Yamaha Corporation

Hajime Asahira

Masao Noro

Hiroyuki Fujita

Kazumasu Tsutsumi

Tomoaki Makino

A protection circuit of a digital amplifier includes a DC voltage detection circuit for detecting a DC voltage occurring in a loudspeaker output terminal; a control circuit for performing protection operation when the DC voltage detection circuit outputs a detection signal; and a midpoint potential detection circuit for detecting midpoint potential shift between a positive power supply voltage and a negative power supply voltage. Output of the midpoint potential detection circuit is connected to input of the DC voltage detection circuit and when the midpoint potential shift is detected, the DC voltage detection circuit outputs a detection signal.

Protection circuit of digital amplifier

Musical sound signal is input to an electronic volume control unit, which in turn adjusts the gain of the input musical signal and outputs the resultant gain-adjusted signal to an amplifier. CPU supplies the electronic volume control unit with a sound volume setting level corresponding to an output of a rotary encoder. At the same time, the CPU generates, with reference to stored data of a ROM table, a hue control signal for changing a displaying hue of a three-color light-emitting diode in accordance with the sound volume setting level supplied by the CPU. The CPU takes in a current sound volume setting level when an upper-limit setting switch is activated, and it retains the taken-in level as an upper limit value of various sound volume setting levels that are to be used to change the displaying hue of the light-emitting diode between purple and red hues. As the sound volume setting level is changed from zero to the upper limit value, the displaying hue changes in a stepwise manner.

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Hamamatsu, Japan

Hajime Asahira