US2065344A - Control means for signal control transmission systems - Google Patents

Description

Dec. 22, 1936. H. D. NEWTON 2,065,344

' CONTROL MEANS FOR SIGNAL CONTROL TRANSMISSION SYSTEMS Filed Feb. 1, 1933 4 K E w E E {:1

m0 300 700 /000 2500 3000 CYCLES Ff SECUIVD I MlPl/T 1E if 24 25 Inventor.- Harold Dnewton.

H is Attorngy.

Patented Dec. 22, 1936 UNITED STATES PATENT- OFFICE CONTROL MEANS FOR SIGNAL CONTROL TRANSMISSION SYSTEMS Harold D. Newton, Westmont, N. J., assignor to General Electric Company, a corporation of New York Application February 1, 1933, Serial No. 654,643 8 Claims. (01. 179-1) The present invention relates to means for quency response characteristic of said system varying the frequency response characteristic of may be varied between wide limits and by a single an electric signal transmission system, whereby control means.

- signals'transmitted therethrough may be attenu- It is a common characteristic of known freated Within desired and variable frequency quency response control systems, that attenuation 5 rangeg of or change in the frequency response character- Means for varying the frequency response istic of the system is accompanied by a change in characteristic of signal transmission systems are the apparent overall output volume as registered well known and at present are applied generally by the listening ear. In certain other cases, there 10 to audio frequency amplifiers as tone control may be an actual change in the amplitude of the 10 means adapted to accentuate the amplification signals transmitted through the system to which in selected portions of the audio frequency rethe tone control means is applied, as the tone sponse range of such amplifiers. For this reason control means is varied. For example, certain the present invention will be herein described by known forms of tone control means having a tone Way of example, more particularly in its applicacontrol adjustment whereby the high frequency tion to audio frequency amplifiers, although it end of the audio frequency range is attenuated is not necessarily limited thereto. to a greater extent than the middle and lower fre- In the usual audio frequency amplifying sysquency ranges, provided also a noticeable accomtem, the tone control means include circuit net panying reduction in the apparent volume of the s works and circuit elements therein for eifecting signal as reproduced by a suitable output device. within limits a, desired change in, or adjustment It has been found, however, that a frequency of, the sound frequency transmission or audio freresponse control system embodying the invention,

' quency response. characteristics of the system, substantially entirely obviates the above dewhereby the electrical or sound output therefrom scribed undesirable characteristics of tone conmay be modified in accordance with a predetertrol means heretofore employed, whereby the fre- '25 mined frequency response characteristic curve quency response characteristic of the system to to produce a pleasing tone quality from a suitable which it is applied may be Va d Without appreoutput device. ciably affecting the overall amplitude of signal In radio receiving apparatus, the tone control waves transmitted through said system. arrangement in connection with an audio fre- In accordance Wi h t e invention, a W de ran e 30 quency amplifier is such that the audio frequency of tone control is obtained by providing in consignals from a sound producing device, such as nection with an audio frequency transmission a loud speaker, for example, are increased or decircuit or channel, means providing shunt paths creased within certain portions of the audio frehaving impedance values so related to each other 5 quency range, whereby the reproduced sound and to that of said transmission circuit or chanmay be made pleasing to the ear under various nel, that each is adapted to attenuate signals in conditions of reception. v a selected audio frequency range, with substan- Tone control systems heretofore employed in tially equal individual shunting effect on the cirradio receiving apparatus and the like are characcult, and by providing a control means having 40 terized by the fact that only a limited range of substantially no frequency response character- 40 operation is usually obtainable, or when arranged. istic arranged to increase gradually the controlfor a wide range of audio frequency tone coinling effect of the one shunt path while decreasing pensation, require a plurality of control devices. the controlling effect of the other.

It is, therefore, a primary object of this in- By properly relating the circuit impedance vention to provide an improved frequency responvalues of the controlling means, the transmission sive tone control system having a relatively wide circuit and the attenuating means, it has been range of control. It is a further object of this found that the control may be effected throughout invention to provide an improved audio frequency the frequency range with substantially constant tone control system which embodies a simple cirsignal amplitude or constant volume of the sound m cult and a minimum number of circuit elements, output. 1 and which may be applied to existing signal The novel features which are considered chartransmission systems at low cost. acteristic of the invention are set forth with par- It is a still further object of the present in ticularity in the appended claims. The invention vention to provide an improved control circuit itself, however, both as to its organization and 5 for a signal transmission system, whereby the freits method of operation, together with additional objects and advantages thereof, will best be understood from the following description taken in connection with the accompanying drawing, in which:

Figure 1 is a circuit diagram showing a portion of the signal transmission circuit of an audio frequency amplifier provided with a tone control system embodying the invention; Fig. 2 shows curves illustrating certain operating characteristics of the amplifier shown in Fig. 1; Fig. 3 is a circuit diagram'showing a modification of the tone control system of Fig. 1; and Fig. 4 shows a detail modification of the circuit shown in Fig. 3.

Referring to Fig. 1, an electron discharge amplifier device I is coupled to a suitable source of audio frequency currents represented by a suitable input transformer 2. The electron discharge device I is connected to a second electrorr discharge amplifier device 3 through a suitable signal transmission circuit, which in the present example includes an audio frequency interstage coupling transformer 4, having an output lead 5 which is connected to thegrid of the electron discharge device 3, and a return lead 6 which is connected to the cathode of the electron discharge device 3 through a by-pass capacitor I. The grid of the electron discharge device 3 is biased by a potential derived from a suitable source such as a resistor 8. An output choke coil I0 and a coupling capacitor 9 are arranged in the output or anode circuit of the device 3 to supply output signals to a suitable translating device such as a loudspeaker ll. Any suitable output circuit may however be employed to couple the tube 3 to the loudspeaker. The loudspeaker ll represents any suitable sound producing device which may be connected in the output circuit of the discharge device 3 for receiving the signals and for con-. verting them into audible sounds. In the present example, audio frequency signalssupplied by the input device 2 are amplified by the electron discharge device I and are transmitted through the transformer 4 and the transmission circuit 5, 6 to the electron discharge device 3.

Connected in shunt with the signal transmission circuit 5-6 is a circuit network, or tone control system, including means for variably attenuating a portion of the frequency range of signals to be transmitted by said circuit. In the present example this includes an impedance device l2, the impedance of which varies with the frequency of the applied currents, and which may comprise a fixed capacitor having low capacity connected with the transmission circuit, preferably at the high potential side 5, and a .series variable resistance provided by a potentiometer iii, the movable contact l4 of which is preferably connected with the low potential side 6 of the transmission circuit, all as indicated.

It will be seen that variation of the series resistance by operating the movable arm or contact l4 along the resistor element of the potentiometer l3 will cause the effectiveness of the impedance device or shunt capacity provided by the condenser I2, to be varied. When the movable contact I4 is moved to a position adjacent to or at one terminal to which the capacitor I2 is connected, it will be seen that the latter. is most effective in providing a shunt path across the transmission circuit and serves to attenuate signals above a certain predetermined frequency depending upon its capacity value and its relative shunt impedance value in the circuit 5-6.

The capacitor l2 may have a capacitance such that its impedance to higher audio frequency signals is relatively low with respect to that of the transmission circuit impedance within that range, and the potentiometer l3 or its equivalent resistance, may have a maximum impedance value such that when fully in circuit with the capacitor l2, the effectiveness of the latter as a circuit shunting means is substantially nil. The network or system whereby a desired change in the tone or frequency transmission characteristic of a circuit without appreciably changing the resistance load of the transmission circuit, or the volume or amplitude of the signals transmitted therethrough may be effected is completed by an impedance, in the present example, an inductor l5, connected in shunt across the signal transmission circuit 56, also through the potentiometer means l3, and, through said poten tiometer means, in shunt also with the reactancc device l2. The effect of this circuit arrangement is to provide a substantially constant shunt re- 7 sistance load, but having an adjustable impedance, across the signal transmission circuit 5-6 at all times.

The tone control means or circuit thus provided operates to attenuate signals in the higher frequency range when the adjustable contact 14 of the potentiometer is moved toward the left in the direction of the capacitor [2, and operates to attenuate signals in the lower frequency range when the contact I4 is moved toward the right in the direction of the inductor l5; while in the intermediate positions substantially equal parallel paths are provided which attenuate only in some degree signals in both the high and low frequency ranges. The attenuation of the high or low frequency signals is due to the change in the effectiveness of the shunt impedance l5 and the capacitor [2 when the potentiometer arm I4 is shifted to the right or left of the intermediate position.

This tone control means or network may be connected across either of the windings of the transformer 4 by properly proportioning the component parts thereof in accordance with-the circuit in which it is to be used. The tone control means now includes a circuit providing a high frequency path and a low frequency path connected together by an element having no frequency characteristic. The impedance values in each shunt path are preferably such that each path provides the same resistance load on the transmission circuit whereby thechange from the one to the other by operation of the potentiometer device l3 produces no appreciable change in the overall apparent output volume of signals delivered from the system. The resistance of the potentiometer I3 is of a value which permits but a slight amplitude reduction in the normal frequency characteristic of the transformer or signal channel when the adjustable contact I5 is at the midpoint on the potentiometer l3.

Reference may now be made to Fig. 2 which shows a response curve in which per cent of response is plotted against frequency in cycles per second. Curve A illustrates the frequency characteristic of the amplifier shown in Fig. 1 as measured across the circuit 55 of the secondary winding of the transformer 4 without the tone control means. Curve B shows the attenuation of the treble or high frequency signals when the potentiometer arm I4 is at the left extremity of therein may return to the device l8. Audio frequency signals are applied to device I8 through a suitable input or coupling device 20 and the output of transmission circuit l6l1 is connected with output translating device 2| through a suitable coupling device 22.

In the present example, audio frequency signals applied through the transformer 20 are amplified by the electron discharge device l8 and are transmitted to the translating device 2| through the transmission circuit |6-l1 and the coupling device 22. Any suitable audio frequency response means may be connected to the transformer 22 such as a sound producing device 2| shown in connection with said transformer for receiving the signal output from the transmission circuit Iii-I1 and for converting the same into audible sounds. This device may be preceded by any desired degree of amplification, as is well understood. Further description of the amplifier circuit is believed to be unnecessary as it represents any suitable signal transmission circuit and is included in an audio frequency amplifier only by way of example as adaptedalso to this modification of the invention.

'I'h'esignal transmission circuit l8-I| is provided with a tone control network or means including an impedance device 23, the impedance of which varies with the frequency of the applied currents and a second impedance member 24 having no frequency characteristic, all connected with one side of the transmission circuit I 6, and a potentiometer 25 arranged therebetween and having a movable contact 26 connected to the other side of the transmission circuit l1. As the movable contact arm 26 is moved to the right to include resistance in circuit with the attenuating device 23, it causes resistance to be removed from circuit with the resistor 24 until finally .the resistor 24 is connected in shunt with the transmission circuit Iii-l1 and the attenuating device 23 is rendered ineffective. Likewise, when the potentiometer arm is moved to the left to the opposite position at the other extreme end of the potentiometer element the resistor 24 is rendered substantially ineffective as a shunt means across the circuit while the device 23 is fully effective. The resistor M is of such a value that it may provide across the circuit iii-ll substantially the same shunt impedance at allfrequencies in the range to be transmitted, as does the device 23 in the range of frequencies to be attenuated The effect of this circuit arrangement is to provide substantially a constant impedance in shunt across the signal transmission circuit for all positions of the adjustable tone control means, by reason of the fact that the variable resistor M is substituted at one end of the control range for the 18, the lead 16 being the paths singly, such paths being composed of the impedance devices 23 and 24 and portions in circuit therewith of the. resistance element of the potentiometer element 24.

In order that the signal potential output through the transmission circuit Hi-l1 may be made substantially constant, or the apparent out-, put volume may be substantially constant, as determined by listening to the output of the sound producing device 2 I, or be made to vary from such constant output in any desired way, or by way of correction of certain undesired responsecharacteristics, the resistor 24 is made variable, whereby its impedance value may be changed or adjusted with respect to that of the device 23.

With a variable control means of this character, the tone of the output may bevaried by adjustment of the contact 26, and the effect of such tone adjustment upon. the volume or the apparent volume, as measured by listening to the sound producing device 2|, may be, adjusted by adjustment of the resistor 24. The resistor 24 may be fixed when once adjusted to a desired value, as determined by measuring the'amplitude of the signal response in circuit l6- -l'1 or by listening to or measuring the output of the sound producing device 2 I.

The resistor is adjusted to a value such that asan impedance device in the signal transmission circuit it is substantially equal to the reactance device in the frequency range for which the reactance device is effective as an attenuating means. The potentiometer is of such total re- 'sistance value that by its operation, sufficient resistance may be inserted in .circuit with the reaudio frequency transmission circuit. Likewise,

the tone control system shown may be followed by amplifying means other than the sound producing device 2|.

- In connection with the attenuation of signals at frequencies in other ranges, any suitable impedance means may be inserted in place of device 23 of Fig. 3. For example, referring to Fig. 4{ a choke coil or impedance 2! may be substituted, with or without other change in the circuit. In the present example, no other change is made and the impedance device is connected in circuit with the potentiometer 25 in the same manner as the capacitor 23 in Fig. 3. In this case, however, as

is obvious, the choke coil provides a relatively high impedance at the upper or high frequency end of the audio frequency range and a decreasingly lower impedance toward the lower end of the range. Accordingly, when connected by operation of the control contact 26, whereby it is most effective across the circuit lit-ll, it serves to attenuate the lower frequency end of the audio frequency range.

From the foregoing description it will be seen that in accordance with the invention, and as a preferred embodiment thereof, a tone control system embodying the invention includes a reactance device or circuit impedance devic-e having an impedance which varies with variations in the frequency of currents which are caused to pass through it, and such device is connected with a signal transmission channel substantially in parallel with a second impedance device. The effective impedance values reduced to terms of load resistances are equal but in different frequency ranges whereby they are controllable by a common potentiometer means having no frequency characteristic, thereby maintaining substantially a constant load on the signal transmission circuit.

My invention provides a tone control for accentuating the amplification of any selected range of frequencies with substantially constant. load and volume output therefore irrespective of the adjustment of the control.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentalities employed, may be made without departing from the spirit and scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a signal transmission circuit, means to transmit through said circuit audio currents extending over a wide range including high audio tones and low audio tones, a tone control network effective over said wide range and predominately effective in the ranges of said high and low tones, said network comprising a resistance, one point of said resistance being connected to one side of said circuit through an impedance which is high to low tones andlow to high tones, and another point on said resistance being connected to the same side of said circuit through an impedance which is low to low tones and high to high tones, and a connection from the other side of said circuit to a point on said resistance variable between said first points whereby as said connection is varied along said resistance opposite effects are produced upon said high and low tones.

2. In combination, a signal transmission circuit, means to transmit through said circuit audio currents extending over a wide range including high audio tones and low audio tones, atone control network effective over said wide range and predominately effective in the ranges of said high and low tones, said network comprising a resistance, one point of said resistance being connected to one side of said circuit through a capacitance having high impedance to said low tones and low impedance to said high tones and another point on said resistance being connected to the same side of said circuit through aninductance having low impedance to said low tones and high impedance to said high tones, both said inductance and capacitance having values of impedance varying oppositely with respect to frequency in said frequency range between said high and low tones, and a connection from the other side of said circuit to a point on saidresistance variable between said first points whereby as said connection is varied along said resistance the frequency attenuation characteristic of said circuit is correspondingly varied, said variation occurring throughout said range and in opposite senses with respect to frequency.

3. The combination with an audio frequency transmission circuit, of a tone control network connected thereto, said network including a resistor potentiometer having a movable contact, a frequency responsive impedancedevice connected between one end of said potentiometer and one side of said circuit, a second impedance connected between the other end of said potentiometer and the same side of said circuit, and means connecting said movable contact of said potentiometer and said impedances to the opposite side of said circuit, said impedances being of such character that said potentiometer operates as a variable control means for said tone control network while maintaining the effective ohmic load of said network substantially constant.

4. An audio frequency signal transmission circuit including input and output circuits, a tone control circuit connected across one of said circuitsfor by-passing selected audio frequency energy including an inductive reactance in one path, a capacitive reactance in another path, and a potentiometer having a single movable contact arranged for selectively proportioning the effectiveness of said paths in accordance with the position of the single movable contact of said potentiometer thereby operates selectively to attenuate the signals in different frequency ranges dependent upon the position of said single movable contact while maintaining a constant ohmic load upon said transmission circuit.

5. The combination with an audio frequency current transmission circuit of a tone control network connected in shunt thereto, said network including a resistor potentiometer having a movable contact connected to one side of said circuit, a frequency responsive impedance device connected to one end of said potentiometer, a second impedance device having a resistance value equal to said first impedance and being connected to the other end of said potentiometer, both of said impedances being connected to the other side of said circuit, said impedance devices having different impedance frequency characteristics and cooperating with said potentiometer to maintain the total apparent volume of audio frequency current transmitted substantially constant for all of positions of said potentiometercontact.

6; The combination with an audio frequency transmission circuit having a sound producing device, of a tone control network connected thereto, said network including a resistor potentiometer having a movable contact, a frequency responsive impedance device connected between one end of said potentiometer and one side of said circuit, a second impedance having substantially the same ohmic resistance as said first impedance device and being connected between the other end of said potentiometer and said one side of said circuit, and means connecting said movable contact of the potentiometer to the other side of said circuit whereby the potentiometer operates as a variable control means for said tone control network and said impedances cooperate to maintain the apparent volume of said sound reproducing device substantially constant for all'adjustments of said potentiometer contact.

7. The combination, in a circuit for transmission of currents representing music, of a tone control network comprising a plurality of im pedances including a resistor and a pair of impedances having different frequency characteristics, one terminal of each of said impedances being connected to one side of said circuit and the opposite terminals of said impedances being connected respectively to opposite ends of said resistor, and a connection from a variable point on said resistor to the opposite side of said circuit, said impedances being of such character that as said variable point is moved along said reproduced currents is maintained substantially constant.

8. The combination, in a circuit for transmission of currents representing music, of a tone control network comprising a plurality of impedances including a resistor, and a pair of impedances having difierent frequency characteristics, one terminal of each of said impedances being connected to one side of said circuit and 5 the opposite terminals of said impedances being connected to opposite ends of said resistor, a connection from a variable point on said resistor to the opposite side of said circuit, said impedances being of such character that as said variable point is moved along said resistor the tones efficiently transmitted through said circuit are varied while the total volume of reproduced cur- I rents is maintained substantially constant, and

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