Electrical resistors – Incased – embedded – or housed – Terminal or lead extends through casing or housing wall
Reexamination Certificate
2000-08-11
2001-11-13
Easthom, Karl D. (Department: 2832)
Electrical resistors
Incased, embedded, or housed
Terminal or lead extends through casing or housing wall
C338S233000, C338S236000, C338S243000, C338S271000, C338S273000, C338S307000
Reexamination Certificate
active
06317024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a resistor for audio equipment adapted for use in a high-fidelity amplifier in audio equipment.
2. Prior Art Description
In audio equipment, a high-fidelity amplifier is used to amplify the low level signals and reproduce sounds with good quality. Even slight variations in the electrical characteristics of the resistors used in high-fidelity amplifiers result in a major degradation of the sound quality. This has given rise to proposals to suppress variations in the characteristics of resistors caused by extraneous signal noise, to prevent the amplifier circuitry from being adversely affected.
JP-A 61-34901, for example, discloses an induction array of resistors for audio equipment applications in which, in order to improve the quality of reproduced sound, the induction field generated when electricity passes through the resistance film is utilized to minimize distortion with respect to the signal current.
In another example, JP-A 3-288401 relates to a shielded resistor comprising alternating layers of a magnetic film and a conductive film, in which extraneous noise is converted into heat energy, which is radiated away to prevent noise affecting the resistor in the shielding.
In another disclosure, JU-A 1-130501, the inside surface of the resistor carrier is formed in strips and the outside of the carrier is covered with shielding.
In all of the prior art resistors, the surface of the resistance film is sheathed to insulate the resistance film from the outside air. In one method, for example, the sheathing is coated on. The sheathing is usually a dielectric, so it is readily charged by external electrostatic induction. When this happens, there is a high possibility of the charge carriers causing variation in the electrical characteristics of the resistance film.
Moreover, when a magnetic sheathing is used, there is a high risk of the magnetism giving rise to phase distortion of signals applied to the resistor.
When the resistor carrier is cylindrical and comprises strips of resistance film on the inside surface and shielding on the outside surface, the shielding prevents the resistance film from being affected by the magnetism. However, with the shielding and resistance film being formed integrally with the resistor carrier, the signal flowing through the resistance film charges the resistor carrier, which can adversely affect signals applied to the resistor.
Also, a CLT-1 tester (made by Radiometer AS Copenhagen) or the like can be used to test the linearity of such resistors. At more than 120 db, the third high-frequency component included in a 10 KHz signal is known to be low. However, an examination into the factors causing variations in the characteristics of such resistors revealed the following. The present inventor used a Hewlett-Packard 4284A LCR Meter to measure the inductance produced when resistance films are subject to spiral cutting, and the capacitance resulting from using sheathing to directly protect the resistance films. At high audio frequencies, no inductance component was detected, just a change in the capacitance component of 40 db or more.
These results reveal that the sound sensitivity is affected not by the inductance component of the resistor, but only by the capacitance component, which depends on the dielectric sheathing. That is, the sheathing is in direct contact with the resistance film and therefore is charged by electrostatic induction, thereby affecting signals applied to the resistance film.
Based on these findings, the object of the present invention is to provide a resistor for audio equipment that is able to prevent audio replay containing unusual sound quality caused by the effect on the characteristics of a resistance film caused by the resistor sheath becoming charged by electrostatic induction.
SUMMARY OF THE INVENTION
To attain the above object, the present invention provides a resistor for audio equipment, comprising: a resistor body; a first electrode attached to a first end of the resistor body; a second electrode attached to a second end of the resistor body; the resistor including a substrate, a resistance film formed to cover the substrate surface, and a groove of constant width formed in the resistance film, exposing the substrate surface; a sheath formed to encompass the resistance film formed with a space around the outer surface of the resistor body; and a conductive film formed on an internal surface of the sheath; the conductive film having an annular insulating slit formed at a predetermined position along an axial line of the resistor body that exposes the sheath surface, whereby the resistor body is axially separated into a first conductive film portion and a second conductive film portion.
The conductive film does not have to be formed only on the inside surface of the sheath, but may be formed so as to also cover the outside surface of the sheath.
Also, it is preferable for the insulating slit to be formed at a central point along the axis of the resistor body.
With this configuration, the fact that the resistance film is formed on the resistor surface facing the conductive film on the sheath side, with a space therebetween, makes it more difficult for the resistance film to be subjected to the effects of extraneous electrostatic induction.
The part of the resistance film facing the insulation slit formed at a point in the conductive film midway along the resistor body will probably become charged slightly. However, the charge produced in the insulation slit by the electrostatic induction and the charge produced by signals applied to the conductive film will cancel each other out. Therefore, the electrostatically induced charge on the sheath prevents signals applied to the resistance film from having an effect.
Incorporating the resistor of the invention in an amplifier will prevent the signals from being affected by extraneous noise, thereby ensuring the fidelity of the reproduced sound.
The resistor of this invention can also include first and second cap electrodes set into the ends of the sheath. In this case, a configuration can be used in which the first electrode is inserted between the first cap electrode and the first end of the resistor, and the second electrode is inserted between the second cap electrode and the second end of the resistor. Also, it is preferable in this case for the space between the resistance film and the conductive film on the sheath to be sealed by the cap electrodes. The space can be filled with air or inert gas.
Alternatively, the sealed state can be used to maintain a state of reduced pressure in the space.
Filling the space between the resistance film on the resistor body and the conductive film formed on the sheath with air or inert gas is an effective way of suppressing the adverse effect on the resistance film of the electrostatic induction of the sheath. This can also be done by using a reduced-pressure gap.
It is preferable to use a sealant to ensure the cap electrodes inserted into the ends of the sheath form a hermetic seal.
The resistor of the invention can also include a first lead wire that passes through the first cap electrode to the first electrode, and a second lead wire that passes through the second cap electrode to the second electrode. In this case, it is preferable for sealant to be used where the lead wires pass through the cap electrodes to provide a hermetic seal.
Further features of the invention, its nature and various advantages will become more apparent from the accompanying drawings and following detailed description of the invention.
REFERENCES:
patent: 2898570 (1959-08-01), Patrichi
patent: 3136972 (1964-06-01), Randolph
patent: 3136973 (1964-06-01), Randolph
patent: 3173121 (1965-03-01), Murry
patent: 3173122 (1965-03-01), Murry
patent: 3199058 (1965-08-01), Cramor
patent: 3803528 (1974-04-01), Wellard
patent: 4016527 (1977-04-01), Francis et al.
patent: 4678890 (1987-07-01), Sorrow
patent: 61-34901 (1986-02-01), None
patent: 1-130501 (1989-09-01), None
patent: 3-288401 (1
Burns Doane Swecker & Mathis L.L.P.
Easthom Karl D.
Takman Electronics Co., Ltd.
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