Circuit Descriptions - Pioneer GM-D505 Service Manual

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7.3 CIRCUIT DESCRIPTIONS

- The principle of class-D amplifier.
A class-D amplifier uses (Pulse Wide Modulation) PWM . This means that the original signal Vin(sine-waved signal) at
the input is modulated with another signal Vm which has a much higher fixed frequency. The waveform which is used
as carrier wave or modulation signal is normally a triangle-shaped signal.
Vin: input signal (sine-waved signal)
Vm: modulated signal (triangle-shaped signal)
Vd: output signal (pulse width modulated signal)
The Vd signal has a fundamental frequency equal to that of the modulation frequency Fm (the frequency of the modu-
lation signal Vm) but will also contain the input signal and a band of frequency components around the modulation
frequency.
The original signal Fvin is selected with a low pass filter, cutting the high frequencies around the modulation frequen-
cy Fm.
Fvin: original signal
Fc: cut off frequency
Fm: modulation frequency
- Circuit Description
IC401 (TDA7570) is class D Chip with internal Analog to Digital Converter. (See an IC information block)
IC401 (TDA7570) digitizes the analog waveform and uses PWM at 310kHz Rail to Rail Square wave to generate an
audio signal that is then recovered by the 4th order LC filter.
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GM-D505/XH/EW
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