14
QSC, LLC
Class D amplifier
There are two class D half-bridge amplifiers in the module. One amplifier is designed for low frequency while the other is
designed for high frequency. The power MOSFETs in the LF and HF sections are different devices, so pay close attention
when replacing them. Each of the amplifiers are a type of class D amplifier called ‘self-oscillating’, as opposed to a class D
amplifier that requires a clock to switch. To avoid interference, the amplifiers oscillate at different frequencies. The LF
amplifier oscillates at 372 kHz and the HF amplifier oscillates at 412 kHz. The class D driver used in this design has a
built-in PWM modulator, which allows the driver to accept an inverted analog input (as opposed to a PWM input) directly.
The modulated switching voltage must be filtered to recover the audio signal before being connected to a transducer. The
filter uses a toroid inductor and film capacitor for each channel. In the LF and HF amplifiers, different pairs of inductance/
capacitance are utilized since the output frequency and power is drastically different between the two channels. Although
not required with the type of self-oscillating amplifier used in the amplifier module, small Zobel filters are present on each
channel to aid in stability and help reduce cross-channel interference during over-current (OC) conditions.
A 6-pin molex connector, sticking through the back of the module into the loudspeaker cabinet, brings both amplifier
outputs to the transducers via a detachable wire harness. Another pair of wires goes to the front LED which is mounted in
the loudspeaker cabinet.
DNI
73MW NOM
15MW NOM
DNI
DNI
100.0VDC
1.0UF
10PCT
100.0VDC
1.0UF
10PCT
100.0VDC
1.0UF
10PCT
100.0VDC
1.0UF
10PCT
1.0W
IRFB4227PBF
1/10W
10
1 PCNT
20 PCNT
47UF
100V
1UH
47UF
1UH
20 PCNT
100V
50V
5 PCNT
10
1.21K
1 PCNT
1/16W
1/16W 1 PCNT
5.62K
RB751S40T1
1/16W
1/16W
1 PCNT
698
5 PCNT
500.0 VDC
2K
9.09K
20 PCNT
1/16W
1/16W
98-1073PBF
NA
0
NA
10 PCNT
1 PCNT
50V
5 PCNT
1000PF
50V
5 PCNT
6.3V
1 PCNT
5.62K
2200PF
50V
10 PCNT
1/16W
1 PCNT
698
27PF
1 PCNT
21K
1/16W
10UF
16V 1/16W
1 PCNT
100.0PF
1/10W
1 PCNT
2.00K
3.57K
1 PCNT
1/16W
1 PCNT
1/8W
100K
10.0K
1 PCNT
1/8W
5 PCNT
50V
1000PF 1000PF
5 PCNT
100.0PF
500.0 VDC
1.00K
1 PCNT
1/8W
2.87
1/10W
1 PCNT
ES1D
ES1D
2.87
1 PCNT
1/10W
16V
0.1UF
10 PCNT 20 PCNT
10UF
3.57K
1 PCNT
20 PCNT
10UF
6.3V
1 PCNT
1/16W
10
16V
0.1UF
10 PCNT
10K
1 PCNT
1/16W
25V
22UF
5.62K
1/16W
1 PCNT
5.62K
1 PCNT
1/16W
10 PCNT
25V
22UF
1/16W
10K
1 PCNT
BAS21WS-V
GREEN
1/16W
10K
1 PCNT
1 PCNT
2.87
1/10W
2.87
1 PCNT
1/10W
1/10W
63.4K
1 PCNT
1
1 PCNT
1/10W
100.0PF
5 PCNT
500.0 VDC
36UH
250V
10 PCNT
1.0UF
200V
10 PCNT
0.1UF
1 PCNT
1/10W
10
ES3G
1/16W
10K
1 PCNT
1/10W
63.4K
1 PCNT
100V
0.68UF
5 PCNT
ES3G
5 PCNT
100V
0.68UF
1.0W
49.9
1 PCT
100.0VDC
0.22UF
5PCT
49.9
1 PCT
1/8W
1 PCNT
10.0K
100.0PF
500.0 VDC
5 PCNT
IRFB4227PBF
25V
10 PCNT
22UF
TP24
TP14 TP15
SN3
R97
C120
R98
R59
R58
C96
R108
R92
L5
C79
L6
C81
R93
C75
D10
D2
C25
R13
R20
R17
R16
C22
R15
R11
C7
R8
R10
R9
D3
R19
R18 R23
C10C8
VR1
C9
C27
R14
C26
U1
C23
C5
R62
C3
R65
C93
C33
C24
R36
R35
R37
R55
C43
C58
C57
R113
LD1
R64
C45
R63
D17
C42
D18
L2
C35
R60
Q2
R61
C36
Q3
R54
D13
R57
C37
R53
C34
LF_VSS
LF_VDD
LF_COMP
+12VLOW
LF_SD
LF_SYNC
LF_IN
LF_OUT+
LF_VB
LF_HO
LF_LO
LF_CSD
LF_IN-
LF_-5VA
LF_+5VA
LF_VSW
6
13
7
12
15
1
11
3 14
2
98
16
5
4
10
OUT
IN
+5VA
A1
A1
VSS
-5VA
A1
A1
CW
W
CCW
A1
CSH
VB
HO
VS
VCC
LO
COM
DTCSLO
VREF
VSS
CSD
COMP
IN-
GND
VAA
A1
A1
A1
A1 A1
IN
IN
IN
Figure 4.3.6 - Class D amplifier circuit
Figure 4.3.7 - Top and bottom sides of the AMP/PSU board, showing the locations of the major Class D components
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