JPS5822830B2 - Tone arm return position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a return position detection device for a tone arm of a record player.

A record player performs playback by moving a pickup along the sound groove of a record placed on a rotating turntable.
Most of them use a method that automatically returns the tone arm.

As a method for automatically returning the tone arm, there is a method of detecting that the pickup has reached a predetermined distance from the center of the turntable and activating the return device.

However, with this method, the position of the lead-out groove may differ slightly depending on the record, so if a record that is located relatively outside is used, automatic return is not possible, and a record that is located inside and has a relatively long playing time is used. The drawback is that the tone arm automatically returns to its original position before the performance ends.

Another method is to utilize the fact that the feed pitch of the lead-out groove of the record groove is smaller than the feed pitch of the sound groove, and this method will be explained with reference to the drawings.

Figure 1 is an ideal graph showing the amount of displacement with respect to the travel time of the pickup, and A and B show the amount of displacement Q(t) when the pickup traces the sound groove and the lead-out groove. Let Ql be the average increase rate of Q(t), and let Q2 be the average increase rate in the lead-out groove.

Furthermore, let Qo be the standard increase rate, and Q 1 <
It is determined that Qo < Q2.

This method detects that the amount of displacement when the pickup enters the lead-out groove increases significantly compared to the amount of displacement when the pickup traces the sound groove, as shown in Figure 1, that is, Q(t)〉Qo. The tone arm automatic return device is activated.

However, the diameter of the center hole of the record almost never completely matches the diameter of the rotating shaft of the turntable, and as a result, positional deviation occurs as the turntable rotates.

Eccentricity accompanying this positional deviation causes wobbling in which one rotation is one period.

For this reason, the amount of displacement corresponding to the travel time of the pickup is actually 1/1 of the turntable as shown by curve C in Figure 1.
It fluctuates with each rotation as one cycle.

Now, the value of increased dust Q(t) at a point in the positive direction of this curve C is assumed to be Q3.

The increased amount of dust Q3 that changes depending on the degree of positional deviation of the center hole of the record is the standard increased amount of dust Q.

In some cases, it becomes more like a dog.

In such a case, as before, Q(t)(-Qa)
>Qo is detected and the tone arm is returned erroneously.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly reliable tone arm return position detection device that prevents malfunctions due to eccentricity due to differences in the position of the lead-out grooves and misalignment of the center hole of the record.

Hereinafter, the present invention will be explained using the drawings.

FIG. 2 is an example of a circuit according to the present invention.

Between the sensor consisting of a light emitting element such as a lamp 1 and a light receiving element such as Cd52 which are connected in series with a resistor R1 to the positive and negative bus lines, there is a shutter 3 which rotates in conjunction with the rotation axis of the tone arm and blocks light. It has been inserted.

The shutter 3 operates from closed to open in response to the pickup moving from the sound groove to the center of the record.

The structure is such that the amount of light received by Cd52 increases accordingly.

One side of Cd52 is connected to the positive bus line, and the other side is connected to the transistor T1.
are connected to their respective emitters.

The collector of the transistor T1 is connected to the negative bus through a resistor R2, and the base is connected to a voltage dividing point of a voltage dividing circuit made up of resistors R3 and R4.

The output voltage of the transistor T1 changes in response to an increase or decrease in the amount of light received by Cd52.

For example, when using a record with a difference in the diameter of the center hole of the record and the diameter of the rotation axis of the turntable, or when the center hole of the record is eccentric, the output voltage of the transistor T due to the eccentricity due to positional deviation. is as shown in Figure 1C.

Then, as the tone arm moves toward the inner circumference of the recorder, the shutter 3 gradually moves from closed to open, as shown in FIG.

If the output of the transistor T1 is compared with a reference voltage, the output will be different between the inner and outer circumferences of the record, and direct comparison cannot be made as it is.

Therefore, the first
The waveform in Figure C becomes like the waveform in Figure 3.

According to the waveform in FIG. 3, while the output of the transistor T was gradually increasing, the differential output remained constant and a predetermined voltage d was obtained only when the tone arm was positioned in the lead-out groove. All you have to do is compare the voltage d with the reference voltage.In the differential output, if the output due to eccentricity is large, the difference between the output e during performance and the output d of the derived groove will be small, and the so-called S/N will deteriorate. Therefore, if the eccentricity is large, it will malfunction.

Therefore, by providing an integrating circuit consisting of a resistor 6 and a capacitor C2 at the rear end of the differential output, that is, C1, the S/N ratio can be improved.

Figure 4 shows the waveform when it passes through the integrating circuit, and the output e during performance among the differential outputs is averaged by passing through the integrating circuit, further improving the S/N between points d and f. Become.

Therefore, from this output, the position of the lead-out groove of the record, that is, the return position of the tone arm, can be easily and reliably discriminated, and malfunctions can be prevented.

Note that the return position is detected by supplying the signal to a comparison circuit via the output terminal 5 and comparing it with a predetermined reference level.

The output of the comparison circuit is used to operate an automatic reset device.

As explained above, according to the present invention, by using a simple electronic circuit, the position of the lead-out groove of the record does not matter, and the influence of eccentricity due to positional deviation of the center hole of the record is eliminated.

Furthermore, in the present invention, a photoelectric detector is used for detecting a signal corresponding to the displacement of the pink-up, but other means for obtaining a signal corresponding to the position of the pickup, such as magnetic change or capacitance change, may also be used. Regardless of the method used, the same effects as those described above can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the amount of displacement with respect to the travel time of the pickup, Fig. 2 is an example of a circuit according to the present invention, and Fig. 3 is a graph showing the amount of displacement with respect to the travel time of the pickup.
FIG. 4 is a waveform diagram when the waveform shown in the figure is passed through a differentiating circuit, and FIG. 4 is a waveform diagram when the waveform shown in FIG. 3 is further passed through an integrating circuit. Explanation of symbols of main parts, 1...Lamp, 2...
...CdS, 3...Shutter, 4...
...Differential circuit and integral circuit.

Claims (1)

[Claims] 1 Consists of a light emitting element, a light receiving element and a shutter,
The device comprises a detection means for obtaining a signal according to the position of the pickup, a differentiating circuit receiving the signal of the detecting means as an input, and an integrating circuit receiving the signal of the differentiating circuit as an input, and the differentiating circuit and the integrating circuit are connected in series. A tone arm return position detecting device for a record player, characterized in that by connecting the tone arm, frequency components due to eccentricity are reduced and the return position of the tone arm can be reliably determined.