JPS608526B2 - tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape recorder, and in particular to a circuit configuration around the head of the tape recorder. This provides an effective connection configuration for an oscillation circuit.

The recording/playback selector switch in a conventional tape recorder is comprised of a multi-circuit, multi-contact switch, but since this makes the connections very complicated, various research and development efforts have been made to solve this problem. One solution to this problem is to use a recording/playback switch with one circuit and one contact.
A circuit as shown in the figure is proposed. That is, in the figure, 1 is a magnetic head for both recording and playback, 2 is a bias oscillation coil,
3 is a bias oscillation circuit, 4 to 8 are capacitors, and 9 is a recording/playback switch with one circuit and one contact, which is closed during recording and closed during playback. 10' is a power source, 11 is a resistor, 12 is a recording head driving amplifier, 13 is a playback amplifier, and 14 is a microphone.

During playback, if the bias oscillation coil 2 is close to a motor or a built-in speaker (none of which are shown), the coil 2 is likely to receive an induced magnetic field from the motor, etc., and the signal from the coil 2 will be affected by this. is applied to the signal, resulting in deterioration of S/N during reproduction. Therefore, it is conceivable to shield the motor and the oscillation coil 2, but it is not easy to completely perform this shielding. Furthermore, it is preferable to short-circuit the tank circuit of the bias oscillation circuit 3 using a mechanical switch, but this is inconvenient because the number of circuits increases. Therefore, it is conceivable to short-circuit the tank circuit using an electronic switch using a transistor or the like, but this is inconvenient because a direct current flows through the recording/reproducing head 1 and a direct current bias is applied. The present invention provides a circuit configuration that can eliminate the above drawbacks.

Embodiments of the present invention will be described below with reference to FIGS. 2 to 4. In this embodiment, the connection between the tank circuit of the bias oscillator and the recording/reproducing head is changed so that the tank circuit is short-circuited by electronic switching means such as a transistor during reproduction. In the drawings from FIG. 2 onwards, the same components as those in FIG. 1 are designated by the same numbers and their explanations will be omitted. First, Fig. 2 shows the basic circuit configuration, and its characteristic configuration is that one end of the output winding 2a of the bias oscillation coil 2 is grounded, and the end of the output winding 2a of the bias oscillation coil 2 is connected to one end of the recording/playback head. The bias oscillation coil 2 is not interposed between the pond and the reproduction amplifier 13, and the output winding 2a of the bias oscillation coil 2 is connected in parallel with a switch means 15 which is opened during recording and closed during reproduction. be. This switch means 15 is an electronic switching means that is operated in conjunction with the operation of the one-circuit-contact recording/playback selector switch 9, which is closed during recording and is related during playback. Therefore, the specific structure of this switching means 15 will be explained using FIG. 3.

Output winding 2 of recording/playback head 1 and bias oscillation coil 2
A series circuit of a first diode 16 and a second diode 17 is connected between the connection point with a and the ground. At this time, the first and second diodes 16 and 17 are connected in series with the same pole, for example, the anode side in the embodiment, facing each other. The connection point 18 between the first and second diodes 16 and 17 is p
The collector and emitter of the np transistor 19 are connected to the positive side of the DC power supply 10 via a resistor 20. The base of the transistor 9 is grounded via a resistor 21 and connected to the power source 1 via a recording/playback switch 9.
Connected to the positive side of 0. The operation of the above embodiment will now be explained. First, during playback, the recording and playback switch 9 is open as shown in the figure, so power is not supplied to the bias oscillation circuit 3 and the bias oscillation circuit 3 is not operated.

At this time, no power supply voltage is applied to the base of the transistor 19, and voltage is applied across the two resistors between the base and emitter of the transistor 19, so the transistor becomes conductive and the first and second diodes 16 , 17 are made conductive. If the daily direction resistances of these two diodes 16 and 17 are kept sufficiently small, both ends of the output winding 2a of the oscillation coil 2 of the oscillation circuit 3 are short-circuited through a resistance of several o. Therefore, a motor is placed near this oscillation coil 2.
Even if a speaker or the like is provided, a magnetic field will not be induced into the coil 2 by the motor or the like and supplied to the head, and the S/N of the signal reproduced from the head 1 will not be affected. On the other hand, during recording, the recording/playback selector switch 9 is closed, so the bias oscillation circuit 3 is powered and operated, sends a bias oscillation signal to the head 1, and receives the recording signal sent from the microphone 14 via the amplifier 12. Can be recorded on tape using the AC bias method. At this time, since the power supply voltage is also applied to the base of the transistor 19, the base-emitter voltage of the transistor 19 becomes almost zero, and the transistor 19 becomes non-conductive. Therefore, the connection point 18 of diodes 16, 17
The supply voltage is no longer supplied to the diodes, and these diodes become non-conducting. This non-conducting state of the diode is not compromised by the bias oscillation signal. In other words, the bias oscillation signal generally has a frequency of several tens of kilohertz,
Although the amplitude is about 10Vp-p, the positive amplitude of this signal (about 0.5V) is due to the reverse breakdown voltage of the diode 16 (
30~35V) Forward voltage of diode 17 (0.7
V), the non-conductive state of the diodes 16 and 17 is maintained. On the other hand, the negative amplitude of the bias oscillation signal (approximately 0.5V) is equal to the reverse withstand voltage of the diode 17 (30 to 35V) + the forward voltage of the diode 16 (0.5V).
7V) or Vc8 of transistor 9. (10-25
V)+, whichever is lower of the forward voltage of diode 16, the non-conducting state of diodes 16 and 17 is maintained. Therefore, the bias oscillation signal from the bias oscillation circuit 3 is supplied to the head without being attenuated.
Although it is possible to use a type transistor and take advantage of its diode characteristics, since the reverse breakdown voltage between the base and emitter of the transistor is about 7V, it is effective if the amplitude of the bias oscillation signal can be set small.

FIG. 4 shows another example of the configuration of the switching means 15, in which the connection point 18 between the first and second diodes 16 and 17 is connected to
The collector of the PNP transistor 22 whose base is grounded is connected to the collector of the NPN transistor 23 whose emitter is grounded via the collector emitter of the PNP transistor 22 whose base is grounded.
connected to terminal B connected to the positive side of power supply 10 via
The base of the transistor 23 is connected to a terminal C connected to the recording/playback switch 9 via a resistor.

It goes without saying that similar effects can be obtained with the circuit shown in FIG. The switching means 15 shown in FIGS. 3 and 4 has the advantage that it can be easily integrated into an integrated circuit, but in any case, no direct current flows through the head 1 during recording, which impedes the alternating current bias. Never.

As explained above, according to the tape recorder of the present invention, the supply and cutoff of bias signals to the recording/playback head can be controlled using a single circuit/contact recording/playback switch.
Moreover, it is possible to prevent the S/N of the reproduced signal from decreasing due to the induced magnetic field of the oscillation coil during playback, and this can be achieved without causing the problem of supplying direct current to the head during recording, and its practical effects. is large.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a tape recorder developed prior to the present invention, Fig. 2 is a basic circuit diagram of a tape recorder according to an embodiment of the present invention, Fig. 3 is a specific circuit diagram of the same tape recorder, and Fig. 4 FIG. 2 is a circuit diagram showing another embodiment of the switching means. 1... Recording/playback head, 2... Bias oscillation coil, 3... Bias oscillation circuit, 9...
... Recording/playback selection switch, 15... Switching means, 16, 17... Diode, 19? 22
, 23...transistor. Machine 1 Figure 2 Figure Shizuka 8 Sardine and Leopard 4 Figure

Claims (1)

[Claims] 1 One end of the output winding of the bias oscillation circuit is grounded, the other end of the winding is connected to the recording/playback head, and a switch means is connected in parallel to the output winding, which is opened during recording and closed during playback. The switching means includes a series circuit of first and second diodes connected in parallel to the output winding of the bias oscillation circuit and in opposite directions to each other;
and a current-carrying control transistor whose output terminal is connected to the connection point of the second diode, and by inputting a signal to the input terminal of the current-carrying control transistor in accordance with recording or playback, the switching means is operated. A tape recorder characterized in that it is configured to allow