QSC K.2 Series Service Manual page 14

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.
R98
10.0K
1 PCNT
1/8W
R97
2.00K
1 PCNT
1/10W
C120
100.0PF
5 PCNT
500.0 VDC
SN3
C23
R65 R35
LF_IN
IN
698 10UF 9.09K
1 PCNT 20 PCNT 1 PCNT
1/16W 16V 1/16W
R62
C3
5.62K
1 PCNT 2200PF
10 PCNT
1/16W
50V
A1 A1
C24
R36
LF_SYNC
IN
27PF 21K
5 PCNT 1 PCNT
50V 1/16W
LF_SD
IN
+12VLOW
IN
Figure 4.3.6 - Class D amplifier circuit
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.
Figure 4.3.7 - Top and bottom sides of the AMP/PSU board, showing the locations of the major Class D components
14
R11
1.00K
C7
1 PCNT
100.0PF
1/8W
5 PCNT
+5VA
500.0 VDC
A1
R37 R13
100K 10
1 PCNT 1 PCNT
1/8W 1/16W
LF_+5VA
C25 C27
10UF 0.1UF 1
R8
20 PCNT 10 PCNT
6.3V 16V
2
3.57K
C8 C10
1 PCNT
LF_IN-
1000PF A1 1000PF
1/16W 3
5 PCNT 5 PCNT
C9
50V 50V LF_COMP
4
D2
CCW
1000PF
LF_CSD
5
5 PCNT
TP24 C22 C26
50V
RB751S40T1
VR1
R10
0.1UF 10UF
6
W 2K 10 PCNT 20 PCNT
1.21K
16V 6.3V
1 PCNT
7
LF_-5VA
1/16W
CW
8
R9 R14
R15
698 10
1 PCNT 1 PCNT 5.62K
1/16W 1/16W 1 PCNT
1/16W
A1
-5VA
D10
ES1D
VDD
L5
LF_VDD
C79
1UH
47UF
20 PCNT
100V
A1
D3
BAS21WS-V
R18 R23
5.62K 10K
1 PCNT 1 PCNT
1/16W 1/16W
R55
63.4K
R19
1 PCNT
C33
5.62K 1/10W
1 PCNT 22UF
U1
10 PCNT
Q2
1/16W R54
25V
16 IRFB4227PBF
VAA CSH
C93
2.87
LF_VB
22UF
15
GND VB 1 PCNT
10 PCNT
TP14
1/10W
LF_HO 25V
14
IN- HO
LF_VSW
13
COMP VS
12
CSD VCC
LF_LO
VSS LO 11
Q3
R57
IRFB4227PBF
VREF COM 10
R20
DNI 2.87
R108
9
CSLO DT 1 PCNT
10K 1/10W
10K
98-1073PBF
1 PCNT
1 PCNT
R17 C34
1/16W
1/16W
22UF
0
10 PCNT
NA LD1
25V
R16 NA GREEN
3.57K
1 PCNT
1/16W R113
2.87
1 PCNT
1/10W
R53 D13
2.87 ES1D
1 PCNT
1/10W
L6
LF_VSS
1UH
C81
47UF
VSS 20 PCNT
100V
A1
C35 C42 C57
100.0PF 1.0UF 1.0UF
5 PCNT 10PCT 10PCT
DNI
500.0 VDC 100.0VDC 100.0VDC
C75
0.1UF
A1
10 PCNT R60
D17
200V
C43
10
ES3G
1.0UF 1 PCNT TP15
10 PCNT
L2
1/10W
250V
36UH
DNI 73MW NOM
D18
R93 C36 R58
ES3G
100.0PF
1 63.4K
5 PCNT
1 PCNT 1 PCNT
500.0 VDC
1/10W 1/10W
15MW NOM
R61 R59
10 10K
1 PCNT 1 PCNT
1/10W 1/16W
C37 C58
1.0UF 1.0UF
10PCT 10PCT
100.0VDC 100.0VDC
A1
LF_OUT+
OUT
C5 C45
0.68UF 0.22UF
5 PCNT 5PCT
100V 100.0VDC
C96 R64
0.68UF 10.0K
5 PCNT
1 PCNT
100V
R92 R63
1/8W
49.9 49.9
1 PCT 1 PCT
1.0W 1.0W
A1
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