JPH0132412Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit for an audio amplifier.

Conventionally, as a countermeasure against shock noise when powering on an amplifier, various delay circuits have been used to delay the timing of applying the power supply voltage to the preamplification stage from the time of application of the power supply voltage to the power amplification stage when the power is turned on. is being carried out. For example, as shown in Figure 1a, the application of the power supply voltage to the preamplifier stage 1 is
As shown in FIG. 1b, a mute signal delayed by time _t0 from the power-on at time t is applied to the base of transistor 2, and The application of the power supply voltage to the power amplification stage 1 is delayed by t ₀ time from the timing of application of the power supply voltage to the power amplification stage 3.

However, when using the conventional amplifier as described above, if a negative signal is applied to the input of the preamplifier stage 1 within the period from time t to time _t0 shown in FIG. The base current _i
flows. Therefore, the collector current _ic flows through the first stage transistor 5, and shock noise is generated.
This type of shock noise, for example at the level of the equalizer stage, far exceeds the sensitivity level, causing the power amplification stage 3 to swing to full swing and possibly damaging the speaker.

For this purpose, in addition to the muting circuit using the transistor 2, a transistor 6 is connected in parallel to the input terminal of the power amplification stage 3, and a muting signal as shown by the broken line in FIG. A positive spike voltage that rises when voltage is applied is applied to the base of the second transistor 6 to prevent the above-mentioned shock noise.

However, when this method is used, not only is a muting circuit made up of transistor 6 required in addition to the muting circuit made up of transistor 2, but also two sets of muting circuits made up of transistor 6 are required in the case of stereo signal amplification. There were flaws.

The present invention has been made in view of the above, and it is an object of the present invention to provide a muting circuit which eliminates the above-mentioned drawbacks with a simple configuration.

The present invention will be explained below using examples.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

In FIG. 2, the same components as in FIG. 1a are designated by the same reference numerals.

In one embodiment of the present invention, the transistor 6 is removed from the circuit shown in FIG. 1a, and a diode 7 is connected between the capacitor 4 constituting the ripple filter for the first stage of the amplifier and the ground. Furthermore, a resistor 9 is connected between the common connection point of the diode 7 and the capacitor 4 and one end of the resistor 8 constituting the ripple filter, and a predetermined value after the muting by the transistor 2 is released from t when the power is turned on to the amplifier is connected. The diode 7 is set to be turned on when the time is exceeded.

In this embodiment configured as described above, a voltage having a waveform as shown in _FIG. Delayed preamplifier stage 1
Power supply voltage is applied to. That is, the transistor 2 is in an off state for a period of time _t0 from the power-on time t.

However, even if a negative signal is applied to the input of the preamplifier stage 1 during this period, since the diode 7 is connected in series with the capacitor 4, the broken line in FIG. The base current i _b of the transistor 5 shown does not flow. Therefore, even if the power supply voltage is already applied to the power amplification stage 3, no shock noise is generated, and there is no need to provide the transistor 6.

Further, when the time t ₀ has passed since the power-on time t, the transistor 2 is turned on and the power supply voltage is applied to the preamplifier stage 1. Since the transistor 2 is turned on, the diode 7 is connected to the resistor 9.
After a set time determined by the resistance value of the resistor 9 through the resistor 9, it becomes on state. Therefore, diode 7
The capacitor 4 is grounded through the capacitor 4, and the ripple filter functions normally.

As described above, according to this embodiment, only one switch element and one resistor are added to the conventional circuit, and the first
There is no need to separately provide a transistor 6 for muting as shown in FIG.

In addition, in the above embodiment, the case where the input stage of the amplifier is a PNP transistor was explained as an example.
The same applies to NPN transistors.

As explained above, according to the present invention, the drawbacks of the conventional circuit can be solved with an extremely simple configuration, and the number of parts for this purpose can be reduced and the configuration can be made at low cost.

[Brief explanation of the drawing]

FIG. 1a is a circuit diagram of an amplifier using a conventional muting circuit. FIGS. 1b and 1c are diagrams showing mute signal waveforms in the circuit shown in FIG. 1. Second
The figure is a circuit diagram of one embodiment of the present invention. 1... Preamplification stage, 3... Power amplification stage, 4...
A capacitor forming a ripple filter for the first stage of the amplifier, 5... first stage transistor, 7... diode, 9... resistor.

Claims (1)

[Scope of utility model registration request] a unidirectional element connected in series with a capacitor constituting a ripple filter for an amplification stage in the first stage of an amplifier and for cutting off the capacitor from the circuit; 1. A muting circuit characterized by comprising: a conduction means for maintaining a switching element in an on state.