US 2924776 A
Description (OCR text may contain errors)
Feb. 9, 1960 R. H. PETERSON TUNER Filed July 26, 1955 DIV.
lso- LAToR OCTAVE [03 SELECTOR OSCILLATO R d NoTE SELECTOR INVENTOR RICHARD H. Pn'EnsoN T0 NOTE SELECTOR United States Patent O TUNER Richard H. Peterson, Chicago, Ill. Application July 26, 19,55, Serial No.A 524,500
4 Claims. (Cl. 324-79) My invention relates to tuning musical instruments, and to electronic equipment for doing so. More specically, it relates to an electronic tuning standard of great stability, and to convenient electronic means for comparing the frequencies of the standard and of the instrument being tuned.
In the accompanying drawings:
Figure l is a general wiring diagram, with certain of the parts identified by block showing for convenience and simplicity;
Figure 2 is a wiring diagram of a frequency changer; and
Figure 3 is a wiring diagram of the oscillator and its isolation amplifier.
The musical scale, known as the equal tempered chromatic scale, is known to be a compromise, because the ratios of the musical pitches are not exactly in the ratios of small integers. Thus, based on A3 435, C3 is 258.65, but G3 is not 387.98. Instead, it is 387.54, and such fractional discrepancies in frequency permeate the entire series of compromises that make it possible for a single instrument to play in different keys.
The adjustment of these discrepancies, in a musical instrument, makes a difference in performance that is very marked to the trained ear of a person of aesthetic sensibilities; and many great musical artists are extremely exacting in requiring pianos, harps, etc., to have a certain temperament, even to the extent of taking with them their own piano, or their own personal piano tuner, or both.
According to the invention it is possible to provide a reference standard of such accuracy and precision that the standard itself can be made up to give a particular desired temperament. The complete adjusted standard, then, enables a person of mediocre, or even non-existent, discrimination by ear with respect to pitchto produce and reproduce repeatedly the temperament determined by the reference standard.
In the embodiment selected to illustrate the invention, the oscillator l is of exceptional characteristics, in the sense that the frequency it generates is completely independent of variations in power-line voltage and powerline frequency. It is also independent of the condition or age of the tubes. It is provided with tuning means to cause it to generate at least one complete octave of notes, with the temperament constant and dependable.
The signal from the oscillator may be compared with the corresponding note of the instrument to be tuned by ear, or. the signal from the standard and from the instrument to be tuned can be combined, electronically or otherwise, to generate a beat parison will give one complete octave with the exact temperament desired.
Having retained one complete octave of perfect ,tem-
yperament, it is quite possible to go down or up the scale by ear and tune all the other octaves, but that requires a sensitive and trained ear, and is a relatively exacting task. According to the invention, a series of frequency This simple comchangers is used so that the operator can switch over from the oscillator signal itself to the output of a rst frequency divider or multiplier and tune the adjacent octave, and so on down or up as far as desired. In the embodiment illustrated, only six octaves are provided.
The basic temperament vThe oscillator 10 conveniently includes a tapped inductance 12 for the purpose of tuning it with precision to each of the notes of a complete octave. The working inductance comprises vtwo portions in every instance. There is the pre-selected fraction of the main inductance 12, and a series of relatively much smaller trimmer coils 14, 16, 18, 20, 22, 24,26, 28, 30, 32, 34, 36 and 38, associated in series relationship with the taps on the main inductance.
In each instance, the magnitude of the operating portion of the main inductance 12 is many times greater than that of the trimmer coil. The main inductance has little or no ferro-magnetic action; in the best designs, none at all. Therefore, its inductance is substantially independent of circuit constants and voltages. A minor fraction, usually amounting to less than one percent, of the total inductance is contributed by the trimmer coil, which can be adjusted by a simple ferro-magnetic core 40 over a narrow range. It will be obvious that if the actual magnitude of the trimmer coil inductance is one percent of the total, a variation of one percent in the trimmer coil will only represent a variation of one one-hundredth of one percent in the total inductance. In vthis way a very quick and precise adjustment for temperament can be provided, which will remain for long periods of time so unaffected by any operating condition that the most sensitive ear does not detect the variation.
The frequency delivered by the oscillator is a function of both the inductance and the capacitance of the tuned circuit. I have illustrated a primary capacitor 42 especially constructed to remain of constant capacity over long periods of time and wide variations of temperature. To provide capacitors of such quality throughout the apparatus as a whole would be prohibitively expensive, but the cooperating relationship between this capacitor and the others is such that the others can be relatively cheap and ordinary capacitors of a much lower degree of constancy without atfecting the eifective constancy of the tuner as a whole.
Thus, in parallel with capacitor 42 there is provided a series of additive capacitors, of which ten are illustrated. Any selected one of the trimming capacitors 44, 46, 48, 50, 52, 54, 56, 58, 60 and 62, may be connected by the selector switch 64, in parallel with capacitor 42; land these capacitors are of progressively increasing size, such that the first one will lower the frequency about 0.05 of a semi-tone, and the next will lower it 0.1 of a semi-tone, and so on. This degree of precision is essential to make it possible to tune one piano or pipe organ etc., unto perfect unison with another instrument which has already been tuned. It will be apparent that all the trimming capacitors may be ordinary relatively cheap condensers not particularly immune to slight variations due to temperature or humidity. These trimming capacitors adjust the basic pitch of the entire reference standard without any change in its temperament.
Referring now to Figure 3, the oscillator 10 illustrated is a form of a Hartley oscillator, but the grid capacitor 66 is exceptionally small, for instance, three percent of the capacitance of the main tuning capacitor 42. I have found that careful adjustment of this ratio can be made to produce an oscillator of highly constant frequency, regardless of tube age, or the voltage supplied, or any other operating condition.
From the oscillator 10, the signal goes iirst to the isolator 68. This is an ordinary triode amplifier, except that it is operated as a limiter, and distorts the sine wave signal of the oscillator to a complex wave form. In addition, its output voltage remains relatively constant even though the amplitude of the oscillation received may vary somewhat, depending on which semi-tone the oscillator 10 is delivering.
In a typical instance, this frequency band may cover the semi-tones within a range from about 2048 cycles per second to about 4096 cycles. The precise values may be Varied by the user, depending on the previous adjustment of the trimming capacitors.
The signal from the isolator 68 is delivered toy the grid of a second tube at 70 forming part of `the first frequency changer 72. This frequency changer is a divider, and one of several types well known in the art,
and commonly referred to as anEccles-Jordan circuit. The triodes 74 and 76 are interconnected in such a way that when either one is conducting, it will bias the other one and prevent the other one from conducting, but the trigger impulse from the tube 70 will upset this bias and let the tube that was previously not conducting begin to conduct and prevent its companion tube from continuing to conduct. Thus, each of the tubes 74 and 76 functions in an on-and-oif or ip-ilop fashion, and the tubes change places each time an impulse is received from the tube 70, so that the cycle of each of `these tubes requires two cycles of the tube 70 to arrive at completion.
From the divider 72 a conductor delivers signal to terminal of the octave selector 78, and with the selector turned to that terminal, the user may now tune the octave between the frequencies of 1024 and 2048 by moving the note selector consecutively from one note to the next.
Fromthe divider 72 a; conductor `80 delivers'signal to the tube 70 of the second frequency divider 82. Therefore, the main tubes of the second frequency divider will complete their cycle during two cycles of the first frequency divider. From the second Vfrequency divider a conductor 84 delivers the signal from that divider to terminal 4 of the octave selector. I
- It will be apparent that any number offrequency dividers can be connected in a cascade in this way, and that each frequency divider can have'its resistors and capacitors proportioned to function efficiently for the frequencies which it receives and delivers. I have illustrated only live dividers, in which the divider 82 takes care of the octave from 512 to 1024; the divider 86 covers from 256 to 512; the divider 88 covers from 128 to 256; and the divider 90` from 64 to 128.
Beat com parison The signal from the octave selector may be delivered to a loud speaker through the capacitor 92, protective resistor 94 and potentiometer resistor 96, Vfor Volume control by the user. The signal is amplified conventionally by tubes 98 and 100, and delivered to the primary winding 102 of a conventional loud speaker 103.
A person with a fairly well-trained ear can do an excellent job by merely listening to the instrument and to the reference loud speaker 103. However, to speed up the work of such a person, and to enable persons whose own musical discrimination'is insufficient to do equally good work, means are provided for producing a beat note. The terminals 104 may be yconnected to a microphone receiving the tone of the instrument' being tuned. In the case of an electronic instrument, the terminals 104 may be connected directly to the appropriate terminals of the electronic instrument. The signal coming into the terminals 104 is transferred by a conventional transformer 106 and delivered at the point 108 where it blends with the signal coming in from the octave selector and produces a beat in the transformer 110.
The 15 ohm, 10 watt resistor 112 is a dummy load to replace the normal load on the electronic musical instrument. It yassures normal functioning of the instrument being tuned during the tuningvoperation.
The sharpness ofthe beat in the loud speaker 103 is materially enhanced if distortion is introduced into the amplifier circuit. I have illustrated a distorting circuit comprising conductor 114, rectifier 116 and conductor 118. 'I'he distorting circuit is rendered operative by contacts 120 carried by the same conventional jack as terminals 104.
It will be noted that selection and installation of all trimmer capacitors is completed at the factory, and this part of the equipment is never touched or disturbed by the user. which are carefully adjusted at the factory as one of the final stages of manufacture of the unit and are never adjusted by the user.
Others may readily adapt the invention for use under various conditions of service by employing oner or more of the novelr features disclosed, or equivalents thereof.
For instance, the oscillator could operate one or more octaves lower or higher, with a corresponding change in the number of frequency dividers, or with no frequency dividers at all. It could also be provided with frequency multipliers to deliver any desired number of octaves above that are generated by the oscillator itself. A relatively small adjustable capacitor 122 connected in parallel with capacitor 66 will change the ratio or spread of the frequencies of the different semi-tones to get extra precision in frequency.
With respect to the apparent scope of my invention, I desirey to claim the following subject matter:
1. In a high precision tuner, of the type comprising a precision reference standard oscillator and means for comparing oscillations from said standard with oscillations from the instrument being tuned; a reference oscillator comprising a triode and a tank circuit; said tank circuit comprising an inductor and a capacitor; said triode having a cathode and a grid and a plate; said inductor having a `series of semi-tone taps corresponding to the twelve notes of the chromatic scale; a grid-cathode circuit including a selector switch, a connection from said grid to said selector switch; said selector switch engaging a selected one of said semi-tone taps; said inductor having a cathode tap connected to said cathode; a D.C. blocking capacitor inserted in said grid cathode circuit between said selector switch and said grid; said blocking capacitor being of very small capacitance compared to said tank circuit capacitor, and of the order of magnitude of three per cent of said tank circuit capacitance.
2. A combination according to claim l in which said tank circuit inductor has said semi-tone taps positioned to secure the pitches of the notes of the musical chromatic scale with approximate accuracy; there being a small adjustable trimming inductor in series with each of said taps for precision adjustment of each semi-tone; said tank circuit capacitance including said first-mentioned capacitor, and a plurality of smaller trimming capacitors, arranged to be connected selectively in parallel with said main capacitor to adjust the overall frequency of all the semitones without affecting the relative frequency ratios, or temperament, determined by said main and tap inductors.
3. A combination according to claim 2, in which said trimmer inductors are provided with ferromagnetic cores; said main inductor being devoid of magnetic material.
4. A combination according to claim 2, in which said inductor taps include only twelve adjacent semitones; there being a cascade of 2-to-l frequency dividers controlled by said reference standard; and additional connections for comparing the oscillations of the instrument being tuned with the output signal from any selected one of said dividers.
(References ou following Page) The same applies to all the trimmer coils, l
5 References Cited in the le of this patent 2,730,681
UNITED STATES PATENTS 1,846,314 Crossley Feb. 23, 1932 1,947,187 Clark Feb. 13, 1934 5 1,982,340 Forbes Nov. 27, 1934 2,087,652 Oakley July 20, 1937 2,543,629 Hanert Feb. 27, 1951 2,680,198 Bick June 1, 1954 pgs. 448-464.
6 Went Ian. 10, 1956 Krauss Sept. 17, 1957 Tennes Sept. 17, 1957 OTHER REFERENCES The Temperature Coecent of Inductance, article, Proceedings of the I.R.E., April 1937, vol. 25, No. 4,