JPS5830269Y2 - Magnetic tape no-signal band detection device - Google Patents

Description

[Detailed description of the invention] The present invention is a magnetic tape playback device that selectively plays back a recording band such as a music tape in which a plurality of recording bands are recorded sandwiched between the no-signal bands. This invention relates to a detection device.

Generally, in a no-signal band detection device, when the recording band passes through the head, the output signal is rectified by a rectifier circuit, and the output of the rectifier circuit is used to charge a time constant circuit. When passing, the time constant circuit was discharged, and changes in the output voltage of the time constant circuit were detected to generate a constant pulse.

However, in these devices, the time constant of the time constant circuit is the same during fast forwarding and during playback, so setting a large time constant may shorten the time it takes for the no-signal band to pass through the head, depending on the tape speed during fast forwarding. Even if the no-signal band passes through the head, the next recording band will pass through the head and charge the time constant circuit again before the output voltage of the time constant circuit drops to a certain value, so no pulse will be generated. That happened.

Furthermore, even if the charging voltage drops to a certain value, the time required for the next recording band to pass through the head is too short, and a normal pulse waveform cannot be obtained, resulting in malfunction.

On the other hand, if the time constant of the time constant circuit was set to a small value, the output of the time constant circuit would drop and pulses would be generated in response to very low recording level sections distributed in the recording band during playback. .

The present invention focuses on these problems and makes it possible to change the time constant between fast forwarding and playback.The time constant is set sufficiently small during fast forwarding, while the time constant is set sufficiently large during playback. An object of the present invention is to provide a no-signal band detection device that does not malfunction even during playback.

This will be explained below according to the drawings.

FIG. 1 is a flock diagram of one embodiment of the present invention, in which 1 is a head, and the output of the head 1 is an attenuator 2,
The signal is supplied to a time constant circuit 5 via an amplifier circuit 3 and a rectifier circuit 4.

Furthermore, a voltage limiting circuit 6 is connected to the output end of the time constant circuit 5, and a Schmitt circuit 7 is connected to the output end of the voltage limiting circuit 6.

Attenuator 2 includes resistor 9, resistor 10, and transistor 11
The base electrode of the transistor 11 is connected to a control circuit 8, and a signal from the control circuit 8 causes the transistor 11 to be turned on or off, thereby changing the amount of attenuation.

The time constant circuit 5 is composed of a capacitor 12, a resistor 13, a resistor 14, and a transistor. The base electrode of the transistor 15 is connected to a control circuit 8, and the transistor 15 conducts or cuts off according to a signal from the control circuit 8. The time constant of the constant circuit is designed to change.

The voltage limiting circuit 6 is composed of a constant voltage diode 17, a constant voltage diode 18, and a transistor 19. The base electrode of the transistor 19 is connected to the control circuit 8.
The transistor 19 is turned on or off according to a signal from the control circuit 8, and the voltage limit of the voltage limit circuit 6 is changed.

The control circuit 8 sends a "high" level signal when the tape is running in fast forward mode, and a "low" level signal when the tape is running in the playback state to the base electrodes of the transistors 11, 15, and 19, respectively. and control their operations.

FIG. 2 shows the output waveforms of the button block in the embodiment shown in FIG. , T and T2 are the times when the start and end of the no-signal band pass the head 1, L1 is the limiting voltage of the voltage limiting circuit 6, and τl is the time constant of the time constant circuit 5, respectively.

Also, two. E, H is the amplifier circuit 3 when the tape is running in fast forward.
, are the output waveforms of the time constant circuit 5 and the Schmitt circuit 7, and T3 and T4 are the start and end of the no-signal band when the head 1
VL2 indicates the limiting voltage of the voltage limiting circuit 6, and τ2 indicates the time constant of the time constant circuit 5.

Furthermore, SoN and 5OFF indicate the on level and off level of the Schmitt circuit 7.

In the above embodiment, during reproduction, the output of the control circuit 8 is at a "low" level, and the transistors IL15 and IL19 are in an off state.

Therefore, one end of the attenuator 2, the time constant circuit 5, the resistors 10 and 14 of the voltage limiting circuit 6, and the diode 18 are open, and their attenuation amount, time constant τ1, and limiting voltage vL□ are determined by the resistor 9,
It is determined by a capacitor 12, a resistor 13, and a diode 17.

And Figure 2 A. As shown in (a) and (c), when the starting edge of the no-signal band passes the head 1 at time T1, 11
After the elapse of time, the output level of the time constant circuit 5 reaches the off level 5OFF of the Schmitt circuit 7, and the Schmitt circuit 7
The output of changes to "low" level.

Further, when the end of the no-signal band passes the head 1 at time T2, after a certain period of time has passed from time T2, the output level of the time constant circuit 5 reaches the on level SON of the Schmitt circuit 7, and the output of the Schmitt circuit 7 becomes Return to high level again.

Thus, each time the no-signal band passes through the head 1, the Schmitt circuit 7 generates one pulse.

Next, when the tape runs in fast forward mode, the output of the control circuit 8 is at a "high" level, and the transistors 11, 15, 19
is in the on state.

Therefore, the attenuator 2, the time constant circuit 5, the resistor 10.14 of the voltage limiting circuit 6, and one end of the diode 18 are connected to the transistor 1.
1.15.19 to ground.

Therefore, the attenuation amount of the attenuator 2 increases compared to that during regeneration, the time constant τ2 of the time constant circuit 5 becomes smaller than the time constant r1 during regeneration, and the limiting voltage of the voltage limiting circuit 6 increases due to the diode 17.
．． VL2 is determined by 18.

However, in this case, VL2 is assumed to be smaller than VLt.

As a result, when the starting edge of the no-signal band passes the head 1 at time T3, the output level of the time constant circuit 5 reaches the off level 5OFF of the Schmitt circuit 7 after time τ2 has elapsed from time T3, and the output level of the Schmitt circuit 7 reaches the OFF level 5OFF of the Schmitt circuit 7. changes to "low" level.

Further, when the end of the no-signal band passes the head 1 at time T4, the output level of the time constant circuit 5 reaches the ON level SON of the Schmitt circuit 7 after a certain period of time has elapsed from time T4, and the output of the Schmitt circuit 7 becomes high again. Return to level.

Thus, each time the no-signal band passes through the head 1, the Schmitt circuit I generates one pulse.

As mentioned above, in this invention, the time constant of the time constant circuit is changed during fast forwarding and during playback, so even if the tape running speed becomes somewhat faster during fast forwarding and the time to pass through the no-signal zone becomes shorter, By setting the time constant during fast forwarding to a sufficiently small value, the output voltage of the time constant circuit can be quickly lowered and pulses can be reliably generated.

In addition, even if there are some sections in the signal band where the recording level is very low, by setting the time constant during playback sufficiently large, the output voltage of the time constant circuit for that section can be suppressed and the generation of pulses can be prevented. can.

Further, since the amount of attenuation of the attenuator 2 is changed during fast forwarding and during playback, it is possible to prevent the output level of the head 1 from increasing during fast forwarding and saturating the amplifier circuit 3.

Furthermore, since the limiting voltage of the voltage limiting circuit 6 is changed during fast forwarding and during playback, it is possible to compensate for changes in the impedance of the time constant circuit 5 in accordance with switching of the time constant of the time constant circuit 5.

In general, since the reliability is high as described above, it is possible to provide a no-signal band detection device that does not malfunction even when using a music tape or the like having a wide dynamic range.

[Brief explanation of drawings]

FIG. 1 is a flock diagram of one embodiment of the present invention, and the second
The figure shows the output waveform of the block in the embodiment of FIG. 4... Rectifier circuit, 5... Time constant circuit,
6... Voltage limiting circuit, 7... Schmitt circuit, 8... Control circuit.

Claims (1)

[Scope of utility model registration request] In a no-signal band detection device for a magnetic tape playback device that has a plurality of recording bands sandwiched between no-signal bands, an attenuator that attenuates the output signal of the head and a rectifier that rectifies the output signal from the attenuator. a time constant circuit connected to the output end of the rectifier circuit and charged by the output of the rectifier circuit when a signal band passes through the head and discharged when a no-signal band passes through the head; A voltage limiting circuit that limits an output signal of a time constant circuit, and a Schmitt circuit that detects a change in the output voltage of the voltage limiting circuit, the attenuation of the attenuator, the time constant of the time constant circuit, and the voltage limiting Magnetic tape no-signal band detection device characterized by changing the circuit limit amount during fast forwarding and during playback○