US2320429A - Signal recording and reproducing system - Google Patents

Description

June l,v 1943' H. J. HAsBRoUcK, JR 2,320,429

SIGNAL RECORDING AND REPRODUCING SYSTEM Filed Aug. 20, 1940 "QQ"Y 12% f l y .a/mf .alim @070' Patented lJune 1, 1943 2.320.429 SIGNAL RECORDING AND REPRODUCING SYSTEM Harold J. Hasbrouck, Jr., Merchantvlle, N. J assignor to Radio Corporation of America, a torporation of Delaware i Application August 20, 1940, Serial No.I 353,340

2 Claims.

This invention relates to signal recording and reproducing systems, and more particularly to a system wherein the linear speed of the record relative to the scanning element varies with the playing time.

It is well known that in certain types of phonographic apparatus such, for example, as the conventional phonographs employing disc records which rotate at constant angular velocity, the linear speed of the record relative to the pickup varies in accordance with the radial position of the pickup on the record. In systems of this type, it has been found that loss of high frequencies occur at the low linear speeds obtained on the inner grooves, and this is particularly true in the case of records which operate at slow speed, such as 33% R. P. M. for example.

Various proposals have heretofore been made ormaking the effective response at higher frequencies relative to that at lower frequencies greater when the recording or the reproducing stylus, as the case may be, is in one part of the sound track than when it is in another part of the sound track. An example of such a proposal may be found in the British patent to Barrett, No. 443,801. However, the network proposed by Barrett and other similar networks of the prior art have the disadvantage of attenuating the overall response of the amplifier, which is an undesirable feature.

I The primary object of my present invention is to provide an improved method of and system for recording signals upon and reproducing signals from a record disc which varies in linear speed in the manner previously mentioned, which method and system will be entirely free from the aforementioned difficulties.

More particularly, it is an object of my present invention to provide an improved method of and system for recording signals on and/or repro- In accordance with my present invention, I employv a, feedback amplier in connection with the cutter by means of which the recording is made and automatically compensate for the high frequency losses by` varying the amplifier feedback. The particular amplifier employed makes use of negative feedback which is varied as the recording progresses, and preferably only the feedback at the higher frequencies is varied, the gain of the amplier otherwise remaining constant. A variation in the feedback may be obtained by varying the cathode by-pass capacity in the feedback circuit by means of a tapped condenser or a plurality of separate condensers under control of the cutter head as it moves radially across the record. Preferably, the condenser taps are located adjacent the moving carriage of the recorder head and connection is -made thereto by a sliding arm connected to the recorder head` In this manner, the high frequency response of the recording amplifier is changed in accordance with the radial position of the cutter head as it passes over the record.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as toits organizationwand method of operation, as well as additional` objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawing in which Figure 1 is a diagrammatic illustration of a phonograph employing a disc record and of 1an -amplier circuit used therewith in accordance with my present invention, and

tem illustrated in Fig. 1 showing the effect of varying the cathode by-pass capacitor in the ducing signals from a record as aforementioned whereby distortion normally resulting from variation in linear speed of the record relative to the signal translating device associated therewith is eliminated. l

Another object of my present invention is to provide an improved system and method as aforesaid which is particularly useful in record- `ing sound upon a disc record with the ald of an electrical amplifier and which will not attenuate the overall response 'of the amplier.

' A further object of my present invention is to provide an improved recording system as aforesaid'which is'simple in construction and highly efllcent in use.

feedback circuit of the amplifier.

Referring more particularly to the drawing, wherein similar reference numerals indicate corresponding parts throughout, there is shown, in

y Fig. 1, a preamplifier I which may be fed from e suitable source of signal energy,` and which is coupled through an amplier 3 to a power ampller 5, the power amplifier 5 being connected to a suitable load through the transformer 1. Connected to a tap on the secondary winding of the output transformerl through a lead 9 is a resistor Il in the cathode circuit of the amplifier 3, one end ofthe resistor II and one end of the secondary winding of the transformer I being each connected to ground to complete the feedback circuit or path which develops feedback voltages across the resistor II.

Mounted upon a conventional turntable for rotation therewith in well known manner is a record disc R' over which extends a frame I3 which rotatably carries a lead screw I5 arranged to feed a signal translating device, such as a cutter head I1, substantially radially across the record R, the output transformer 1 being connected to the cutter head I1 for applying signal voltages to the latter. The cutter head l1 is carried by a carriage I9 to which may be secured a slider 2l adapted t0 successively contact the terminals 23a, 25a, 21a, 29a, and 3Ia, of a plurality of capacitors 23, 25, 21, 29 and 3l, respectively, the capacitors 23, 25, 21, 29 and 3i each having a different value and progressively increasing in capacity from the capacitor 23 to the capacitor 3I. The common terminal of the several capacitors is connected through a lead 33 to the cathode' end of the resistor I I, and their respective terminals 23a, 25a, 21a, 29a, and 3Ia are connected to ground through the slider 2 I, the conductive carriage I9, the conductive frame I3. the lead 35 and the lead 31.

It will be obvious, from the foregoing description, that the slider 2| successively makes contact with the terminals 23a, 25a, 21a, 29a, and 3Ia as the cutter head I1 moves radially across the record R in response to the lead screw I5 to thereby successively shunt the capacitors 23, 25, 21, 29 and 3I across the cathode resistor II. In this way, the effective impedance ofthe resistor II, and therefore the frequency response characteristic of the feedback circuit, is variably altered. The feedback circuit is preferably of the negative type and is designed to attenuate the high frequency response, and the values 0f the capacitors 23, 2.5, 21, 29 and 3l are so chosen that the high frequency response will be increased relative to the low frequency response when the cutter I1 is in a region adjacent the center of the record than when it is near the periphery thereof. Only the feedback at high frequencies is varied, the gain of the amplifier otherwise remaining constant. The resulting response characteristic is shown by the series of curves in Fig. 2 wherein the frequency is plotted against the change in amplifier gain in db. resulting from each of the capacitors 23, 25, 21, 29 and 3|. Assuming that these capacitors have the values 0.0185 mf., 0.012`

mf., 0.0075 mf., 0.0055 mf. and 0.0035 mf., respectively, it will be seen, from Fig. 2, that the capacitor 23, which is operative nearest the record center, produces the greatest change in amplifier gain at from about 3000 cycles to 10,000 cycles, the capacitor 25, which is operative at a greater radial distance from the record center, produces a somewhat smaller change in amplifier gain in the same spectrum, and so on until the capacitor 3| is reached, the latter being operative in the peripheral region of the record and producing substantially no increase in amplifier gain in this spectrum.

Near the periphery of the record, it is desirable that the successive capacitors' be shunted across the .cathode resistor II for a relatively longer period than preceding capacitors, since A the rate of change of high frequency loss is less adjacent the record periphery than adjacent the center thereof. For this reason, the terminals 23a, 25a, 21a, 29a and 3Ia are made successively longer, as clearly shown in Fig. `1.

Although I have shown and described but one embodiment of my invention, it will be apparent to those skilled in the art that many other modifications thereof are possible. have shown and described my invention in connection with a recording system, it will be equally apparent that the invention may be used in a reproducing system as well, in which case, the cutter I1 would be replaced by a pickup device which would serve as the input to the preamplifier I and the output transformer 1 would be connected to a suitable loudspeaker or the like. Furthermore, instead of employing the system for recording from adjacent the center of the record outwardly toward the periphery thereof, as shownI by the arrow A in Fig. 1, it may be used equally well for recording from the periphery of the record toward the center. Various other changes will, no doubt, readily suggest themselves to those skilled in the art. I, therefore, desire that my invention shall not be limited except insofar as is made necessary by the prior art vand by the spirit of the appended claims. I claim as my invention:

vl. In electrical recording apparatus, the' combination of a 'cutter adapted to be moved substants'ally radially across a rotatable record disc, a recording amplifier coupled to said cutter for applying signal voltages thereto, means providing a feedback path for said amplifier, said means including a resistor across which feedback voltages are developed, and variable capacity means in shunt with said resistor for controlling the frequency response characteristic of said feedback path, said last.y named means being variable in accordance with the radial position of said devic relative to the record, and means responsive to movement of said cutter across the record for varying said capacitor meansl progressively in value and for progressively varying time intervals as said cutter moves across the record.

2. In electrical recording apparatus, the combination of a cutter adapted to be moved substantially radially across a rotatable record disk, a recording amplifier coupled to said cutter for applying signal voltages thereto, means providing a feedback path for said ampliensaid means including a resistor across which feedback voltl' ages are'developed, variable capacity means in shunt with said resistor for controlling the frelquency response characteristic of said feedback path,'said last named means comprising a piurality of shunt related capacitors of different values each having a common terminal at one -end of said resistor, and a sliderl associated with said cutter and adapted to successively engage the other terminals of saidvcapacitors as said cutter moves across therecord,I said slider having connection with the other endof said resistor, and said other capacitor terminals being so constructed and arranged that are maintained in shunt with said resistor for'a longer period than preceding capacitors as said n cutter moves radially outwardly of the record.

HAROLD J. HASBROUCK, JR.

Also, although I successive capacitors

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