JPH0452803Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an erasing circuit for supplying an erasing current to an erasing head in a tape recorder for recording analog signals.

(Prior Art) Signals on the tape are erased by passing a current called an erase current of, for example, about 100 KHz through the erase head of a tape recorder. However, if you suddenly apply an erase current to the erase head while the tape is running, or cut off the current erase current, pulse-like noise will be recorded on the tape at the position where the erase current changes. It is known. Therefore, as shown in Japanese Utility Model Application Publication No. 57-38321, in order to reduce this noise, an envelope generator has been installed to gradually raise and lower the erase current. being done.

On the other hand, in a tape recorder, in addition to erasing performed at a normal tape running speed, spot erasing may be required in which erase is performed locally while manually running the tape. The spot erase operation is normally performed as follows. That is, first mark the part you want to erase on the tape and align one end of it with the erase head. Next, the erasing head is operated, and the tape is run by hand by rotating the reel or guide roller until it reaches the other end of the part to be erased. The above is the spot erase method, which is indispensable for professional tape recorders.

(Problem that the invention aims to solve) However, the tape movement speed during spot erase is significantly slower than the normal tape running speed of 7.5 inches per second to 30 inches per second, so the tape moves only a small amount. in spite of,
The rise or fall of the erase current is completed, and when viewed on the tape, the magnetic field suddenly changes at a certain point on the tape. For this reason, conventionally, when spot erasing is performed, there is a problem in that noise occurs when the spot is reproduced at a normal running speed.

To deal with this, it may be possible to lengthen the time constants of the rise and fall of the envelope waveform of the erase current. However, while lengthening the time constants of the rise and fall of the envelope waveform of the erase current is effective in preventing noise generation, in professional tape recorders, the rise and fall time constants at normal tape running speeds are This method cannot be used because the downlink time constant is required to be as short as possible.

The purpose of this invention is to solve the above-mentioned problems and to prevent noise from occurring even when performing spot erase without affecting the rise and fall time constants at normal tape running speeds. The goal is to

[Structure of the invention] (Means for solving the problem) In order to achieve the above object, the erasing circuit of the present invention includes an oscillator that oscillates an erasing signal, and a control voltage applied to the control input terminal that converts the output of this oscillator. a voltage-controlled amplifier that amplifies the signal with a corresponding gain and supplies it to the erase head; a recording envelope generator that has a time constant corresponding to the normal tape running speed; and a recording envelope generator that has a time constant longer than that of the recording envelope generator. It has a spot erase envelope generator, and a control circuit that outputs a recording control signal to the recording envelope generator during normal recording and outputs a spot erase control signal to the spot erase envelope generator during spot erase, The outputs of the recording envelope generator and the spot erase envelope generator were used as the control voltage of the voltage control amplifier.

(Function) Since the present invention has the above configuration, it functions as follows.

In other words, the oscillator that is the signal source for the erase current flowing to the erase head always oscillates, and the gain of the voltage-controlled amplifier is controlled by the control voltage applied to its control input terminal. The magnitude is determined by the control voltage applied to the control input terminal.

During normal recording, a recording control signal is input from the control circuit to the recording envelope generator.
The erase current rises and falls smoothly as the gain of the voltage control amplifier changes depending on the output waveform of the recording envelope generator applied via the selection section. At this time, the envelope generator for spot erase does not operate, so it is not involved in the control of the amplifier.

During spot erase, a spot erase control signal is output from the control circuit to operate only the spot erase envelope generator, and the gain of the voltage control amplifier is controlled by the output applied via the selection section. Since the spot erase envelope generator has a longer time constant than the recording envelope generator, the erase current rises and falls more smoothly than during normal recording.

Therefore, according to the present invention, dedicated envelope generators are provided for normal recording and spot erase, and the rise and fall time constants of the envelope generator for spot erase are set larger than those of the envelope generator for recording. Therefore, it does not affect the rising and falling edges during normal recording, and no noise is generated even when spot erasing is performed.

Furthermore, by having an envelope generator dedicated to spot erase, it is possible to easily configure an erasing circuit with a small number of contacts.

(Example) The illustrated embodiment will be described below.

FIG. 1 is a block diagram showing one embodiment of an erasing circuit according to the present invention.

Reference numeral 1 denotes an oscillator that serves as a signal source for the erase current, and is designed to constantly oscillate at a frequency of, for example, about 100 KHz.

Reference numeral 2 denotes a voltage controlled amplifier (VCA), the gain of which changes depending on the control input voltage input to the control input terminal 6. The oscillator 1 is connected to the input terminal 7 of the VCA 2, and the erase head 3 is connected to the output terminal 8.

11 is a recording envelope generator, 12 is a spot erase envelope generator having a longer time constant than the recording envelope generator 11, and the output of the control circuit 30 is the recording envelope generator 11 and the spot erase envelope generator. It is designed to be input to an envelope generator 12 for use. During normal recording, the control circuit 30 outputs a recording control signal to the recording envelope generator 11,
During spot erase, the spot erase control signal is sent to the spot erase envelope generator 12.
It is now output to . The outputs of the recording envelope generator 11 and the spot erase envelope generator 12 are connected to the anode sides of a diode 13 and a diode 14, respectively. A selection section for selecting the output of the envelope generator 12 is configured. The cathodes of the diodes 13 and 14 are connected to each other and to the control input terminal 6 of the VCA 2.

The operation will be explained below.

The oscillator 1, which is the signal source for the erase current flowing to the erase head 3, is always oscillating, and since the gain of the VCA 2 is controlled by the control voltage applied to its control input terminal 6, the erase current flowing to the erase head 3 The magnitude of the current is determined by the control voltage applied to the control input terminal 6.

During normal recording, a recording control signal is input from the control circuit 30 to the recording envelope generator 11,
The gain of the VCA 2 is changed by the output waveform of the recording envelope generator 11 applied via the diode 13, so that the erase current rises and falls smoothly. At this time, the envelope generator 12 for spot erase does not operate, so the diode 1
4 is turned off, and its output does not participate in the control of amplifier 2.

During spot erase, a spot erase control signal is output from the control circuit 30 and only the spot erase envelope generator 12 operates.
With the output applied via diode 14
The gain of VCA2 is controlled. Since the spot erase envelope generator 12 has a longer time constant than the recording envelope generator 11, the erase current rises and falls more smoothly than during normal recording.

Next, a specific example of an envelope generator is shown in FIG.

The envelope generator generates smooth rising and falling waveforms from a stepwise waveform of a recording control signal or a spot erase control signal.

In FIG. 2, 26 is a control signal input terminal connected to the control circuit 30, and normally has a logic level of H.
It is becoming. When a control signal at logic level L is input from the control circuit 30 to the control signal input terminal 26, the transistor 18 is turned on, and the capacitor 1
5 is charged. Therefore, the voltage across the capacitor 15 rises smoothly according to the time constant determined by the resistor 17 and the capacitor 15, and eventually becomes a constant voltage. The voltage across the capacitor 15 is outputted to the control input terminal 6 of the VCA 2 through a buffer amplifier 27.

Next, when the control signal applied to the control signal input terminal 26 reaches the theoretical level H, the transistor 18
The capacitor 15 is turned off and the charge in the capacitor 15 is discharged to the transistor 19 through the diode 16.
At this time, transistor 19 and transistor 20
The resistor 21 and the resistor 22 constitute a constant current source, and the electric charge of the capacitor 15 is discharged with a constant current, but the capacitor 23 and the resistor 25 are connected when the control signal changes from L to H. At this point, the current value of the current flowing through the transistor 19, that is, the discharge current of the capacitor 15, is temporarily reduced for a short time. Therefore, the capacitor 15 is discharged slowly at first, and after the capacitor 23 is charged, it is discharged with a constant current value, and the capacitor 15 is discharged slowly.
The voltage across 5 falls smoothly.

The rising time constant of the envelope generator described above is determined by the resistor 17 and capacitor 15, and the falling time constant is determined by the current value of the constant current source and capacitor 1.
The recording envelope generator 11 is set to about 100 msec, and the spot erase envelope generator 12 is set to 3 to 10 times that of the recording envelope generator 11.

FIG. 3 shows the output characteristics of the recording envelope generator 11 and the spot erase envelope generator 12, with the vertical axis representing the output voltage and the horizontal axis representing the time. Here, 41 represents the output of the recording envelope generator 11, and 42 represents the output of the spot erase envelope generator 12.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-described embodiment and can be modified as appropriate within the scope of the gist of the present invention.

[Effects of the invention] As detailed above, according to the invention, dedicated envelope generators are provided for normal recording and spot erase, and the rise and fall time constants of the envelope generator for spot erase can be adjusted. Since it is set larger than the recording envelope generator, it does not affect the rise and fall during normal recording, and no noise is generated even when spot erasing is performed.

Furthermore, by having an envelope generator dedicated to spot erase, it is possible to easily configure an erasing circuit with a small number of contacts.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the erasing circuit according to the present invention, Fig. 2 is a circuit diagram of an envelope generator, and Fig. 3 is the output characteristics of the recording envelope generator and the spot erase envelope generator. FIG. 1... Oscillator, 2... Voltage control amplifier, 3...
Erase head, 6...Control signal input terminal, 7...Input terminal, 8...Output terminal, 11...Envelope generator for recording, 12...Envelope generator for spot erase, 13, 14...Diode.

Claims (1)

[Scope of utility model registration request] An oscillator that oscillates an erasing signal in an erasing circuit that supplies erasing current to the erasing head of a tape recorder that has a spot erase function that erases a portion of the signal recorded on a tape by manually moving the tape. a voltage control amplifier which amplifies the output of this oscillator with a gain corresponding to a control voltage applied to a control input terminal and supplies the amplified signal to the erasing head; and a recording envelope generator having a time constant corresponding to the normal tape running speed. and an envelope generator for spot erase which has a longer time constant than the envelope generator for recording, outputs a recording control signal to the recording envelope generator during normal recording, and outputs a spot erase control signal to the spot erase control signal during spot erase. 1. An erasing circuit comprising: a control circuit for outputting to an erasing envelope generator, wherein the outputs of the recording envelope generator and the spot erasing envelope generator are used as control voltages for the voltage control amplifier.