JPS6234086B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stylus pressure display device for a record stylus, and in particular is configured to display the stylus pressure when the stylus pressure exceeds a predetermined value.
This is to eliminate incorrect display of stylus pressure. A detailed description will be given below with reference to embodiments shown in the drawings. First, the stylus force measuring means for the record stylus will be explained. In this embodiment, the Hall voltage output from the Hall element 1 is changed by changing the magnetic field applied to the Hall element 1 in accordance with the stylus pressure,
Therefore, this Hall voltage is used as an amount indicating the stylus pressure. As shown in FIG. 4, a pair of magnets 3 are attached to the open end side of the leaf spring 2, one end of which is fixed, and a Hall element 1 is placed in the magnetic field formed by the magnets. The magnetic field applied to the Hall element 1 is changed by directly or indirectly placing the record stylus 5 attached to the record stylus 5 on the open end of the leaf spring 2 and changing the position of the magnet 3 in accordance with the stylus pressure. , hence Hall element 1
The Hall voltage output from the stylus is used as an amount indicating the stylus force. By the way, since the stylus pressure-voltage conversion system using a magnet and Hall element has a negative temperature coefficient (approximately -0.2%/°C for the entire system), in this embodiment, Hall element 1 is driven. A positive temperature characteristic is given to the current source 6 for this purpose. Since the conversion gain of the Hall element 1 is proportional to the drive current, temperature compensation of the stylus pressure-voltage conversion system becomes possible by changing the drive current in response to temperature. That is, in the current source 6 (constant current circuit) composed of resistors R ₁ , R ₂ , R ₃ and transistor Tr ₁ shown in FIG. 2, the current value (I) is (However, V _BE is the voltage between the base and emitter of the transistor.) However, since V _BE has a temperature coefficient of -6 mV/℃, the temperature coefficient of the constant current circuit can be adjusted by appropriately selecting the voltage drop due to resistor _R1 . Approximately +0.2%/
℃, it is possible to eventually compensate for the temperature of the stylus pressure-voltage conversion system. A Hall voltage having a value corresponding to the stylus pressure is amplified by a differential amplifier circuit 10 having a high input impedance. The differential amplifier circuit 10 includes two differential amplifiers 1.
1 and 12 and semi-fixed resistors 13 and 14, and variations in the offset voltage and conversion gain of the Hall element are adjusted by the semi-fixed resistors 13 and 14, respectively. That is, the output voltage of the differential amplifier 12 is ideally adjusted to zero when the stylus force is not being measured. The output of the differential amplifier circuit 10 is input to the zero point correction circuit 20 . Here, after correcting variations in the characteristics of the differential amplifier and Hall element, fluctuations in offset voltage due to mechanical positional deviation of the stylus pressure measuring means (misalignment of the positional relationship between the magnet and Hall element) and temperature changes are considered. be compensated. That is, since the output voltage of the differential amplifier 12 that occurs due to positional deviation or temperature change does not indicate the stylus pressure, it is The zero point correction circuit 20 is a circuit for suppressing this output voltage to a low level. Zero point correction circuit 2
0 mainly consists of two operational amplifiers 21 and 22, and relay 2.
3. It consists of a capacitor _C1 , a transistor _Tr2, etc., and is linked to the tone arm. (This switch is turned on when the tone arm is on the armrest, and turned off when it is removed from the armrest.) ) is in the zero point correction state when it is in the on state, and when it is in the off state, it amplifies and outputs the voltage corresponding to the stylus pressure. More specifically, when switch S is on, that is, when the tone arm is on the armrest, the potential at point C is low (the value of resistor _R10 is small compared to the value of resistor _R8 , and capacitor _C2 is The transistor Tr ₂ (which is almost in a discharge state) is in an off state, and the relay 23 is also in an off state, so that the relay contact is in contact with the NC side. At this time, the operational amplifiers 21 and 22 constitute a closed loop, and the output voltage V _B (voltage at point B) of the operational amplifier 21 is the input voltage V _A on the non-inverting input side of the operational amplifier 21. A value compressed by a closed loop gain of 22, i.e. Therefore, the capacitor _C1 is charged with this output voltage _VB . Therefore, operational amplifiers 21,2
By selecting a sufficiently large closed loop gain of 2, the voltage V _B , which is preferably 0, can be suppressed within the error range of the stylus pressure measurement system in the non-stylus pressure measurement state. Now, with the tone arm removed from the armrest stand and the record stylus placed in the predetermined position of the stylus force measuring means, switch S
is in the off state, and the power supply (+V) is applied to the base of transistor Tr ₂ via resistor R ₈ , so
This transistor Tr ₂ is turned on, and therefore the relay 23 is also turned on, so that the relay contact is switched to the NO side. In this state, the voltage of capacitor _C1 is maintained as it is, and operational amplifier 2
On the output side of 1, the change in the voltage at the non-inverting input point A of the operational amplifier 21 based on the measurement of the stylus pressure of the record stylus, that is, the voltage corresponding to the stylus pressure is expressed as the gain of the operational amplifier 21 (R ₄ /R ₅ +1 ) is amplified and output. Therefore, the zero point correction circuit 20 outputs a voltage corresponding to the stylus pressure after removing the effects of the above-mentioned positional deviation and temperature change, that is, automatically correcting the zero point. Note that the transistor Tr ₂ turns on after a time delay corresponding to the time constant determined by the resistor R ₈ and the capacitor C ₂ after the switch S turns off, but this time constant is set small and the tone arm The transistor Tr ₂ is always turned on before the record stylus is removed from the armrest stand and the record stylus is placed at a predetermined position on the stylus pressure measuring means.
The reason why the time constant circuit 24 consisting of resistor R ₈ and capacitor C ₂ is provided is that even if the tone arm is removed from the arm rest, power is turned on to the record player, and then the tone arm is returned to the arm rest. Even if the record stylus is placed at a predetermined position on _the stylus pressure measuring means, the zero point correction is always performed before _such stylus pressure measurement. The transistor Tr ₂ is turned off and zero point correction is performed during this period. That is, the time constant circuit 24 serves as an erroneous measurement prevention circuit to prevent stylus pressure measurement from being performed without zero point correction in the above-mentioned case. By the way, the voltage of capacitor _C1 (zero point correction voltage) is determined by the capacitance of capacitor _C1 and the operational amplifier 22.
Although the voltage changes with time due to a time constant determined by the impedance of the non-inverting side input, this voltage change causes a measurement error in the stylus force. Therefore, it is necessary to measure the stylus pressure within a certain period of time after removing the tone arm from the armrest stand to prevent voltage changes from becoming too large. Therefore, a time constant circuit 25 consisting of a resistor _R9 and a capacitor _C3 is provided, and based on the output of this circuit 25, a blanking signal for displaying the stylus pressure is obtained. That is, since the resistance value of resistor _R10 is smaller than that of resistor _R9 , when the tone arm is on the armrest stand and switch S is in the on state, capacitor _C3 is almost in a discharged state. The potential at point D is low, and the potential at point D is low after a predetermined period of time (for example, 2 minutes) has elapsed since the switch S was turned off and charging of the capacitor _C3 was started, that is, after the stylus pressure measurement state was entered. becomes a high level, and this becomes a blanking signal for stylus pressure display. Therefore, when such a predetermined period of time has elapsed, it is necessary to once return the tone arm onto the armrest table, adjust the zero point again, and then measure the stylus pressure. From the above explanation, it can be seen that the time constant circuit 25 serves as a circuit for preventing erroneous measurements. Note that the influence of the voltage change of the capacitor C ₃ on the error in stylus pressure measurement increases as the closed loop gain of the operational amplifier 22 increases, so from this point of view, it is desirable to keep the closed cape gain small. Now, the output voltage of the zero point correction circuit 20 in the stylus pressure measurement state is input to the AD conversion circuit 30 , and a digital signal corresponding to the stylus pressure is output from the output side of this circuit. The A-D conversion circuit 30 includes a clock generation circuit 31 and BCD counters 32a and 32.
b, a 4-bit DA converter, 33a, 33b, a comparator 34, and an adder 35. The clock generating circuit 31 is an unstable multivibrator composed of inverting amplifiers 31a, 31b and capacitor resistors, and the generated clock is up-counted by two-digit BCD counters 32a, 32b. The count outputs of the BCD counters 32a and 32b are output from the DA converters 33a and 33, which are composed of ladder resistors whose resistance values have a relationship of R-2R.
The signal is converted into an analog signal at step b, and further weighted and added at an adder 35 composed of resistors 35a and 35b having a resistance value of 1:10. The output voltage of the adder 35 and the output voltage of the zero point correction circuit 20 are input to the comparator 34, and at the point when the output voltage of the adder 35 exceeds the output voltage of the zero point correction circuit 20 , the output voltage of the comparator 34 is inputted to the comparator 34. is inverted to low level.
This inversion to low level becomes a latch signal. That is, at this point, the BCD counters 32a, 3
The count output of 2b indicates the stylus pressure from the zero point correction circuit 2.
Since the output voltage of 0 is converted into a digital value, if the count output at this time is latched and displayed, the stylus force will be digitally displayed. The count outputs of the BCD counters 32a, 32b are input to display control circuits 40a, 40b. The display control circuits 40a and 40b have a latch function, BCD
It has a decoder function that converts the output to a 7-segment display output, and a driver function that drives the 7-segment light emitting diode. Display control circuit 40
The outputs of a and 40b are applied to indicators 41a and 41b via current limiting resistors, so that the stylus pressure is digitally displayed in two digits. However, in the present invention, the stylus pressure is configured to be displayed only when it reaches a predetermined minimum value (0.5 g in this embodiment). That is, if the stylus pressure is too small, it cannot be accurately measured by the stylus pressure measuring means, and if this is to be displayed, it will be displayed incorrectly. In particular, when the displays 41a and 41b are configured to display other information (for example, the number of revolutions of the record, etc.), other information is normally displayed.
It is desirable to switch to the stylus pressure display state when the stylus pressure reaches 0.5 g or more and accurate display becomes possible.
Therefore, in this embodiment, the stylus pressure is displayed when the stylus pressure is 0.5 g or more and within 2 minutes after the tone arm is removed from the armrest base. A display instruction circuit 42 that enables display of the stylus pressure when the stylus pressure exceeds a predetermined value is comprised of a comparator. An analog voltage corresponding to the minimum display stylus pressure of 0.5 g is input to the non-inverting input side of the comparator 42, and the output voltage of the zero point correction circuit 20 is input to the inverting input side, so that the stylus force is When the voltage exceeds 0.5g, the output of the comparator 42 is inverted to low level. This inverted output to low level becomes the display instruction output. In this embodiment, the stylus pressure can be displayed within two minutes after the tone arm is removed from the armrest base, so the display instruction output is sent to the gate 43 together with the output of the time constant circuit 25. It has been entered. The output of gate 43 is normally at a high level, and the output of BCD counter 3
2a and 32b are set to a clear state, and display control circuits 40a and 40b are set to a blanking state. While the output of the comparator 42 is inverted to low level and the output of the time constant circuit 25 is low level, the output of the gate 43 is low level, and in response to this inversion to the low level state, the clear state is established. It is released and the BCD counters 32a, 3
2b starts, and when the DA conversion value of the count output matches the analog voltage indicating the stylus pressure, the count output at this point is latched and digitally displayed as the stylus pressure. As described above, the device of the present invention includes a stylus pressure measuring means for measuring the stylus pressure of a record stylus and outputting an electrical signal corresponding to the stylus pressure, and a counter based on the electrical signal output from the stylus pressure measuring means. a display device that digitally displays the count output from the tone arm, a gate that outputs a blanking signal to the display device after a certain period of time after the tone arm is removed from the armrest base, and a needle measured by the stylus force measuring means. The present invention provides a stylus pressure display device for a record stylus, which includes a display instruction circuit that enables the display device to display an indication when the pressure exceeds a predetermined minimum value.
When the stylus pressure reaches a predetermined minimum value, it can digitally display the stylus pressure for a certain period of time, which prevents erroneous indications of small stylus pressure that cannot be accurately measured. . In particular, if the display device is configured to display other information as well, it is advantageous because other information can be displayed when the stylus force is below a predetermined minimum value, which cannot be displayed accurately.

[Brief explanation of the drawing]

The drawings all show the stylus pressure display device for a record stylus according to the present invention; FIG. 1 is an overall block diagram, FIGS. 2 and 3 are detailed views of a portion of FIG. 1, and FIG. FIG. 2 is a diagram showing a stylus pressure measuring means. 1 and 3 are Hall elements and magnets constituting the stylus pressure measuring means; 20 is a zero point correction circuit; 30 is an AD conversion circuit; 41a and 41b are indicators; and 42 is a comparator (display instruction circuit).

Claims (1)

[Claims] 1. A stylus pressure measuring means that measures the stylus pressure of the record stylus and outputs an electrical signal corresponding to this stylus pressure, and digitally displays the count output from the counter based on the electrical signal output from the stylus pressure measuring means. a display device, a gate that outputs a blanking signal to the display device after a certain period of time after the tone arm is removed from the armrest base, and a stylus pressure measured by the stylus pressure measuring means that exceeds a predetermined minimum value. A stylus pressure display device for a record stylus, comprising a display instruction circuit that enables the display device to display when the stylus pressure is stylus.