JPH07274388A - Changeover circuit of power-supply voltage of amplifier for audio - Google Patents

Abstract

PURPOSE:To change over the driving voltage of an amplifier part according to the number of loudspeaker systems, to be driven, without increasing the number of contact circuits for loudspeaker switches. CONSTITUTION:A low-pass filter 62 is connected to OFF-fixed contacts 28a, 30a for loudspeaker switches 27, 29. The cutoff frequency of the low-pass filter 62 is set at an audio band or lower. When the loudspeaker switches 27, 29 are both turned on, the input of the low-pass filter 62 is set to a floating state, a capacitor C1 is discharged, a relay 48 is turned on, and relay contacts 16, 17 are connected to the side of a low voltage. When only one out of the loudspeaker switches 27, 29 is turned on, the capacitor C1 for the low-pass filter 62 is charged, the relay 48 is turned off, and the relay contacts 16, 17 are changed over to the side of a high voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in an audio amplifier having a speaker switching function for independently driving or parallel driving a plurality of speaker systems for the same signal source, switches the power supply voltage in accordance with the number of driven systems. For the circuit.

[0002]

2. Description of the Related Art Audio amplifiers (pre-main amplifiers, power amplifiers, etc.) are generally constructed so that a plurality of speaker systems can be connected, and they are driven individually or simultaneously according to the operation of a speaker changeover switch. It can be driven. In the past, this switching was performed by simply switching the connection between the amplifier output and the speaker system by using the speaker switching switch.

However, when switching and driving a plurality of sets of speaker systems in this manner, it is necessary to pay attention to the load condition viewed from the amplifier side. That is, when the speaker is driven independently, the load becomes 8Ω, and when two speakers are driven in parallel, the load becomes 4Ω. In the amplifier catalog,
Generally, it is displayed as how many W output with 8Ω load and what W output with 4Ω load, and it is designed so that the performance is tentatively guaranteed within the allowable load range. However, the smaller the load, the more severe the condition for the amplifier. For example, if a current of 1 A flows through the power transistor with an 8 Ω load that drives the speaker independently, a current of 2 A will flow with a 4 Ω load that drives two speakers in parallel. As described above, as the number of parallel units increases, the load value decreases, and a large current flows through the power transistor, causing heat generation, which may damage the power transistor in the worst case.

Therefore, in order to solve such a problem, the power supply voltage of the amplifier is increased during the independent drive and lowered during the parallel drive in association with the switching between the independent drive and the parallel drive of the speaker. Conventionally, the drive current has been reduced.

FIG. 2 shows a conventional amplifier having such a variable power supply voltage configuration. In FIG. 2, only one of the left and right channels is shown, and the other channel is similarly configured. In the audio amplifier 1, the power supply circuit 10 supplies the commercial AC power supply 12 to the primary winding 18a of the power transformer 18. The secondary winding 18b of the power transformer 18 has a center tap C and a +
Two high and low taps H ⁺ ,
L ⁺ , H ⁻ , and L ⁻ are provided. The center tap C is grounded. The output voltages of the + side taps H ⁺ , L ⁺ and the − side taps H ⁻ , L ⁻ are rectified by the rectifier circuit 20 via the relay contacts 16 and 17 of the voltage switching relay 48 and smoothed by the capacitors 22 and 24. , DC voltage + B, -B
Is obtained and is supplied to the amplifier section 26 as a power source. The amplifier unit 26 amplifies the audio signal and supplies it to the speaker terminals 32 and 34 from the speaker on / off contacts 28 and 30 of the A and B system speaker switches 27 and 29 through the speaker output circuits 33 and 35. . Speaker terminal 3
2, 34 are speakers 36 of A system and B system,
38 is connected.

The speaker on / off contacts 28 and 30 have four types of speaker output connection states, that is, both the A and B systems are off, only the A system side is independently driven, only the B system side is independently driven, and the A and B systems are concurrently driven. Push button 40, 4 provided independently on the A system side and the B system side, respectively.
It is turned on and off by the operation of 2.

The speaker switches 27 and 29 are provided with voltage switching contacts 44 and 46 which are turned on and off in conjunction with the speaker on and off contacts 28 and 30. These voltage switching contacts 44 and 46 are connected in series between the + B power source line and the ground. The relay coil 50 and the resistor 52 of the voltage switching relay 48 are inserted in this series circuit. The voltage switching relay 48 is
When the relay coil 50 is not excited, the relay contacts 16 and 1
7 is connected to the high voltage side H ⁺ , H ⁻ , and the relay coil 50
When is excited, the relay contacts 16 and 17 are connected to the low voltage side L ⁺ and L ⁻ .

The operation of the circuit of FIG. 2 is as follows. Push button 40 (A system) off, push button 4
When 2 (B system) is turned on, the speaker on / off contact 28 is off, the speaker on / off contact 30 is on, and only the speaker 38 on the B system side is driven. At this time, since the voltage switching contacts 44 and 46 are turned off, the relay coil 50 of the voltage switching relay 48 is not excited and the relay contacts 16 and 17 have high voltages H ⁺ and H.
^- is connected to the side, the amplifier unit 26 is driven at a higher voltage.

When the push button 40 (A system) is on and the push button 42 (B system) is off, the speaker on / off contact 28 is on, the speaker on / off contact 30 is off, and A Only the speaker 36 on the system side is driven. At this time, the voltage switching contact 4
Since the contacts 46 of the relays 4 and 46 are turned off, the relay coil 50 of the voltage switching relay 48 is not excited and the relay contacts 1
6, 17 are connected to the high voltage H ⁺ , H ⁻ side, and the amplifier section 26 is driven at a high voltage.

When the push buttons 40 and 42 are both turned on, the speaker on / off contacts 28 and 30 are turned on.
Are both turned on, and both the A and B system speakers 36,
38 are driven in parallel. At this time, the voltage switching contact 4
Both relays 4 and 46 are turned on, which causes the relay coil 5
0 is excited and the relay contacts 16 and 17 are on the low voltage side L
^+, L ^- to be connected, the amplifier unit 26 is driven at a low voltage. Therefore, it is possible to prevent a large current from flowing through the amplifier unit 26 and prevent damage due to overheating.

[0011]

In order to realize the circuit configuration shown in FIG. 2, speaker switches 27 and 29 are provided as compared with a conventional audio amplifier which does not have a power supply voltage switching function.
It was necessary to increase the number of contact circuits of each one by two to make two contacts, which resulted in high cost.

According to the present invention, the number of contact circuits of a speaker switch is increased when the problem in the conventional technique is solved and a function of switching the drive voltage of the amplifier unit according to the number of driven speaker systems is provided. It aims to provide a power supply voltage switching circuit for an audio amplifier that realizes this.

[0013]

The invention according to claim 1 is
A power supply circuit that outputs a power supply voltage with a variable voltage value, and a circuit that inputs an audio signal and amplifies the audio signal using the power supply voltage output from the power supply circuit, depending on the magnitude of the power supply voltage. An amplifier section with variable output power, a speaker output circuit installed in parallel on the output side of the amplifier section, a movable contact on the input side, and an ON fixed contact and an OFF fixed contact on the output side In this state, the speaker output circuits of the respective systems are respectively inserted, and speaker on / off means for individually turning on / off the respective systems according to an external operation and a cutoff frequency are set to be equal to or lower than the audio band. The low-pass filter that inputs the signal introduced to the OFF fixed contact of the speaker ON / OFF means of the system in common or individually, and the output level of this low-pass filter. The speaker switch to determine whether only one system is on or two or more systems are on. When only one system is on, the output voltage of the power supply circuit is increased to turn on two or more systems. In this case, a power supply voltage control means for lowering the output voltage of the power supply circuit is provided.

According to a second aspect of the present invention, a power supply circuit that outputs a power supply voltage so that the voltage value can be switched between at least two levels of high and low, and an audio signal is input, and the power supply voltage output from the power supply circuit is used. A circuit for amplifying the audio signal, in which the output power changes according to the magnitude of the power supply voltage, a speaker output circuit provided in parallel with two lines on the output side of the amplifier unit, and a movable contact input Speaker on circuit which is placed on the output side and is inserted into the speaker output circuits of the two systems in a state where the fixed on-contact and the fixed off-contact are arranged on the output side and individually turns on and off the respective systems according to an external operation. , OFF means and a low-frequency cutoff frequency set to be equal to or lower than the audio band, and a signal to be commonly input to the OFF fixed contacts of the two-system speaker ON / OFF means. The output voltage of the power supply circuit when only one system is turned on or both systems are turned on by the output level of the low-pass filter and the output filter. And a power supply voltage control means for lowering the output voltage of the power supply circuit when both systems are turned on.

According to a third aspect of the present invention, the control output of the power supply voltage control means controls the lighting of an indicator that indicates whether the number of systems in which the speaker on / off means is on is one or two or more. It is also characterized in that it is also used for variable control of the operating voltage of the speaker protection circuit.

[0016]

According to the invention of claim 1, the speaker is turned on,
In the OFF means, the signal of the OFF fixed contact, which has not been used conventionally, is input to the low-pass filter whose cut-off frequency is equal to or lower than the audio band, and whether the speaker switch turns on only one system according to the output level of this low-pass filter. Since it is determined whether two or more lines are on and the power supply voltage for driving the amplifier is switched,
The power supply voltage can be switched without increasing the number of contact circuits of the speaker switch.

According to the second aspect of the present invention, in a general audio amplifier having two speaker output systems, one system is used and two systems are used. The power supply voltage can be switched between high and low stages without increasing the number of switch contact circuits, and the low-pass filter can be shared by two systems.

According to the third aspect of the present invention, the control output of the power supply voltage control means is controlled to light an indicator for displaying whether the number of systems in which the speaker on / off means is on is one or two or more. Since it is also used for variable control of the operating voltage of the speaker protection circuit, lighting control of the indicator or variable control of the operating voltage of the speaker protection circuit can be performed without increasing the number of contact circuits of the speaker switch.

[0019]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, only one of the left and right channels is shown, and the other channel is similarly configured.
In the audio amplifier 60 (pre-main amplifier, power amplifier, etc.) in FIG. 1, the power supply circuit 10 supplies the commercial AC power supply 12 to the primary winding 18 a of the power transformer 18. Power to the secondary winding 18b of the transformer 18, the midpoint tap C and + side, - high and low two taps H ⁺ for side respectively, L ^+, H ^-, L ^- is provided. The center tap C is grounded. + Side tap H ⁺ , L ⁺
The output voltage of the − side taps H ⁻ and L ⁻ is rectified by the rectifier circuit 20 via the relay contacts 16 and 17 of the voltage switching relay 48.
Is rectified and smoothed by the capacitors 22 and 24 to obtain DC voltages + B and −B, which are supplied to the amplifier unit 26 as a power source.

The amplifier section 26 power-amplifies the audio signal to produce speaker switches 27 and 29 for A and B systems.
From the speaker output circuit 33, 35 to the speaker terminals 32, 34. Speakers 32 and 34 are connected to speakers 36 and 38 of A system and B system, respectively.

The speaker switches 27 and 29 switch the speaker connection state between the A and B systems off, the A system side alone drive, the B system side alone drive, and the A and B system parallel drive. , A system side and B system side are independently turned on and off by operating push buttons 40 and 42 (each time they are pressed, they are locked on or locked off). Speaker switch 27,2
9, the movable contacts 28c and 30c are arranged on the input side, and the ON fixed contacts 28b and 30b and the OFF fixed contacts 28a and
30a is arranged on the output side.

Resistors R2 and R3 are provided between the OFF fixed contacts 28a and 30a of the speaker switches 28 and 30 and the negative power source-B.
And a low-pass filter 62 including a capacitor C1 are commonly connected. The low-pass filter 62 has a cutoff frequency lower than the audio band (for example, 1).
0 Hz) is set.

The output of the low pass filter 62 (voltage of the capacitor C1) is input to the power supply voltage control circuit 64. The power supply voltage control circuit 64 turns on and off the voltage switching relay 48 according to the output of the low-pass filter 62.
It comprises transistors Q1 and Q2. Transistor Q
In No. 1, the collector is connected to the power supply + B via the resistors R4 and R5, the emitter is connected to the power supply -B, and the output voltage of the low pass filter 62 is applied between the base and the emitter. The transistor Q2 has a collector connected to the power supply + B via the relay coil 50 of the voltage switching relay 48 and the resistor R6, an emitter grounded, and a base connected to an intermediate point between the resistors R4 and R5. A diode D1 is connected between the emitter and the base for protection against a reverse voltage.

The voltage switching relay 48 comprises the relay coil 5
When 0 is non-excited, the relay contacts 16 and 17 are connected to the high voltage sides H ⁺ and H ⁻ , and when the relay coil 50 is excited, the relay contacts 16 and 17 are connected to the low voltage sides L ⁺ and L ⁻ . . When the relay coil 50 is excited, the relay contact 61 is turned on and the indicator lamp 63 is turned on to display that both systems A and B are being driven. Also,
It also switches the operating voltage of the speaker protection circuit.

The operation of the circuit of FIG. 1 is as follows. Push button 40 (A system) off, push button 4
When the 2 (B system) is turned on, the speaker switch 2
7, the speaker switch 29 is turned on, and only the speaker 38 on the B system side is driven. At this time, in the low-pass filter 62, the OFF fixed contact 28a of the speaker switch 27 is connected to the movable contact 28c, so that the capacitor C1 is charged. As a result, in the power supply voltage control means 64, the transistor Q1 is turned on. When the transistor Q1 is turned on, the potential at the intermediate point between the resistors R4 and R5 becomes negative, the diode D1 is turned on and the transistor Q2 is turned on.
Is turned off. Therefore, the relay coil 50 of the voltage switching relay 48 is not excited, the relay contacts 16 and 17 are connected to the high voltage H ⁺ , H ⁻ side, and the amplifier section 26 is driven at the high voltage.

When the push button 40 (A system) is turned on and the push button 42 (B system) is turned off, the speaker switch 27 is turned on and the speaker switch 2 is turned on.
9 is turned off, and only the speaker 36 on the A system side is driven. At this time, in the low-pass filter 62, the OFF fixed contact 30a of the speaker switch 29 is connected to the movable contact 28c, so that the capacitor C1 is in a charged state. As a result, the power supply voltage control means 64 causes the transistor Q1
Turns on. When Transitus Q1 turns on, resistance R
The potential at the midpoint between 4 and R5 becomes negative, the diode D1 turns on and the transistor Q2 turns off. Therefore,
The relay coil 50 of the voltage switching relay 48 is not excited, the relay contacts 16 and 17 are connected to the high voltage H ⁺ , H ⁻ side, and the amplifier section 26 is driven at a high voltage.

When the push buttons 40 and 42 are both turned on, the speaker switches 27 and 29 are both turned on, and the speakers 36 and 38 of both the A and B systems are driven in parallel. At this time, the low pass filter 62
OFF fixed contacts 28a, 3 of the speaker switches 27, 29
Since both 0a are in a floating state, the capacitor C1 is in a discharging state. Therefore, the transistor Q
1 turns off and transistor Q2 turns on. As a result, the relay coil 50 is excited and the relay contacts 16, 17
Is connected to the low voltage side L ⁺ , L ⁻ , and the amplifier section 26 is driven at a low voltage. Therefore, it is possible to prevent a large current from flowing through the amplifier unit 26 and prevent damage due to overheating. At this time, the indicator lamp 6
When 3 is turned on, the operating voltage of the speaker protection circuit is also switched.

In FIG. 1, the resistor R1 prevents the power supply voltage control circuit 64 from malfunctioning due to the operation of the relay contact 70 of the protection relay inserted between the amplifier section 26 and the speaker switches 27 and 29. It is for. That is, when the resistor R1 is not provided, when only one system of A or B is turned on (the power supply voltage is high), the protection circuit operates and the relay contact 70 is turned off. In the floating state, the capacitor C1 is discharged, Q1 is turned off, Q2 is turned on, the relay coil 50 is excited, and the relay contact 16,
17 is switched to the low voltage L ⁺ , L ⁻ side. On the other hand, by inserting the resistor R1, the relay contact 7
Even when 0 is turned off, the input of the low-pass filter 62 does not enter the floating state, and the power supply voltage can be maintained at a high voltage.

As described above, according to the circuit of FIG. 1, the speaker switches 27 and 29 can switch the power supply voltage while the number of contact circuits is one. In this case, the resistors R1 to R5, the capacitor C1, the diode D1, and the transistors Q1 and Q2 are additionally required as compared with the conventional circuit of FIG. 2, but the cost is significantly increased even if the number of circuits of the switch is increased by one. (These elements R1 to R5, C
(It is much more expensive than the total cost of 1, D1, Q1, and Q2), and the effect of being able to reduce the number of switch circuits is very large.

In each of the above embodiments, the case of switching two sets of speakers has been described, but the present invention can be applied to the case of switching three or more sets of speakers. In this case, if the number of parallel drives is two or more, a predetermined low voltage is uniformly applied, and the power supply voltage can be sequentially switched according to the number of parallel drives (the voltage decreases as the number of parallel drives increases). Further, the low-pass filter can be individually provided for each system.

Further, in each of the above-mentioned embodiments, the speaker switches 27, 29 are of a type driven by push buttons provided for each speaker, but various switching means such as a rotary switch type can be used. Also, the voltage switching is
It can also be performed on the primary winding 18a side of the transformer 18.

[0032]

As described above, according to the first aspect of the present invention, in the speaker on / off means, the signal of the fixed OFF contact which has not been used conventionally is low-passed with the cut-off frequency lower than the audio band. By inputting to the filter, the output level of this low-pass filter is used to determine whether the speaker switch is turned on in only one system or in two or more systems, and the power supply voltage for driving the amplifier is switched. The power supply voltage can be switched without increasing the number of contact circuits of the speaker switch.

According to the second aspect of the invention, in a general audio amplifier having two speaker outputs, one system is used and two systems are used. The power supply voltage can be switched between high and low stages without increasing the number of switch contact circuits, and the low-pass filter can be shared by two systems.

According to a third aspect of the present invention, the control output of the power supply voltage control means is controlled by lighting an indicator for displaying whether the number of systems in which the speaker on / off means is on is one or two or more. Since it is also used for variable control of the operating voltage of the speaker protection circuit, lighting control of the indicator or variable control of the operating voltage of the speaker protection circuit can be performed without increasing the number of contact circuits of the speaker switch.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional device.

[Explanation of symbols]

10 power supply circuit 26 amplifier section 27, 29 speaker switch (speaker on / off means) 28a, 30a OFF fixed contact 28b, 30b ON fixed contact 28c, 30c movable contact 33, 35 speaker output circuit 60 audio amplifier 62 low pass filter 64 power supply Voltage control circuit (power supply voltage control means)

Claims (3)

[Claims] 1. A power supply circuit that outputs a power supply voltage with a variable voltage value, and a circuit that inputs an audio signal and amplifies the audio signal using the power supply voltage output from the power supply circuit. An amplifier section whose output power changes depending on the voltage level, a speaker output circuit that is installed in parallel with multiple lines on the output side of this amplifier section, and a movable contact are arranged on the input side. The speaker on / off means that is inserted into the speaker output circuit of each system in the state of being placed on the output side and turns on / off each system individually according to the external operation, and the cutoff frequency is below the audio band. A low-pass filter that inputs a signal that is set and is introduced to the OFF fixed contact of the speaker ON / OFF means of each system in common or individually; According to the output level of the filter, it is determined whether the speaker switch is on only one system or more than two systems, and when only one system is on, the output voltage of the power supply circuit is increased to set two systems. A power supply voltage switching circuit for an audio amplifier, comprising power supply voltage control means for lowering the output voltage of the power supply circuit when it is on. 2. A power supply circuit that outputs a power supply voltage so that the voltage value can be switched between at least two levels, high and low, and an audio signal is input, and the audio signal is amplified using the power supply voltage output from the power supply circuit. An amplifier unit whose output power changes according to the magnitude of the power supply voltage, a speaker output circuit provided in parallel with two lines on the output side of the amplifier unit, and a movable contact on the input side to turn on the circuit. A speaker ON / OFF means that is inserted into the speaker output circuits of the two systems with the fixed contact and the OFF fixed contact arranged on the output side, and that individually turns on and off each system according to an external operation, and cut A low-pass filter having an off frequency set to be equal to or lower than an audio band and commonly inputting a signal led to an off fixed contact of the two-system speaker on / off means; The output level of the low-pass filter is used to determine whether only one system or two systems are turned on for the speaker switch, and when only one system is turned on, the output voltage of the power supply circuit is increased to 2 A power supply voltage switching circuit for an audio amplifier, comprising power supply voltage control means for lowering the output voltage of the power supply circuit when both systems are turned on. 3. The control output of the power supply voltage control means is a lighting control of an indicator for indicating whether the number of systems in which the speaker on / off means is on is one or more, or an operating voltage of a speaker protection circuit. 3. The power supply voltage switching circuit for an audio amplifier according to claim 1, wherein the power supply voltage switching circuit is also used for variable control.