JPS5813442Y2 - ALC circuit of stereo tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ALC circuit for a stereo tape recorder having left and right channels.

High-grade tape recorders, generally called tape decks, have means for manually adjusting the recording level, whereas popular tape recorders have a so-called ALC circuit that automatically adjusts the recording level.

The present invention relates to an improvement of a stereo tape recorder having such an ALC circuit, and a conventional example shown in FIG. 1 will be explained.

In FIG. 1, 1 and 2 are input terminals for left and right channels, 3 and 4 are preamplifiers, 5 and 6 are main amplifiers, and 7 and 8 are output terminals.

9 and 10 are the first and second terminals whose collectors and emitters are connected between the signal paths 11 and 12 of the Obukama channel and the ground.
ALC transistors 13 and 14 rectify the signal obtained from the latter stage of the signal path 11.
This is a first and second rectifier circuit that applies a control signal to the LC transistor 9 and the second ALC transistor 10-, and is composed of diodes 15, 16 and capacitors 17, 18.

Resistors 19 and 20 are connected between the rectifier circuits 13 and 14 and the bases of the first and second ALC transistors 9 and 10 in order to set the operating time of the ALC circuit. Between the output terminals, even if the signal obtained from one channel causes the A of the other channel to
The LC circuit is also shorted for operation.

As mentioned above, the ALC of such a stereo tape recorder
Although the circuit was constructed, it had the following drawbacks.

That is, if the characteristics of the first ALC transistor 9 and the second ALC transistor 10 are different, there will be a difference in the compression ratio of the signal level.

As a result, the level of the control signal obtained from a channel with a poor compression ratio becomes higher, and the level of a control signal obtained from a channel with a better compression ratio becomes smaller.

Since the first ALC transistor 9 and the second ALC transistor 10 are controlled by the control signal obtained from the channel having the higher level among both channels, the compression ratio of the ALC transistor with a good compression ratio becomes even better, and the compression ratio increases. The compression ratio of the ALC transistor, which has a poor compression ratio, becomes even worse.

Therefore, the level difference between the signals appearing at the output terminals 7 and 8 of the left and right channels becomes large, and when a tape recorded by such a circuit is played back, a stereo effect cannot be obtained and the listener feels uncomfortable.

The present invention aims to provide an ALC circuit that is improved in this respect, and one embodiment shown in FIG. 2 will be described below.

Components that are the same as those in FIG. 1 are given the same reference numerals.

In the present invention, as shown in the figure, a resistor 21 is inserted and connected between the output terminals of the first rectifier circuit 13 and the second rectifier circuit 14 that constitute the ALC circuit of each channel.

With such a configuration, even if there is a difference in compression ratio due to the difference in characteristics between the first ALC transistor 9 and the second ALC transistor 10, the control signal applied to the ALC transistor of each channel is controlled by the resistor 21. Because of the difference in level, a low-level control signal is applied to the ALC transistor with a good compression ratio, and a high-level control signal is applied to the ALC transistor with a poor compression ratio. As a result, there is no large difference in the compression ratios of the ALC circuits of both nayan channels.

Therefore, when a tape recorded by such a circuit is played back, a sufficient stereo effect can be obtained without causing discomfort to the listener.

The ALC circuit of the present invention has a slightly worse signal level compression ratio than the conventional example shown in Figure 1, and the sound image shifts, but it is about 1 to 2 dB at high input, so it is not audible. It was confirmed that I couldn't feel it at all.

As explained above, the ALC circuit of the present invention eliminates the drawbacks of the conventional circuit with an extremely simple structure, and has great practicality.

[Brief explanation of the drawing]

FIG. 1 shows a conventional ALC circuit, and FIG. 2 shows an embodiment of the ALC circuit of the present invention. Explanation of main drawing numbers, 9... First ALC transistor, 10... Second ALC transistor 11.12... Signal path, 13... First ALC transistor. 1
Rectifier circuit, 14...Second rectifier circuit.

Claims (1)

[Scope of utility model registration request] First and second ALC transistors whose collectors and emitters are connected between the signal path of each left and right channel and the ground, and a signal obtained from the latter stage of the signal path is rectified to An ALC circuit comprising first and second rectifier circuits that apply control signals to the bases of ALC transistors, characterized in that the output terminals of the first and second rectifier circuits are connected to each other via a resistor. ALC circuit of a tossing stereo tape recorder.