Alto A400.4 Service Manual
MODEL: A400.4
www.altoproaudio.com
Version 1.0
CONTENT
1. Introduction.............................................................................................1
2. Specification............................................................................................2
3. Block Diagram.........................................................................................3
4. Schematic Diagram.................................................................................4
5. Wiring Diagram......................................................................................10
6. Printed Circuit Board..........................................................................11
7. Exploded View & Mechanical Parts List..................................................13
8. Electrical Parts List.............................................................................15
1. Introduction
˙ 1.5U 1/2 rack, multi-channel high power amplifier.
˙ Fantastic audio quality even with extremely high volume levels.
˙ Solid and durable, can be mounted into a cabinet.
˙ User-controllable clip limiter.
˙ 4×120Watts on 4 ohms (EIAJ)
˙ Balanced XLR inputs and 1/4” TRS jack to ensure noiseless long wiring.
˙ 1/4”TS jack for sp-output.
˙ Front panel LED indicators for signal, limit and clip.
˙ Accurate gain control
˙ Independent thermal overload protection on each channel automatically
protects amplifier and speakers.
˙ Single channel over-heat protection.
- 1 -
2. Specification
MODEL
20Hz 20KHz@0.1%THD, Stereo Mode
8 ohms per channel(EIAJ)
4 ohms per channel(EIAJ)
4 ohms per channel(RMS)
Input Sensitivity @4 ohms
Controls
Indicators (per channel)
Connectors of each channel
A400.4 DRAGONFLY
65W
120W
62W+3W
+3dBu
FRONT: Power switch, LEVEL knobs
REAR: Four LIMITER Switches for channel 1- channel 4
Power-On: Green LED
Clip: Red LED
Limit: Yellow LED
Signal: Green LED
Input: COMBO connector
Output: 1/4" TS jack connector
(at THD:1%)
Power Supply
Dimension
Net Weight
190-240 Vac~50Hz / 95-120Vac~60Hz
314mm x 208.5mm x 66.6mm
3.8Kg
- 2 -
3. Block Diagram
D
4
C
B
A
PM8PWR
POWER SUPPLY
321
A400.4
AMP
D100W
AMP
D100W
BLOCK DIAGRAM
PRE-AMP
1 2 34
CH1
D
C
CH2
- 3 -
CH3
B
CH4
A
4. Schematic Diagram
D
C
B
A
PJ4
3c
4
1
2
3
CN7
CON3
C6
100P
100P
1
C5
1
2
3
4
CN10
2
3
CON4
4
5
6
1
2
3
CN8
CON3
C8
100P
C7
100P
4d
1
2
CN17
CH4_S P+
SW2A
4
1
2
3
4
5
X1
X2
X3
321
CN3
6
SW2B
CN-BAL-COMBI
SW PS-22E85L
SW4B
5
6
P
1
SW PS-22E85L
SW4A
CH3
P
SW PS-22E85L
2
3
1
2
3
4
5
X1
X2
X3
SW PS-22E85L
CN4
6
PJ3
3c
4d
CN-BAL-COMBI
1
2
CH4
CN15
2b
CON2
2b
CON2
PHONEJACK5 (5-PIN)
5e
1a
C12
100P
1
2
CN18
CON2
CH4_S P-
PHONEJACK5 (5-PIN)
5e
1a
C11
100P
1
2
CN16
CON2
CH3_S P+
1
2
3
CN5
1
X1
X2
X3
CON3
C2
100P
6
100P
1
SW1A
4
SW1B
C1
2
3
4
5
1
2
3
4
CN9
2
3
SW PS-22E85L
5
6
P
SW PS-22E85L
CON4
4
5
6
SW3B
1
SW3A
P
SW PS-22E85L
2
3
X1
X3
SW PS-22E85L
1
2
3
CN6
1
X2
CON3
C4
100P
C3
100P
2
3
4
5
6
PJ2
3c
4d
2b
1
2
CN13
CON2
CH2_S P+
CN1
CN-BAL-COMBI
CH1
CN2
CN-BAL-COMBI
CH2
PJ1
3c
4d
2b
1
2
CN11
CON2
CH3_S P-
PHONEJACK5 (5-PIN)
5e
1a
C10
100P
1
2
CN14
CON2
TP1
TP-2
CH2_S P-
PHONEJACK5 (5-PIN)
5e
1a
C9
100P
1
2
CN12
CON2
1 2 34
CH1_S P+
D
C
B
CH1_S P-
A
- 4 -
A
GND
R51
CN7
82R
123
B
CLIP
SIG
LIMI TER
12345
GND
CN13
4
CON4
R47
270R
CON5
R54
30R
82R
R50
180R
R53
LIMI TER
C
CLIP
12345
CON5
R24
30R
82R
R20
180R
R23
CN11
GND
CLIP
SIG
LIMI TER
12345
CON5
R52
30R
R49
270R
180R
R45
D
8
CLIP
SIG
LIMI TER
12345
CN5
7654321
R15
270R
CON5
R21
82R
GND
R22
30R
R19
180R
123
4
CN3
SIG
CN8
CON4
R17
270R
1
U5A
NJM4580L
C13
R26
82K
56pF/50 cer
123
CH1-OUT
CN4
C11
R6
56pF/50 cer
C9
47uF/25V
1
C6
100pF/50 cer
R4
10K
3
2
R1
15K
R2
C1
22uF/50V
CN1
CON3
GND
CH1 GAIN
15K
123
CH2-OUT
U2
17K4
R5
U1A
C2
CON3
2
R25
41
VTL
1
2
10K
VR1
NJM4580L
R3
10K
C5
22uF/50V
CH1-IN
3
R27
10K
10K
GND
2 3
U3A
NJM4580L
3
R9
10K
GND
A10K
C7
100pF/50 cer
GND
GND
100pF/50 cer
GND
GND
C14
56pF/50 cer
C12
56pF/50 cer
C10
47uF/25V
1
R8
10K
2
R7
15K
R10
C3
22uF/50V
CN2
7
82K
6
R28
41
VTL
7
5
6
VR2
10K
C8
100pF/50 cer
22uF/50V
CH2-IN
5
10K
A10K
GND
GND
GND
U5B
NJM4580L
R30
10K
GND
2 3
U3B
NJM4580L
R13
10K
GND
GND
C28
100pF/50 cer
C31
56pF/50 cer
123
CH3-OUT
CN12
C30
56pF/50 cer
C29
47uF/25V
7
R34
10K
6
R31
15K
R32
C23
22uF/50V
CN9
R29
U4
R14
17K4
10K
R12
CH2 GAIN
U6A
NJM4580L
R11
3
15K
C4
123
CON3
1
82K
2
R55
41
VTL
1
3
2
VR3
3
10K
A10K
R57
U8A
R39
U10A
10K
GND
2 3
NJM4580L
10K
GND
R56
CON3
CH4-OUT
GND
U7
R36
17K4
10K
R35
CH3 GAIN
U1B
5
15K
C24
123
CON3
R33
NJM4580L
10K
C27
22uF/50V
CH3-IN
100pF/50 cer
GND
GND
GND
C33
100pF/50 cer
NJM4580L
GND
C35
56pF/50 cer
C34
56pF/50 cer
C44
47uF/25V
7
R38
10K
6
R37
15K
R40
C25
22uF/50V
CN10
7
82K
6
R58
41
VTL
7
6
10K
VR4
NJM4580L
10K
C32
22uF/50V
CH4-IN
U10B
NJM4580L
5
R60
10K
GND
10K
2 3
U8B
NJM4580L
5
R43
10K
GND
GND
CN6
15V
84
84
123
CON3
-15V
GND
C42
220u/25V
C43
220u/25V
U10C
NJM4580L
C40
104P
C41
104P
U8C
NJM4580L
C38
104P
C39
104P
A10K
84
U6C
NJM4580L
C36
104P
C37
104P
GND
GND
84
U5C
NJM4580L
C19
104P
C20
104P
100pF/50 cer
GND
84
U3C
NJM4580L
C17
104P
C18
104P
R59
U9
R44
17K4
R42
CH4 GAIN
U6B
R41
5
15K
C26
123
CON3
84
U1C
NJM4580L
C15
104P
C16
104P
D
C
B
A
1 2 3 4 5 6 78
- 5 -
D
4
321
C
B
A
CN1
LED3
GR
LED2
YEL
3
4
5
LED1
1
2
RED
CON5
CN2
LED6
GR
LED5
YEL
4
5
LED4
RED
1
2
3
CON5
1 2 34
D
C
B
A
- 6 -
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