JPH0247621Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a mode switching circuit for a stereo amplifier, and in particular, is intended to prevent changes in the characteristics of a filter connected after the mode switching circuit by mode switching.

Conventionally, most stereo amplifiers are provided with a mode switching circuit for switching between stereo reproduction and monaural reproduction.

Figure 1 is an example of this, where Sa and Sb are the signal sources for the left channel and right channel, respectively.
Each has a voltage source e and an internal impedance R.

Each of the signal sources Sa and Sb is connected to the mode switching circuit 1, and when the switch SW1 is set to the "STELEO" side, the left and right channel signals are output independently to provide stereo operation, and when the switch SW1 is set to the "MONO" side, the left and right channel signals are output independently. ” side, a mixed signal of the left and right channels is output, resulting in monaural operation.

In the figure, _R1 is a mixing resistor.

In the mode switching circuit with the above configuration, when filter circuits such as high-cut filter 2 and low-cut filter 3 are connected to the subsequent stage as shown in the figure, the characteristics of the filters, such as the cut-off frequency, will change during stereo operation and monaural operation. There were flaws that changed.

That is, in the illustrated filter circuit, the cutoff frequency ₁ of the high cut filter 2 during stereo operation is ₁ = R + R ₁ + R 2 + R ₃ /2πC ₁ (R + R ₁ + R ₂ ) R, where R ₃ is the load impedance of the load circuit ₄ . ₃ , and the cutoff frequency ′ ₁ during monaural operation is ′ ₁ = (R+R ₁ )/2+R ₂ +R ₃ /2πC ₁ {(R+R ₁ )/2
It is expressed as +R ₂ }R ₃ and ₁ ≠′ ₁ .

Similarly, the cutoff frequency ₂ of the low cut filter 3 during stereo operation and the cutoff frequency ′ ₂ during monaural operation are ₂ = 1/2πC ₂ (R+R ₁ +R ₂ +R ₃ ) ′ ₂ = 1/2πC ₂ {(R+R ₁ )/2+R ₂ +R ₃ }, and ₂ ≠′ ₂ .

As described above, the conventional mode switching circuit has the drawback that the characteristics of the filters 2 and 3 change between stereo operation and monaural operation.

This idea solves the drawbacks of the conventional example,
This embodiment prevents changes in filter characteristics during mode switching and will be described in detail below.

In Figure 2, Sa and Sb are the left channel and right channel signal sources, respectively, similar to those in Figure 1, and 2, 3, and 4 are the same as the high-cut filter, low-cut filter, and load circuit, respectively, in Figure 1. Since this is a configuration, detailed internal wiring is omitted.

21 is a mode switching circuit in which a series circuit consisting of resistors R ₁₁ and R ₁₂ is connected between the input terminal 21 a and the output terminal 22 a of the left channel, and between the input terminal 21 b and the output terminal 22 b of the right channel, respectively. There is.

SW4 is a pair of interlocking switching pieces 23a and 23b.
The switch has first contacts 24a, 24b connected to the output ends 22a, 22b, respectively, and second contacts 25a, 25b connected to each other.

On the other hand, one switching piece 23a of the switch SW4
is connected to the connection point between the series resistances R ₁₁ and R ₁₂ of the left channel, and the other switching piece 23b is connected to the connection point of the series resistances R ₁₁ and R ₁₂ of the right channel.

Further, the output ends 22a and 22b are each connected to the high cut filter 2.

In the above configuration, when the switching pieces 23a, 23b are connected to the respective first contacts 24a, 24b, the left and right channel signals are independently outputted to the output ends 22a, 22b, thereby providing stereo operation.

On the other hand, the switching pieces 23a and 23b are
When connected to the contacts 25a and 25b, the left and right channel signals are mixed and sent to the output terminals 22a and 22b.
output and exhibits monaural operation.

The cutoff frequencies of filters 2 and 3 in the above operation are ₃ for high cut filter 2 in stereo operation, ' ₃ for monaural operation, 4 for low cut filter 3 in stereo operation, and ₄ for low cut filter 3 in stereo operation. If the cutoff frequency is ′ ₄ , each cutoff frequency is ₃ , ′ ₃ , ₄
，
' ₄ is ₃ = R + R ₁₁ + R ₂ + R ₃ /2πC ₁ (R + R ₁₁ + R ₂ ) R ₃ ' ₃ = (R + R ₁₁ ) / 2 + R ₁₂ + R ₂ + R ₃ /2πC ₁ {(R + R ₁₁
)/2+R ₁₂ +R ₂ }R _{3 4} =1/2πC ₂ (R+R ₁₁ +R ₂ +R ₃ )′ ₄ =1/2πC ₂ {(R+R ₁₁ )/2+R ₁₂ +R ₂ +R ₃ }.

Here, R ₁₁ is adjusted so that R + R 11 = (R + R ₁₁ )/2 + R ₁₂ , that is, R ₁₂ = (R + R ₁₁ ) _/ 2.
By _{choosing the values of}
' ₄ is ₃ = ' ₃ = R + R ₁₁ + R ₂ + R ₃ /2πC ₁ (R + R ₁₁ + R ₂
) R _{3 4} = ' ₄ = 1/2πC ₁ (R + R ₁₁ + R ₂ + R ₃ ), and in both stereo and monaural operation, the high-cut filter cutoff frequency ₃ , ' ₃ and the low-cut filter cutoff frequency ₄ , It is now possible to switch modes without any change in ₄ .

As explained above, this invention is based on the input terminal 21.
Signal sources Sa and Sb are connected to a and 21b, and output ends 22a and 21b are connected to signal sources Sa and Sb.
In the mode switching circuit of a stereo amplifier in which the filter circuits 2 and 3 are connected to the filter circuits 22b and 22b, series-connected resistors R ₁₁ and R ₁₂ are connected between the input terminals 21a and 21b and the output terminals 22a and 22b of the left and right channels, respectively. , the series connected resistor
Interlocking switching pieces 23a, 23b connected to the connection points of _R11 and _R12 , respectively, and output ends 22a, 2
2b respectively connected to the first contacts 24a, 24b.
and a switch SW4 having second contacts 25a and 25b mutually connected to each other, and the resistors R ₁₁ and R ₁₂ are R ₁₂ = (R ₁₁ +R)/2 (where R is the impedance of the signal source). This mode switching circuit is characterized in that it satisfies the following, and can prevent changes in the characteristics of the filter circuits 2 and 3 connected to the subsequent stage during stereo and monaural operation, and prevent changes in playback sound quality due to stereo-monaural switching. It has the advantage of being able to

Although we have described a configuration in which a high-cut filter and a low-cut filter are connected as a filter circuit, it can also be applied to a stereo amplifier equipped with either one of the filters, and of course the same effect can be obtained. The present invention can also be applied to a stereo amplifier equipped with a filter circuit in which the impedance of the signal source and the mixing resistance affect the characteristics of the filter.

[Brief explanation of drawings]

FIG. 1 is a mode switching circuit diagram of a conventional stereo amplifier, and FIG. 2 is a mode switching circuit diagram of a stereo amplifier according to an embodiment of the invention. 21a and 21b are input terminals, Sa and Sb are signal sources, _R11 and _R12 are series connected resistors,
23a, 23b are switching pieces, 24a, 24, respectively.
b is a first contact, 25a and 25b are second contacts, and SW4 is a switch.

Claims (1)

[Scope of utility model registration request] In a mode switching circuit of a stereo amplifier in which signal sources Sa and Sb are connected to input ends 21a and 21b and filter circuits are connected to output ends 22a and 22b, respectively, the input ends 21a and 21b of the left and right channels are respectively connected.
21b and the output terminals 22a, 22b, respectively, and the series-connected resistors _R11 and _R12 , and the interlocking switching pieces 23a, 23b connected to the connection points of the series-connected resistors _R11 and _R12 , respectively, and the output terminals. 2
The first contact 24 connected to 2a and 22b, respectively.
Second contacts 25a, 2 interconnected with a, 24b
5b, and the resistors R ₁₁ and R ₁₂ are R ₁₂ =(R ₁₁ +R)/2
(where R is the impedance of a signal source).