JPH0343681B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crosstalk prevention circuit for a rotary transformer in a VTR.

In recent years, VTRs have become more multi-functional and have changed from 2 heads to 3 heads.
There is a trend towards a four-head system. For example, two heads for normal recording and playback and two heads for special playback.
A 4-head VTR equipped with a 4-head VTR has a head configuration as shown in FIG. ,1
b, 1c, 1d, 2a, 2b, 2c, and 2d.

Therefore, since two adjacent heads in the head configuration shown in FIG. 1 simultaneously reproduce different signals, crosstalk occurs between the windings of the rotary transformer.

The conventional circuit that prevents this crosstalk is
As shown in the figure.

First, during recording, the changeover switch SW is turned to the R side, a DC power source is connected to the collector of the transistor Tr constituting the recording amplifier, and a recording signal is supplied to the base. Therefore, step-up transformer
A recording current flows through the recording side windings of ST ₁ and ST ₂ , respectively, and is supplied to the main heads MA and MB via the rotary transformer RT, and is recorded on the magnetic tape.

Next, during normal playback, the changeover switch SW is turned to the P side, and the playback signal played by the main heads MA and MB is connected to the secondary winding via the rotary transformer RT and step-up transformers _ST1 and _ST2 . It is amplified by reproduction amplifiers 3,3.

Next, during special playback, main heads MA and MB and sub heads SA and SB are used alternately by a head output switching signal.

Here, the subhead during normal playback, the subhead when the main head is used during special playback, and the main head when the subhead is used are shot, respectively.

That is, a switching diode D whose one end is grounded is connected to the reproduction side winding of each step-up transformer, and a short switching signal is used to
A direct current is applied to the reproducing side winding corresponding to the head to be shot. Therefore, since the winding in the rotary transformer RT corresponding to the head when not in use is shorted in an alternating current manner, crosstalk is prevented from occurring.

However, in the conventional circuit described above, a diode is connected to the reproduction side winding of the main head that performs normal reproduction, so this diode
There was a risk that the weak reproduction signal flowing to the reproduction side winding would have adverse effects such as deterioration of the SN ratio and variations in the reproduction output.

The present invention has been made in view of the above points,
To provide a crosstalk prevention circuit for a rotary transformer that does not adversely affect a reproduced signal during normal reproduction.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a circuit diagram of the circuit of this embodiment, and the same parts as in FIG. 3 are given the same figure numbers and their explanations are omitted.

In this embodiment, a diode is not connected to the reproduction side windings of the step-up transformers _ST1 and _ST2 corresponding to the main heads MA and MB, and a short switching signal is supplied to the base of the transistor Tr that constitutes the recording amplifier. Therefore, the main head is shot during special playback.

Therefore, during normal reproduction, subheads SA and SB are shot by passing a shot current through diodes D and D, as in the conventional method. Also,
During special playback (the switch SW is set to the recording side R), when the main head is not in use, the transistor Tr is turned on and the recording side winding is energized to shoot the main head, and when the subhead is not in use, as in the conventional case, The diodes D and D are energized to shoot the subhead.

As described above, according to the present invention, when the main head is switched, it is not done by connecting a switch element such as a diode to the reproduction side winding of the step-up transformer, but by energizing the recording side winding. Since there is no extra element in the side winding, there is no risk of deterioration of the reproduced signal during normal reproduction.

Furthermore, the circuit configuration can be simplified by using the transistors constituting the recording amplifier as switch elements instead of using diodes in the main head short.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the head arrangement of a 4-head VTR, Figure 2 is a sectional view of a rotary transformer used in a 4-head VTR, Figure 3 is a circuit diagram of a conventional rotary transformer crosstalk prevention circuit, and Figure 4. 1 is a circuit diagram of a crosstalk prevention circuit for a rotary transformer according to an embodiment of the present invention. Explanation of main drawing numbers, RT...Rotary transformer,
MA, MB...Main head, SA, SB...Sub head, _ST1 , _ST2 , _ST3 , _ST4 ...Step-up transformer, D...Diode, Tr...Transistor.

Claims (1)

[Scope of Claims] 1. A video tape recorder comprising a pair of recording and reproducing heads and at least one reproducing head, the head being connected to a recording and reproducing circuit via a rotary transformer and a step-up transformer, A switch element is provided in the recording side winding of a step-up transformer connected to a pair of recording and reproducing heads, and during special playback, the switch element is controlled to supply direct current to the recording side winding, so that the step-up transformer is in an unused state. A crosstalk prevention circuit for a rotary transformer, characterized in that a certain recording/reproducing head is shot in an alternating current manner. 2. The crosstalk prevention circuit for a rotary transformer according to claim 1, wherein the switch element also serves as a transistor constituting a recording amplifier.