US 3571764 A
Description (OCR text may contain errors)
O Umted States Patent l 13,571,764
[ 72] Inventor Werner Koenigk FOREIGN PATENTS Nelhaus, 5cm, Germany 1,042,025 10/1958 Germany 1,79/13  Appl. No. 805,759 1,147,313 4/1969 Great Britain 179/1.2  Filed Mar. 10, 1969 I  patented 23 197 Primary Examiner-Herman Karl Saalbach 73 1 Assignee Grundig Elektro Mechansich 4mm"! Examiner-T vemchsansmh Attorney-Michael S. Striker Furth Bayern, Germany  Priority Mar. 13, 1968  Germany 31 P 12 90 5954-31  TONE CONTROL ARRANGEMENT WITH VOLTAGE DIVIDER, POTENTIOMETER AND TWO SERIES RESONANT CIRCUITS ABSTRACT: A tone control arrangement in which the input signal is applied to a voltage divider consisting of two resistors connected in series. The junction of the resistors forms the signal output terminal. The series combination of a first capacitor and a first inductor is connected between one terminal of the voltage divider and the resistance winding of the potentiometer. A second capacitor is connected between the other terminal of the resistance winding and the voltage divider. A second inductor magnetically linked with the first inductor by being wound upon the same core is connected between the sliding contact of the potentiometer and the junction of the resistors of the voltage divider. The arrangement is such that in both extreme positions of the sliding contact of the potentiometer, a series resonance circuit is in parallel with one of the resistors of the voltage divider.
TONE CONTROL ARRANGEMENT WllTlil VOLTAGE DWKDER, ZPOTENTIO AND TWO SERKES RESONANT CERCIUTTS BACKGROUND OF THE INVENTION The present invention resides in a tone control for the symmetric rise or fall of selected regions in a tone frequency spectrum through the application of two series resonance circuits. These series resonance circuits become connected in parallel with one or another resistor of a voltage divider, depending upon the position of the sliding contact of a potentiometer. The junction or tap connection of the voltage divider serves as the output terminal for the controlled or regulated voltage. The inductance present in the series resonance circuits is, in accordance with the present invention, preferably constructed of two coils or windings wound upon the same core. The inductance in the resonance circuit is established through either one of these inductance windings, or both windings connected in series.
Tone controls are known in the art which are designed on the basis of continuous adjustment of one or more elements or components in the form of RC (resistance-capacitance) networks.
An arrangement is also known in the art in which the attenuation of a series resonance circuit with 9 kHz. cutoffs and the operation of a so-called tone control capacitor are simultaneously varied. Such variation is accomplished through the position of a sliding contact on a potentiometer.
In another conventional tone control circuit used for low frequencies, the low frequencies are conducted over a path which includes the series circuit of an inductor and a capacitor. The low frequency signals are taken from the junction of these two components consisting of the inductor and the capacitor. By way of another or further inductor, the resulting signal taken from the junction point is conducted again to the main channel before or after regulation by means of a potentiometer.
A still further tone control is known in the art, in which a voltage divider is provided with two resistors, and the junction of these resistors or voltage divider is connected to a potentiometer so that depending upon the position of the sliding contact of the potentiometer, predetermined portions of the resistance winding of the potentiometer is connected in parallel with predetermined portions of voltage divider. At the same time, capacitors arranged in the upper and lower branches of the voltage divider are either rendered fully effected or are short circuited. As a result of this design, a symmetrical rise or fall of the low frequency or bass notes is realized in the low frequency signals to be transmitted. it is not possible to use this arrangement for the purpose of correcting the amplitude of other regions within the low frequency band.
Accordingly, it is an object of the present invention to provide tone control which yields symmetrical rise and fall of any selectively desired frequency region from a center peak. it is the object of the present invention to provide such a tone control which functions in the aforementioned manner within the tone or audiofrequency band to betransmitted.
The objects of the present invention are achieved by applying the signal to be controlled or regulated to a voltage divider consisting of two resistors. The base terminal of the voltage divider has a reference potential applied to it, whereas the junction of the two resistors of the voltage divider, constitutes the output terminal. An inductor has one terminal connected to one electrode of a capacitor which is connected to the input terminal with its other electrode. The other terminal of the inductor is connected to one end of the resistance winding of a potentiometer. The wiping contact of the potentiometer is connected to one terminal of a second inductor which is preferably wound upon the same core as the first inductor. The other terminal of the second inductor is connected to the output terminal of the circuit, which is also the junction of the resistors of the voltage divider. The other end of the resistance winding of the potentiometer is connected to one electrode of a second capacitor which has reference potential applied to it at its other electrode. The arrangement is such that in either extreme position of the wiping contact of the potentiometer, a series resonance circuit is connected in parallel with one of the resistors of the voltage divider. The consequence is that the invention enables equal boosting and cutting of the same frequencies throughout the same bandwidth.
SUMMARY OF THE INVENTION A tone control arrangement for audiofrequency signals to provide symmetrical rise or fall of preselected regions within an audiofrequency spectrum. The input signal is applied to a voltage divider consisting of two resistors connected in series. The junction or tap of the two resistors of the voltage divider forms the output terminal of the circuit. A first capacitor is connected to one input terminal of the voltage divider and, at the same time, the capacitor is connected in series with the first inductor. This first inductor is also connected to the resistance winding of a potentiometer which leads to a second capacitor through the other terminal of the resistance winding. The second capacitor terminates at the other input terminal of the voltage divider. A second inductor is connected between the junction or tap of the voltage divider and the sliding contact of the potentiometer. The two inductors are wound upon the same or identical ferromagnetic core so as to be magnetically linked. In either extreme positions of the sliding contact of the potentiometer, a series resonance circuit is connected in parallel with one of the resistors of the voltage divider.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical circuit diagram of the tone control for a predetermined frequency region, in accordance with the present invention; and
FIG. 2 is a graphical plot of the frequency response curves realized with the circuit arrangement of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, the audiofrequency signal to be regulated is applied to the input terminals l and 2 in FIG. 1. A voltage divider consisting of resistors 3 and 4 is applied or connected across the input terminals 1 and 2. The controlled or regulated signal is taken from the tap point 5 which is the junction between the resistors 3 and 4 of the voltage divider combination. The input terminal 1 is connected to one electrode of a capacitor 6. The other electrode of this capacitor is', in turn, connected to one terminal of an inductor 7. The other terminal of the inductor is connected to the winding element of a potentiometer 9. In particular, it is the terminal 11 of the winding of the potentiometer which is connected to the inductor 7. The wiper or sliding contact 10 of the potentiometer 9 is connected to an inductor 8 which is preferably wound upon the same core as the inductor 7, so that the two inductive windings represented by the inductances 7 and 8 magnetically coupled. The terminal of the inductor or winding 8 which is opposite to the terminal connected to the sliding contact 10, is
connected to the tap point 5 of the voltage divider of resistors circuit attenuates severely the output signal at its resonance frequency, on both sides of a curve which may be established from the circuit constants and the value of the resistor 4. The
.effects of the other series resonance circuit including the capacitor 6, the inductance winding 7, and the total winding resistance of the potentiometer 9, is so severely attenuated or dampened out that the effect may be neglected within the framework of the present considerations.
If, now, the sliding contact of the potentiometer 9 is located at the other extreme position of the potentiometer in which the wiping arm or contact 10 is directly in electrical contact with the terminal 11 of the potentiometer winding, then a series resonance circuit is established through the capacitor 6, and the inductances 7 and 8 connected in series with the capacitor. This resonance circuit of the capacitor 6 and inductances 7 and 8 are, at the same time, in parallel with the resistor 3 of the voltage divider. This series resonance circuit has the efiect of amplifying low frequency signals within the region of the resonance frequency of the series resonance circuit. To compute the rise and fall or dropoff on the frequency response curve referred to logarithmic scale expressed in decibels (db.), assume that the resistors 3 and 4 have ohmic values R and R respectively. Assume further that the impedance of the series resonance circuit of capacitor 13 and inductance 18, is designated by lZ,| whereas IZ,| represents the impedance of the resonance circuit consisting of the capacitance 6 and the inductances 7 and 8.
Bax d- 4 R3+ Zzl Symmetrical control or regulation of the amplitude is thus realized on both sides of the center peak, when a a. Ac-
cordingly, this condition prevails when the values of the components on the right sides of the equations, are cor- Rise a log Fall a =20 log R4+ respondingly arranged or selected.
The tone control described above, in accordance with the present invention, may be used for the purpose of correcting a number of frequency regions of the tone or audiofrequency band, by connecting in parallel a number or plurality of pairs of series resonance circuits with corresponding selected resonance frequency.
7 The tone control, in accordance with the present invention,
solves the problem in a very advantageous manner. This is due to the condition that the present invention may be economically built or constructed with a small number of components which are not complex in design. This type of construction is of particular significance in stereo amplifiers with two channels.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types de ribed above- While the invention has been illustrated and described as dividing means connected between said input terminals, said voltage dividing means being composed of two series connected resistance means having a unction located between said two resistance means; a first output terminal connected to said junction; a second output terminal connected to said second input terminal; a potentiometer means having first and second terminals and a sliding contact; first capacitor means and first inductor means connected in series between said first input terminal and said first terminal of said potentiometer; second inductor means connected between said sliding contact of said potentiometer and said first output terminal, said first capacitor means, said first inductor means, the portion of said potentiometer located between said first terminal thereof and said sliding contact, and said second inductor means forming first series resonant circuit means; second capacitor means connected between said second terminal of said potentiometer means and said second input terminal, said second capacitor means, the portion of said potentiometer located between said second terminal thereof and said sliding contact, and said second inductor means forming second series resonant circuit means, said first and second series resonant circuit means respectively boosting and cutting said discrete band of an audio frequency spectrum symmetrically about the respective center frequencies of said first and second series resonant circuit means.
2. A tone control arrangement as defined in claim 1, wherein said first and second series resonant circuit means are tuned to the same defined frequency of said discrete band of an audio frequency spectrum whereby said discrete band is boosted and cut symmetrically about the same center frequency.
3. A tone control arrangement as defined in claim 1, wherein said first series resonant circuit means have their maximum effect when said sliding contact of said potentiometer means is moved to near said first terminal of said potentiometer, and said second series resonant circuit means have their maximum effect when said sliding contact is moved to near said second terminal of said potentiometer.
4. A tone control arrangement as defined in claim 1, including common core means upon which said first and second inductor means are wound.
5. A tone control arrangement as defined in claim 1, including further pairs of said first and second series resonant circuit means tuned to other defined frequencies in said discrete band of an audio frequency spectrum.
6. A tone control arrangement as defined in claim 1, including means for applying ground potential to said second input terminal and to said second output terminal.