through PT 2399 (N204), it is sent to power amplifier board for small signal amplifying through band-
Pass filter. PT 2315 is controlled by MCU, so users may adjust his desired Karaoke effect at will through
remote controller.
Another path signal, after amplifying rectification, controls a switch triode V201 9014 to control the
high/low level of detect signal P-KT to fulfil the detecting of Karaoke signals. When the inputted Karaoke
signal is large enough, the DC after being rectified makes triode V201 on and then pulls down P-KT
signal, which means that there is Karaoke signal input. Now, KM control signal is low level, triode V101
2N5401, V102 S8050 both cut off, Karaoke signals enter IC N107 NE5532 for amplifying through
coupling capacitor C147, C149, then they are sent to left/right channel; when CPU cannot detect signals
in a certain period, P-KT is high level, now KM control signal of CPU changes into high level, triode
V101, V102 are both on to make Karaoke signal short circuit to ground, system mutes Karaoek part
automatically to prevent the influence to sound effect caused by noise.
3. Fan starting circuit
When power amplifier is with load, for power is large and temperature rise is high, this player
adopts fan to perform heat radiation. When volume is more than 45dB, FAN signal sent out from control
pane N101 changes into high level, V103 9014 and V105 S8050 are on to form power supply loop of fan.
When the connected load is headphone, control line PH-SW is high level, V104 9014 is on to pull down
FAN signal, so no matter how is the volume of system, fan will not start up.
Main element function of decode board is shown as follows:
IC SM8958AC25P (N116): control core of MCU system
IC 493264 (N105): high performance digital audio decoder, including DOLBY decode, DTS
decode and DSP processing
IC CS8415 (N106): serial digital audio signal receiver
IC CS5340 (N108): 2-channel A/D converter
IC CS 4360 (N107): 6-chanel D/A converter
IC 24C02 (N115): state memorizer
IC 74HC04 (N101): 6-channel phase inverter
IC BM1117-3.3 (N109): 3.3V voltage regulating IC, which provides power for CS8415, Cs4923
Working principle: for optical and coaxial signals, after being filtered by inductor, capacitor,
reshaped by phase inverter 74HC04 (N101), they are sent to serial audio digital signal to receive signal
input pin 4, 12 14 of IC Cs8415 (N106), then converse serial digital audio signal to PCM signal through
this IC, and output from pin 16 (sampling speed signal), 17 (main channel clock signal), 18 (audio data
signal) of this IC to pin 25 (sampling speed control signal), pin 26 (clock signal), 22 (PCM data input port
3.2.2 Decode board
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