Shock sound prevention circuit

A shock sound prevention circuit comprising:

• an input terminal to which an audio signal, from which DC component is removed, is applied;
• a terminal for reference voltage, a reference voltage at which rises according to turning-on of a power supply;
• a first operational amplifier to which the reference voltage from the terminal for reference voltage is applied as a bias voltage and amplifies the audio signal from the input terminal;
• a second operational amplifier to which the reference voltage from the terminal for reference voltage is applied as a bias voltage and amplifies a reverse signal of the audio signal applied to the first operational amplifier;
• a first buffer to which the reference voltage from the terminal for reference voltage is applied;
• a second buffer to which the reference voltage from the terminal for reference voltage is applied;
• a first output terminal to which an output of the first operational amplifier and an output of the first buffer are connected together;
• a second output terminal to which an output of the second operational amplifier and an output of the second buffer are connected together;
• and
• a control circuit which turns on the first buffer and the second buffer while turns off the first operational amplifier and the second operational amplifier immediately after a turning-on of the power supply,
• wherein DC voltages at the first output terminal and at the second output terminal are varied identically with each other accordingly as the reference voltage varies.

A shock sound prevention circuit comprising:

• a blocking capacitor to remove DC component in an audio signal input;
• a capacitance for reference voltage which is charged upon turning-on of a power supply and generates a reference voltage;
• a first operational amplifier to which the reference voltage from the capacitance for reference voltage is applied as a bias voltage and amplifies an audio signal from the blocking capacitor;
• a second operational amplifier to which the reference voltage from the capacitance for reference voltage is applied as a bias voltage and amplifies a reverse signal of the audio signal applied to the first operational amplifier;
• a first buffer to which the reference voltage from the capacitance for reference voltage is applied;
• a second buffer to which the reference voltage from the capacitance for reference voltage is applied;
• a first output terminal to which an output of the first operational amplifier and an output of the first buffer are connected together;
• a second output terminal to which an output of the second operational amplifier and an output of the second buffer are connected together;
• and
• a speaker connected between the first output terminal and the second output terminal;
• and
• a control circuit which turns on the first buffer and the second buffer while turns off the first operational amplifier and the second operational amplifier immediately after a turning-on of the power supply.