Casio CTK-750 Service Manual page 14

Power Amplifier (LA4620)
The power amplifier is a two-channel balanced amplifier with standby switch. The following figure shows
the internal diagram of the amplifier.
Internal Diagram of LA4620
3
IN11+
IN11- 5
4
IN12-
6
PriGND
IN21+ 9
IN21- 7
8
IN22-
Power Supply Circuit
The power supply circuit generates six voltages as shown in the following table. VDD voltage is always
generated. The others are controlled by APO signal from the CPU.
Name Voltage
VDD +5.1V
DVDD +5.3V
AVDD +5.2V
LVDD +5.2V
VCC +12V
VD +12V
+
Input
Pre-drive
Amp.
Amp.
-
-
Input
Pre-drive
Amp.
Amp.
+
Terminal
Protection
Circuit
+
Input
Pre-drive
Amp.
Amp.
-
-
Input
Pre-drive
Amp.
Amp.
+
16
2
NC DC MUTE
CPU, Reset IC, Gate array, Working strage RAM
DSP, Key touch LSI, Sound source ROM, Effect RAM, DAC
DAC, Filter
LED driver
Pilot lamp
Power amplifier
— 12 —
Power
Amp.
RL Short
Protector
Power
Amp.
Pop Noise
Ripple
Prevention
Filter
Circuit
Power
Amp.
RL Short
Protector
Power
Amp.
10 11 13
VCC2 ADJ
For operation of
Boot11
19
OUT11
20
21 PoGND1
22 OUT12
23 Boot21
1
VCC1
18 Boot21
OUT21
17
PoGND2
15
OUT22
14
12 Boot22