved between the stops 6|. These condensers receive a negative charge while the musical tones are being transmitted through the tube 2U, but when this is interrupted the voltage is gradually released to the system from the condensers, maintaining the rectified negative voltage during the pauses in the musical tones of the record. This prevents the relay from actuating the switch 6 and thus preserves the circuits as they were at the start of the musicai tones. The time delay provision may be decreased or :augmented within the capacity of the condensers 35 by turning the plate lilk to cut out one or more of the condensers.

The time delay switch is also intended to have a further function. A terminal B4 is provided at the time delay switch which is connected by the line G3 directly to the negative input line between the resistor 5 and switch 6. If the plate 60 is turned counterclockwise to the fullextent permitted by the upper stop 6|, it makes contact with the terminal 64 and the terminal 3l, thus supplying a constant negative voltage to the grid 39. This causes the current from the plate 46 to drop off, which through the relay opens the switch 6 and the fade in is eliminated. rThis position of the time delay switch is used when it is desired to cut out the fade in altogether and will permit the system to pass conventional audio signals through the amplifier.

The connections which have not been described but are shown on the drawing are conventional. A standard milliammeter 12 is arranged to be plugged in to the jack 'H for the .purpose of indieating the proper attract value and release value of the relay.

Other details and modifications may be suggested to those skilled in the art.

It will be seen that a system has been provided by which the sounds generated by the playing of a record may be reproduced electronically without the transmission of the usual surface noise that precedes the musical tones. This is due to the practical application of the fact that the intensity of suchsounds is really less than the intensity of any of the musical tones, and by maintaining a negative charge fat. the grid 'fthe` 1612 tube untilsuch time as the surface noise l switch. When, however, the time delay switchY ceases to function after the termination of' the modulated tones due to the discharge from the condensers 35, the negative charge will again appear at grid 3 of the tube l and the'surface noise will -be eliminated. The period involved is usually of such short duration that the surface noise does not affect the ear as it would at'the start of the record.

The system shown and described herein is not limited to the specific purpose for which it has been described .as it may be employed in the reproduction' of broadcast transcriptions and for other duties in connection 'with electronic sound reproduction.

While, at many points in the foregoing, emphasis has been placed on the useA of the above described system in the reproduction of musical records, it will be understood that the lsystem shown herein will operate just as effectively in the caseA of a speaking record. Therefore, in the claims we have employed the term modulated to cover those portions of the record which may be either musical tones or any other tones which `are found in the record and w l1 are intended to be reproduced, thereby d inguishing fromthe surface noise which precedes the production intended to be reproduced.

What is claimed is:

1. In a system for electronic reproduc'qn of a phonographic record, said system of the type having a phonographic reproducer and an audio arnplifying system, means interposed between the phonographic reproducer and theaudio amplifying system, said means comprising a source of negative charge connected to a control grid of a tube in the amplifying system, a make and break contact in series with said source, actuating means for said contact, electronic means energized by modulated impulses from said reproducer, and

controlling said actuating means, and a delayk device to maintain said contact in open condition during a hiatus in the modulated tones.

2..In a system for electronic reproduction of a phonographic record, said system of the type having a phonographic reproducer and an audio amplifying system, means interposed between the :phonographic reproducer and the audio amplifying system, said means compr' g a source of negative charge connected to; control grid of a tube in the amplifying system, a make and break contact in said source, actuating means for said contact, electronic means energized by modulated impulses from said reproducer, and controlling said actuating means, and means operative when said contact is broken to cause a gradual increase in intensity of the transmission by the 2 audio amplifying system.

phonographic reproducer and the audio ampliphonographic records ortheV like, said system of v the type having a phonographic reproducer and an audio amplifying system, a tube connected to the phonographic reproducer and constituting a unit of an audio amplifying system, said tube having a control grid, a constant source Of negativevoltage connected to the grid, a switch in series with said source, condenser means connected to the grid and said source, actuating means'for said switch, electronic means energized by modulated impulses from said reproducer, and controlling said `actuating means, said condenser means operating to release at a predetermined rate a negative charge Afrom said grid after the switch is opened.

5. In a system for electronic reproduction of phonographic records or the like, said system of the type having a phonographic reproducer and anali-dio amplifying'system, a tube connected to the phonographic reproducer and constituting a unit of an audio lamplifying system, said tube having a control grid, a constant source of negative voltage connected to the grid, a switch in said source, condenser means connected in parallel to the grid and said source, actuating means for said switch, electronic means energized by modulated impulses from said reproducer, and controlling said actuating means, said condenser means oper.

ating to release at a predetermined rate a, nega-f tive charge from said grid after the switch is opened, and a second condensermeans connected to said electronic means and arranged to delay dissipation .of charge therefrom, whereby said actuating means is not operated during a hiatus in the modulated pulses. 6.. In asystem for electronic reproduction o phonographic records or .the like,.said system 4of the type having an .amplifier circuit, means nor! mally impressing a negative charge on the grid l of a `tube in the amplier circuit of said system suflicient rto neutralize all signals at said tube, a

`switch controlling impressment of said charge,

current-responsive actuating means for said switch, means comprising a thermionic tube with plate current controlling said actuating means and .in suiicient yamount to hold the said switch in position to retain said negative charge .on the said grid, and electronic means connected to .the

input Aof said system and .to .the `grid of said ther.-

mionic tube, and responsive to modulations in the input of said system above -a predetermined volume level to bias the grid of said thermionic tube `and thereby lower the plate current value thereof below said .suiicient amount.

7. In a system for electronic reproduction of` phonograph records or` the like, said system of the type having an .amplier circuit, means normally impressing a negative charge on the :grid of a tube in the amplifier circuit of said ksystenr sufficient to suppress all signals at said tube, a switch controlling impressment of said charge, current-responsive actuating means for said switch, a thermionic tube normally passing a current to said actuating means in sucient amount to hold the switcnin grid-charge-retain ing position, electronic means connected to the input of said system and :to-tbe grid of said thermionic tube, and responsive to modulations in the input,- oi said systemabove a predetermined volume level, to lower the valuek of the said ourrent below said sufioient amount, and means t0 retard dissipation of the said charge on the said grid on release oi the Switch..

8. In a systemfor electronic reproduction of phonograph records or thelike, said system of the type having an amplifier circuit, means normally impressing 'a negative charge on the grid of a tubein the amplifier circuit of said system suicient to suppress yall signals .at said tube, a switch controlling impressment of said charge, current-responsive actuating means for said switch, a thermionic tube normally passing a current to said actuating means in sufficient amount to hold the switch inA grid-charge-retaining position, electronic means connected to the input of said system and to the gridof said thermionic tube, and responsive to modulations in the input of said system above a. predetermined volume level, tolower the Value of said current below said suicient amount, means to retard the dissipation of the said charge on the said grid on release of the switch, and means associated with the modulation-responsive means to retard restoration of ,said current to said sufcient amount during brief interruptions to the modulations in the system.

v9. In a system for electronic reproduction of phonograph records or-the like, said system of the type having vany amplier circuit, means normally impressing a negative charge on the grid of a tube in the amplifier circuit of said system suicient to neutralize all signals at said tube, a switch controlling impressment of said charge, current-responsive actuating means for said switch, means comprising va, thermionic tube with plate current leading to said actuating means, and in sulcient amount to hold the said switch in position to retain said negative charge on the said grid, .electronic means connected to the input of said system and-to the grid of said thermionic tube, and responsive to modulations in the input oi said system above a predetermined volumelevel to bias the grid of said thermionic tube and thereby lower the plate currentthereof below said sufficient amount, and means to retard dissipation of the negative charge on the rst-mentioned grid on release of theswitch.

10. In a system for electronic reproduction of phonograph records or the like, said system oi the type having an amplifier circuit, means normally impressing a negative `charge on the grid of a tube in the amplifier circuit of said system suiicient to neutralize all signals at said tube, a switch controlling impressment of said charge, current-responsive actuating means for said switch, means comprising a thermionic tube with plate .current Vleading to said actuating means, and in sufficient amount to hold the said switch `in position to retain said negative charge .on said grid, electronic means connected to the input of said system and to the grid of said thermionic tube, and responsive to modulations in the input of said system above a predetermined volume level lto bias the grid of said thermionic tube and thereby lower the plate current thereof below said suicient amountmeans to retard dissipation of the negative .charge on thev first-mentioned grid on release of the switch, and means -associated with the modulation-responsive means to retard restoration of said current to said sufficient amount during brief interruptions to the modulations in the system.

JULIUS W. BUCHHOLZER. ROBERT B. DRABENSTOTT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,864,890 Cloud June 23, 1932 Number 10 Number

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