Casio CTK-450 - Filter Block Detailed Schematic; Mute Circuit Detailed Schematic

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Filter Block
Since the sound signal from the CPU is a stepped waveform, the filter block is added to smooth the
waveform.
Mute Circuit
The mute circuit removes noise from the sound signal just before the signal fades away. The circuit
detects amplitude of the decaying sound signal by amplifing it by 1000 times, and transistor T6 flows the
signal into the ground when the amplitude decays almost zero.
MSM6567-15
CPU
To mute circuit
To main volume
Sound signal from filter block
+0.5V at the minimum amplitude (no sound)
-2.7V at the maximum amplitude