JP6524452B2 - Condenser type pickup cartridge - Google Patents

Description

  The present invention relates to a capacitor type pickup cartridge.

  Many of the pickup cartridges (hereinafter simply referred to as "cartridges") used for reproducing the sound recorded in the analog record are electromagnetic types using coils and magnets, and are speed proportional vibration-electric transducers It is. Since the cartridge of the electromagnetic type does not require a power supply but has a low output level, it is necessary to place a preamplifier having a high amplification factor at a later stage.

  Analog records record audio signals using RIAA recording characteristics. Therefore, when playing back audio from an analog record, it is necessary to restore the flat characteristics before being recorded. An equalizer is used to restore this characteristic. In order to return the RIAA characteristic to the original flat characteristic, it is necessary to make +20 dB correction at 20 Hz and -20 dB correction at 20 kHz in the equalizer. In the case where the above-mentioned correction is performed by adding an equalizer function to a pre-amplifier used in the subsequent stage of the electromagnetic cartridge, it is necessary to increase the voltage amplification factor of the pre-amplifier.

  Compared to the speed proportional type such as the electromagnetic type cartridge, the displacement proportional type such as the capacitor type cartridge has a high output level and a small amount of correction for restoring the sound signal to the flat characteristic. The above-mentioned preamplifier with a high amplification factor is unnecessary. However, since the capacitor type cartridge has a high impedance in the signal conversion unit, it is necessary to dispose an impedance converter using an FET. This impedance converter requires an operating power supply.

  In the capacitor type cartridge, an audio signal is taken out by a signal conversion unit including a cantilever including a stylus tip at its tip and a fixed electrode including an electret layer on a surface facing the cantilever. The capacitor type cartridge outputs an audio signal according to the sound groove formed on the surface of the analog record. When the stylus tip provided at the tip of the cantilever traces the sound groove, the cantilever vibrates accordingly. When the cantilever vibrates, the capacitance of the capacitor formed by the cantilever and the fixed electrode fluctuates according to the sound groove. This variation in capacitance is output as an electrical signal.

  Since the analog record is formed of a material such as resin, the surface on which the sound groove is incised is not flat but there is a slight distortion or the like. The cantilever fluctuates under the influence of distortion or the like of the analog record. Moreover, the variation of the cantilever due to the strain or the like is larger than that due to the sound groove. Therefore, the cartridge used for reproducing the analog record is provided with a space that can buffer the variation even if the cantilever is varied due to distortion or the like.

  In order to secure the above-mentioned space, the capacitor type cartridge is provided with an opening in a part of the cover which covers the signal conversion part. The cantilever protrudes from the opening to allow the stylus tip to trace the sound groove. Therefore, if the opening is too small, the cantilever may collide with the edge of the opening due to the above-mentioned vibration, and if the opening is too large, it may be a cause such as foreign matter mixed in the signal conversion part of the capacitor type cartridge. Become.

  Among known capacitor-type pickup cartridges, there is known one in which an oil having a damper property is interposed between a movable electrode (cantilever) and a fixed electrode to prevent foreign matter mixing (for example, see Patent Document 1). reference).

Japanese Patent Publication No. 52-15202

  By the way, in the capacitor type cartridge, the sensitivity becomes high according to the area in which the cantilever and the fixed electrode that make up the signal conversion unit face each other. In order to increase the area in which the cantilever and the fixed electrode face each other, the fixed electrode facing the cantilever may be extended to the vicinity of the stylus tip. However, since the signal conversion portion of the capacitor type cartridge has a very high electrical impedance and is easily capacitively coupled to an external noise source, the extension of the fixed electrode is susceptible to the influence of the external noise. In order to prevent the influence of external noise, an electrostatic shield may be provided around the signal conversion unit. In particular, an electrostatic shield may be provided to the opening provided for cantilever movement.

  The external noise sources that can be capacitively coupled to the signal conversion unit through the opening of the cantilever are, for example, an analog record and a turntable. The turntable does not become a noise source because it operates as an electrostatic shield if it is sufficiently grounded. However, when the turntable is not sufficiently grounded (e.g., when the turntable and the tone arm are not electrically connected), the motor drive system that drives the turntable and the power supply thereof can be a noise source.

  In addition, since nonuniform charge is partially accumulated due to peeling charge on the surface of the analog record, rotating the analog record may become a low frequency noise source.

  As described above, the capacitor type cartridge tends to cause electrostatic coupling with an external noise source when the signal conversion unit is enlarged to enhance sensitivity. Although an electrostatic shield is provided to prevent this, the effect of preventing external noise from being mixed with the electrostatic shield is reduced by increasing the space (opening) to prevent interference between the cantilever and the surrounding member due to fluctuations in the cantilever. I will.

  An object of the present invention is to provide a capacitor type pickup cartridge which can prevent the output of noise even if electrostatic coupling with a noise source occurs.

  The present invention is a capacitor type pick-up cartridge having a cantilever provided with a stylus tip at one end and a fixed electrode provided with an electret layer on the opposite surface to the cantilever, wherein an opening for allowing vibration of the cantilever is provided. An electrostatic shield provided, an induction electrode provided in the electrostatic shield, and a signal cancellation unit for canceling an electric signal induced in the induction electrode and an electric signal induced in the fixed electrode The main feature is having.

  According to the present invention, even if electrostatic coupling with a noise source occurs, the output of noise can be prevented.

FIG. 1 is a side view schematically showing an embodiment of a capacitor type pickup cartridge according to the present invention. It is a side view explaining the state of the electrostatic coupling with the external noise source in the above-mentioned capacitor type pickup cartridge. It is a side view which shows the structure of the said capacitor | condenser type | mold pick-up cartridge in detail. It is a side view explaining the state of the electrostatic coupling with the external noise source in the above-mentioned capacitor type pickup cartridge.

  Hereinafter, an embodiment of a capacitor type pickup cartridge according to the present invention will be described with reference to the drawings. First, the basic structure and the like of the cartridge 1 according to the present embodiment will be described with reference to FIGS. 1 and 2.

  The cartridge 1 is configured such that the signal conversion unit 30 protrudes obliquely downward from the opening 10 of the cover 100. The signal conversion unit 30 includes a cantilever 32 which is a pipe-like member, and a fixed electrode 34 facing the cantilever 32 to form a capacitor. The tip which is one end of the cantilever 32 is crushed so as to be flat. A stylus tip 33, which is a so-called record needle for tracing the sound groove formed in the analog record 50, is fixed to the tip. The other end of the cantilever 32, that is, the rear end is supported by an elastic support (not shown). In this manner, the cantilever 32 is supported in a cantilever manner, and the stylus tip 33 traces the sound groove of the analog record 50, whereby the cantilever 32 vibrates along the sound groove.

  The fixed electrode 34 is fixed along the length direction of the cantilever 32 and substantially parallel to the cantilever 32 at an appropriate distance from the cantilever 32. The fixed electrode 34 is an elongated plate-like member, and has an electret layer 35 on the surface facing the cantilever 32. The cantilever 32 and the fixed electrode 34 form a capacitor. The cartridge 1 can be used for reproduction of the stereo-recorded analog record 50, and the signal conversion unit 30 corresponding to the left channel and the right channel is provided independently. In FIG. 1, the signal conversion unit 30 only shows the cantilever 32, a set of fixed electrodes 34 and the electret layer 35, but the signal conversion unit 30 has another set of fixed electrodes 34 to correspond to the stereo output. An electret layer 35 is provided. That is, on a plane orthogonal to the length direction of the cantilever 32, two sets of the fixed electrode 34 and the electret layer 35 are attached at an angle of ± 45 degrees with respect to the vertical direction.

  As the stylus tip 33 traces the sound groove of the analog record 50, the cantilever 32 vibrates with horizontal and vertical vibration components. The vibration of the cantilever 32 changes the capacitance of the capacitor formed by the cantilever 32 and the fixed electrode 34. The cartridge 1 converts this change in capacitance into a change in voltage to generate an electric signal, and outputs signals of the left and right channels from the cantilever 32 and the two fixed electrodes 34.

  Since the output signal of the fixed electrode 34 has a very high impedance, it is converted to a low impedance by the impedance converter 36 and output from the cartridge 1. The impedance converter 36 is formed using a FET. The fixed electrode 34 is connected to the gate of the FET. The drain of the FET is connected to the output signal line 42. The source of the FET is connected to the signal line 44 together with the cantilever 32.

  Since the analog record 50 is formed of a resin disc, it is accompanied by a slight distortion or the like. The cantilever 32 vibrates as the stylus tip 33 traces the sound groove, but may be fluctuated more than the vibration due to the sound groove under the influence of distortion of the analog record 50 or the like. The opening 10 of the cover 100 is formed large as a space that allows the cantilever 32 to move so that the cantilever 32 can buffer a collision with the cover 100 even if the cantilever 32 is changed by the influence of strain or the like.

  As already described, since the electrical impedance of the fixed electrode 34 is high, it is necessary to provide the electrostatic shield portion 20 in the vicinity of the opening 10 and outside the cover 100 as shown in FIG. However, since the electrostatic shield portion 20 can not be provided in the opening 10, there is a possibility that the fixed electrode 34 and the analog record 50, and the fixed electrode 34 and the turntable 60 may be electrostatically coupled through this, respectively. .

  FIG. 2 equivalently illustrates a state in which the fixed electrode 34, the analog record 50, and the turntable 60 are electrostatically coupled. As shown in FIG. 2, when the electrostatic coupling is equivalently expressed, the first noise source 51 is connected between the fixed electrode 34 and the analog record 50 through the opening 10. Further, the second noise source 61 is connected between the fixed electrode 34 and the turntable 60 through the opening 10. In such a state, the output signal line 42 outputs noise that can be heard.

  The capacitor type pickup cartridge according to the present invention can prevent the output of noise even if the above-mentioned electrostatic coupling occurs. Hereinafter, the structure which exhibits the effect concerning this invention using FIG. 3 and FIG. 4 is demonstrated in detail.

  As shown in FIG. 3, an electrostatic shield 20 is disposed in the vicinity of the opening 10 of the cartridge 1 according to the present embodiment, and an induction electrode 11 is disposed outside the electrostatic shield 20. ing. The induction electrode 11 is fixed to the electrostatic shield portion 20 via the insulator 12.

  The cartridge 1 also includes a differential amplifier 40 between the fixed electrode 34 and the impedance converter 36. The differential amplifier 40 constitutes a signal cancellation unit that outputs the difference between the signals input from the two input terminals from the output terminal. The signal from the fixed electrode 34 corresponding to the output of the signal conversion unit 30 is input to one input terminal of the differential amplifier 40. The signal from the induction electrode 11 is input to the other input terminal of the differential amplifier 40. That is, from the differential amplifier 40, the difference between the signal from the fixed electrode 34 and the signal from the induction electrode 11 is output.

  As shown in FIG. 4, when the fixed electrode 34 and the analog record 50 are electrostatically coupled, the inductive electrode 11 and the analog record 50 are also electrostatically coupled. Then, the noise signal from the first noise source 51 is induced and output at each of the fixed electrode 34 and the induction electrode 11. Similarly, when the fixed electrode 34 and the turntable 60 are electrostatically coupled, the inductive electrode 11 and the turntable 60 are also electrostatically coupled. Then, the noise signal from the second noise source 61 is induced and output at each of the fixed electrode 34 and the induction electrode 11.

  The differential amplifier 40 outputs the difference between the two signals input as described above. The signal input from the fixed electrode 34 of the signal conversion unit 30 to the differential amplifier 40 is induced by the audio signal extracted from the analog record 50 and the noise signal induced by the first noise source 51 and the second noise source 61. It becomes a synthetic signal of noise signal. The signals input from the induction electrode 11 to the differential amplifier 40 are a noise signal induced by the first noise source 51 and a noise signal induced by the second noise source 61.

  Therefore, since the composite signal of the voice signal and the noise signal is input from one terminal to the differential amplifier 40 and only the noise signal is input from the other terminal, the noise signal is canceled out of the output signal. It becomes only an audio signal.

  The noise signal can be canceled more accurately by adjusting the level of the noise signal output from each of the induction electrode 11 and the fixed electrode 34 input to the differential amplifier 40 to be the same. Therefore, a level adjustment circuit may be disposed between the induction electrode 11 and the differential amplifier 40, and the level of the noise signal from the induction electrode 11 may be adjusted to match the level of the noise signal from the fixed electrode 34.

Reference Signs List 1 cartridge 10 opening 11 induction electrode 32 cantilever 33 stylus tip 34 fixed electrode 35 electret layer 40 differential amplifier

Claims (4)

A cantilever comprising a stylus tip at one end;
And a fixed electrode comprising an electret layer on the surface facing the cantilever.
An electrostatic shield provided at the opening for allowing the cantilever to vibrate;
An induction electrode provided on the electrostatic shield;
A signal cancellation unit for canceling the electric signal induced to the induction electrode and the electric signal induced to the fixed electrode;
A capacitor type pickup cartridge characterized by having: The induction electrode is fixed to the electrostatic shield via an insulating material.
A capacitor type pickup cartridge according to claim 1.   The capacitor type pickup cartridge according to claim 1, wherein the signal cancellation unit is a differential amplifier. A level adjustment circuit is disposed between the fixed electrode and one input end of the differential amplifier.
The capacitor type pickup cartridge according to claim 3.

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