qsc gx3 sh ts Schematic
8
THIS DOCUMENT CONTAINS PROPRIETARY
INFORMATION WHICH IS THE PROPERTY
OF QSC AUDIO PRODUCTS, THAT MAY NOT
BE DISCLOSED, REPRODUCED OR USED
WITHOUT EXPRESS WRITTEN CONSENT FROM
QSC AUDIO PRODUCTS.
Troubleshoot notes:
1. Power specs:
a. 8 ohm: 300 W = 49 Vrms, Input sen = 1.2 Vrms
b. 4 ohm: 425 W = 41.3 Vrms, Input sen = 1.012 Vrms
2. Output gain: 32.2 dB = 41.3 Vrms
3. Idle current: 0.2A; short limit current: 3.5A /CH, 6.5A /2CH (120V unit)
4. Amplifier would start with an AC voltage above 30 V.
5. Location of Output Transistors: Q13 and Q14 are located on opposite
sides of the heat sink center point, in order to distribute the heat from
each channel more evenly and ensure that the thermal sensor responds
to both channels. Be sure to locate the “out of place” transistor when
D
repairing a bad channel.
6. PCB Revision E: added C62 (Ch2) & C63 (Ch1) = 22uF 25V,
effective date: June 2008
7. Output emitter resistors were upgraded to 3 watts (RE-.02211-00),
effective date: December 2008.
INPUT BOARD
BALANCED INPUT STAGE
(RCA TIP - UNBALANCED)
1.2V NOM INPUT (2V-PK)
GAIN -6DB (2VPK = 1VPK)
J10
3
IN-A-POS
3
2
R
T
S
1
XLR
3
2
1
12
3
1 Vrms, 1k Hz
IN-B-POS
NOTE
CHASSIS
GROUNDS
J3
JACK
1
J9
JACK
FEMALE
2
C
7.50K
1 PCNT
1 PCNT
1/10W
1/10W
C2
0.1UF
5 PCNT
100V
C1
SUB - TOP FILTER, 2-POS
OFF, 100HZ.
CHA = LP, CHB = HP
C5
0.1UF
5 PCNT
100V
IN-B-POS
B
R3
20.0K
1 PCNT
1/8W
IN-B-NEG
R4
20.0K
1 PCNT
1/8W
8
U1
MC33078
C3C1
0.1UF
4
10 PCNT
50V
+14B
-14B
J7
FEMALE
2
J6
JACK
1
3
XLR
NOTE
CHASSIS
GROUNDS
R
T
S
12
3
3
2
1
0.1UF
10 PCNT
50V
MC33078
A
NOTES: UNLESS OTHERWISE SPECIFIED
8
7.50K
1 PCNT
1/10W
0.1UF
5 PCNT
100V
8
U2
4
1 PCNT
1 PCNT
C1
R6
C6
20.0K
R8
20.0K
1/8W
IN-A-NEG
C10
0.1UF
5 PCNT
100V
R9R2R1
39.2K39.2K
1 PCNT
1/10W
R10
24.9K
1 PCNT
1/10W
C1
2
3
U3
MC33078
C13
0.022UF
5 PCNT
50V
2
3
8
4
6
5
5 PCNT
J2A
J2B
C11
220PF
5 PCNT
50V
R18R7
10.0K
1 PCNT
1/10W1/8W
MC33078
2
3
R19
10.0K
1 PCNT
1/10W
C12
220PF
5 PCNT
50V
MC33078
1
U1
C1
7
U3
1
456
7
MC33078
1
U3
R17
2.00K
1 PCNT
1/10W
C7
220PF
50V
R15
10.0K
1 PCNT
1/10W
MC33078
1
U2
R16
10.0K
1 PCNT
1/10W
C8
220PF
5 PCNT
C1C1
50V
MAIN BOARD OPAMP BYPASS CAPS
C18
0.1UF
10 PCNT
11
50V
U6
TRANSCONDUCTANCE OPAMP
6
7
C4
0.1UF
10 PCNT
50V
A-GND-DIS
6
CCW
1
W
VR1
4
J2A
J2A
J2A
J2B
J2B
J2B
6
W
VR2
6
J2A
J2A
J2B
J2B
A1 A1 P3
RET-A
SND-A SND-B RET-B +15V SIG-A CLIP-B
DISPLAY AND GAIN BOARD
C9
0.1UF
10 PCNT
50V
5K5K
CCW
J2A
J2B
LD2
LED RED BIPOLAR
8
J2A
J2B
J2A
J2B
CLIP-A
6
LD3
LED GREEN
C23
0.22UF
10 PCNT
50V
10
9
J2A
J2B
10
C24
0.22UF
10 PCNT
50V
LED GREEN
11
J2A
J2B11J2B
SIG-B
RET-B
J1B
J1A
1
MC33078
20 PCNT
7
C16
22UF
20 PCNT
25V
C20
0.1UF
10 PCNT
50V
C17
22UF
25V
C14
10UF
20 PCNT
35V
C15
10UF
20 PCNT
35V
C1
2
3
C1
4
5
6
7
8
9
10
C1
11
12
C1
8
U5
MC33078
J1A
J1A
J1A
J1A
J1A
J1A
J1A
J1A
J1A
J1A
J1A
4
0.5 Vrms
R20
2.00K
1 PCNT
1/10W
U1
5
6
2
3
SW1
DPDT
8
+14B
C1
-14B
U2
5
6
C19
0.1UF
10 PCNT
50V
MC33078
7
8
U4
MC33078
4
7
+14V
-14V
J1B
J1B
J1B
J1B
J1B
J1B
J1B
J1B
J1B
J1B
J1B
C21
470UF
20 PCNT
16V
C22
470UF
20 PCNT
16V
1
A1
SND-A
2
3
A1
4
+14V
5
6
7
8
P3
9
-14V
Very sensitive
A1
A1
SND-B
12.7K
1 PCNT
1/10W
Test probe can load the bus down
R24
10
11
12
0v when inactive
R26
2.15K
1 PCNT
1/10W
A1
9
R25
TRANSCONDUCTANCE OPAMP
12.7K
1 PCNT
1/10W
U6
7
8
TRANSCONDUCTANCE OPAMP
-13.7v
0.5 Vrms
when gain is
at maximum
1 PCNT
+15V
R21
33.2
1 PCNT
1/8W
R22
5.6
5 PCNT
P3
2W
R23
33.2
1 PCNT
1/8W
8
U7
LM393
4
A1
P3
-15V
6
LED RED BIPOLAR
LD6
R33
3.01K
1 PCNT
LD4
12
J2A
12
1/10W
LOSS-OF-POWER
LD7
SHUTDOWN
LED BLUE
DIODE CLAMPS ON-VOLTAGE
TO THERMAL BUS +0.55V
AC-ON
15v
1 PCNT
D1 D21
IMBD4148
CHANNEL B
R40
1.69K
1 PCNT
1/10W
A1
U4
3
MC33078
C62
22UF
20 PCNT
R41
5.90K
1 PCNT
1/10W
R42
100
1 PCNT
1/10W
A1
C25
0.22UF
10 PCNT
50V
0.22UF
10 PCNT
50V
MC33078
U5
CHANNEL A
R43
1.69K
1 PCNT
1/10W
25V
LIMITER THRESHOLD
P3
1 PCNT
10 PCNT
39.2K
P3
1 PCNT
1/10W
R45
1.69K
1 PCNT
1/10W
A1
C63
R46
1
1.69K
22UF
20 PCNT
1 PCNT
25V
1/10W
R49 R55
39.2K
1 PCNT 1 PCNT
1/10W
1
R48
47.5K
1/10W
C61
0.1UF
50V
3
+5V
1 PCNT
14
15
13
R32
47.5K
1/10W
44mv
0.71v
44mv
5 PCNT
R34
4.75K
1 PCNT
1/10W
R35
100
1 PCNT
1/10W
1
C59
22PF
50V
R27
5.36K
1/10W
A1
2
U6
12
10
16
-14V TH-LIM
+5V
1
5.36K
1 PCNT
A1
1/10W
RET-A
PROTECTION AND LIMITING PARADIGM
CLIP-LIMITING
SINGLE-SIDED, SLOW ATTACK/RELEASE
TRIGGERS ON CLIP AND NEARLY FULL CURRENT
NORMAL CURRENT CLAMPING TRIGGERS CLIP-LIMITING
SOA OVERLOAD
CURRENT TOO HIGH WELL BELOW RAILS
MILD/OCCASIONAL OK - NO EFFECT
SEVERE TRIGGERS CUTBACK TO 25% PK CURR
ON/OFF AND THERMAL MUTING COMMON TO BOTH CHANNELS
THERMAL LIMIT MUTES SEVERAL DEGR ABOVE MAX LIMITING
R36
R30
5.90K
4.75K
1 PCNT
1/10W
1 PCNT
1/10W
3
25
R37
100
4
1 PCNT
1/10W
R31
100
1 PCNT
1/10W
A1
C60
22PF
5 PCNT
50V
R38R28
47.5K
1 PCNT
1/10W
2
3
R29
2.15K
Gain of 8.86
1 PCNT
1/10W
A1
5
3.7V THR SETS ONSET
OF TH LIMITING AT 3.1V,
REACHES FULL LIMIT
AT 2.85V. THEN COLLECTOR
PULLS ABOVE GND AND
TRIGGERS MUTE.
P3
6v
D2
R50
IMBD4148
221K
1/10W
C28
10UF
20 PCNT
35V
P3
R57
243K
1 PCNT
1/8W
C31
22PF
5 PCNT
200V
6
MC33078
5
7
U4
C27
10PF
5 PCNT
FB-B
200V
R54
16.5K
FEEDBACK
1 PCNT
8V PK INPUT
1/2W
= 80V PEAK OUT
47.5K
1/10W
MMST3906
Q2
2 3
R51
10M
1 PCNT
1/8W
R52C26
10M
1 PCNT
1/8W
Q1
MMST3906
R53R47
47.5K
1 PCNT
1/10W
C30
22PF
5 PCNT
200V
6
MC33078
5
7
U5
C29
10PF
5 PCNT
FB-A
200V
R56
16.5K
FEEDBACK
1 PCNT
1/2W
4.88 Vrms
when gain is
at maximum
5
3.73v
R60 R64
3.01K
1 PCNT
1/10W
1
TH-LIM
2 3
5.7v
3.3V THRESH
TRIGGERS MUTE
AT TH BUS = 2.75V
+15V
+CUT-B
AMPLIFIER
GAIN BLOCK
R61
47.5
1 PCNT
1/10W
C32
0.0015UF
5 PCNT
200V
20 PCNT
-CUT-B
R63
243K
1 PCNT
1/8W
R58
243K
1 PCNT
1/8W
+CUT-A
C36
10UF
20 PCNT
AMPLIFIER
GAIN BLOCK
CLIP-A
R62
47.5
1 PCNT
1/10W
C33
0.0015UF
5 PCNT
200V
8V PK INPUT
= 80V PEAK OUT
C37
10UF
20 PCNT
-CUT-A
R59
243K
1 PCNT
1/8W
THERMAL TRACKING
931
1 PCNT
1/10W
+15V
MMST3906
Q3
-14.6v
R69
P3
39.2K
1 PCNT
1/10W
+14V
1
R65
47.5K
1 PCNT
1/10W
C34
10UF
20 PCNT
35V
P3
CLIP-B
BIAS
DIODES
P3
C35
10UF
35V
R66
47.5K
1 PCNT
1/10W
-15V
14.8v
+15V
12.4v
1
R67
47.5K
1 PCNT
1/10W
14.34v
1.76v
2.96v
35V
P3
+0.57v
BIAS
DIODES
-0.57v
P3
35V
-2.94v
R68
-13.7v
47.5K
-1v
1 PCNT
1/10W
1
-14.24v
-1.6v
-15V
-14.8v
-12.1v
VOLTAGE REGULATOR
8 1
367
R78
14.3K
1 PCNT
1/10W
3.2v
6v
2
Q4
MMST3904
3
R70
2.15K
1 PCNT
1/10W
R71
475
1 PCNT
1/10W
D3
MURS160T3
D4
MURS160T3
R72
475
1 PCNT
1/10W
R73
2.15K
1 PCNT
1/10W
MMST3906
Q51
2 3
-14V
2
+14V
Q6
MMST3904
13.8v
3
R74
1v
2.15K
1 PCNT
1/10W
R75
475
1 PCNT
1/10W
D5
MURS160T3
D6
MURS160T3
R76
475
1 PCNT
1/10W
R77
2.15K
1 PCNT
1/10W
3
MMST3906
Q7
2
-14V
VOUTVIN
P3
+5V
HYST F/B
3
2
NL: 40 mV-
Ù
8 : 230 mV-
Ù
4 : 300 mV-
NL: -40 mV8 : -230 mV-
Ù
4 : -300 mV-
Ù
+5V
1 PCNT
1
P1
1
P2
1
C38
0.1UF
10 PCNT
50V
R79
100K
1/10W
1
60 mV idle
60 mV idle
4
SENSOR
0C - 1.8V
25C - 1.58V
55C - 1.2V
65C - 1.07V
95C - 0.75V
U9U8
1 2
V+
C39
0.1UF
10 PCNT
50V
+15V
R88
10.0K
1 PCNT
1/10W
LM393
1
Run: 106 mV
RUN, LO
U7
MUTE, 1.2V
R80
33.2
1 PCNT
1/8W
1
2
Q8
2SC4793
3
R81
10
1 PCNT
R82
10
1 PCNT101 PCNT
1/8W
2SA1837
Q9
2 3
R83
33.2
1 PCNT
1/8W
R84
33.2
1 PCNT
1/8W
60 mV idle
2
Q10
2SC4793
3
R85
10 10
1 PCNT
1/8W
R86
10
1 PCNT
1/8W
3
2SA1837
Q11
2
1
R87
33.2
1 PCNT
1/8W
4
1.58v
VO
GND
SENSOR
C40
0.1UF
10 PCNT
50V
R97
2.21K
1 PCNT
1/10W
R11
10.0K
1 PCNT
1/10W
R5
1
10.0K
1 PCNT
1/10W
P3 P3
R89 R98
0.15
5 PCNT
2W
1
Q12
2SA1962
2 3
R90
10
1 PCNT
1/8W1/8W
R91
1/8W
2
1
Q13
2SC5242 2SC5242
3
R94 R99
0.15
5 PCNT
2W
R95 R100
0.15
5 PCNT
2W
Ù
Ù
8 : 195 mV~
4 : 400 mV~
1
Q14
2SA1962 2SA1962
2 3
R92
1 PCNT
1/8W
R93
10
1 PCNT
1/8W
2
Q15
2SC5242 2SC5242
3
R96 R101
0.15
5 PCNT
2W
Ù
Ù
8 : 195 mV~
4 : 400 mV~
C45
P3
0.22UF
10 PCNT
50V
LM393
5
6
THERMAL GAIN SET AT 3.66
FOR 4.4V AT 55C, FAN SPEED
3
3 3
1
0.15
5 PCNT
2W
Q16
2SA1962
2 3
7
U7
C46
0.22UF
P3
10 PCNT
50V
R102
5.90K
1 PCNT
1/10W
Mute: 0.7v
Run: 14.8v
+CUT-B
Q17
MMST3904
Run: 106 mV
MMST3906
Q18
-CUT-B -CUT-A
Mute: 0.6v
Run: -14.2v
+VCC B 88V
D7
1N5399
P1
PEAK CLAMP
C41
NA
NA
NA
C42
NA
NA
NA
1
Ù
8 : 170 mV-
1
1
R140
475
1 PCNT
1/10W
1
R103
100
1 PCNT
1/10W
P1
2
Q19
3
0.15
5 PCNT
2W
-VCC B -88V
0.15
5 PCNT
2W
Ù
4 : 320 mV-
Q20
2 3
2
Q22
MMST3904
3
3
MMST3906
Q23
2
D8
1N5399
+VCC A 88V
D9
1N5399
P2
PEAK CLAMP
R104
1 PCNT
1/10W
2
3
Ù
Ù
8 : 170 mV-
4 : 320 mV-
R141
1 PCNT
1/10W
100
P2
Q21
0.15
5 PCNT
2W
-90 V @ NL
-79 V @ 8
-72 V @ 4
-71 V @ 2.66
-86 V @ Short
1
475
1
D10
1N5399
-VCC A -88V
Ù
Ù
Ù
C43
NA
NA
NA
C44
NA
NA
NA
1
3
+5V
R110
383
1 PCNT
1/10W
4.88v
MMST3906
1
Q31
-15.2v
2 3
SOA SENSE
1
1
2 3
+90 V @ NL
+79 V @ 8
+72 V @ 4
+71 V @ 2.66
+86 V @ Short
SOA SENSE
1
3
50 mV-
50 mV-
2 3
FB1 FB2
SI1 BB1
SI Target
EMITTER R
0C - NIL
25C - NIL
55C - START
65C - 2MA
95C - 7MA, 1.4V
R120
1 PCNT
D19
1N4743A
13v
12.75v
zener
1
+3.1v
R115
100K
1 PCNT
18.8v
1/10W
FAN SPEED
CIRCUIT
R112 R126
1.13K
1 PCNT
1/10W
D15
IMBD4148
D16
IMBD4148
Ù
Ù
1
1
Ù
D17
IMBD4148
D18
IMBD4148
R111
1.13K
1 PCNT
1/10W
R113
56.2K
1 PCNT
1/8W
R114
1.13K
1 PCNT
1/10W
Badboard Mark
R116
1.13K
1 PCNT
1/10W
1
R117
56.2K
1 PCNT
1/8W
P2
P1
634
1/10W
4.23v
D20
IMBD4148
3.72v
3
MMST3906
Q33
R121
10.0K
1 PCNT
0.514v
1/10W
B-LO
W8
W6B
W6A
R118 R122
0.1
5 PCNT
2W
P1
R124
2.00K
1 PCNT
1/10W
Q34
MMST3904
W4
SPKR(BLACK)
W2B
14.0 IN
18 AWG
W2A
P2
R119 R123
0.1
5 PCNT
2W
R125
2.00K
1 PCNT
1/10W
Q35
MMST3904
FP1 FP2
1
1
1
1
1
1
+15V
R105
4.75K
1 PCNT
1/10W
TH-BUS
5.72v
TH BUS
0C - 6.6V
25C - 5.8V
55C - 4.4V
65C - 3.9V
85C - 3.17V
95C - 2.75V
Mute: 0.7v
Run: 14.8v
+CUT-A
2
1
Q26
MMST3904
3
MMST3906
1
Q27
Mute: 0.6v
Run: -14.2v
R106
69.8K
1 PCNT
1/8W
2
Q28
MMST3904
3
D11
MURS160T3
D12
MURS160T3
Q30
MMST3906
P1
R107
69.8K
1 PCNT
1/8W
R108
69.8K
1 PCNT
1/8W
Excessive negative output current
cuts positive biasing side
2
Q29
MMST3904
14.34v
1.76v
2
+0.51v
Q24
MMST3904
D13
MMST3906
Q25
-14.24v
MURS160T3
D14
MURS160T3
0.517v 0.517v
-0.51v
MMST3906
Q32
Excessive positive output current
cuts negative biasing side
R109
69.8K
1 PCNT
1/8W
BT1 BT2
1
3
3
2
-1.6v
P2
AI1
AI Target1Board Target1Board Target1Board Fiducial1Board Fiducial1Panel Fiducial1Panel Fiducial
OF1 OF2
Offset Target1Offset Target
3
+15V
15.74v
J5
1
FAN
J5
2
11.44v idle
0.534v
4.3v idle
2
1
Q36
TIP31C
3
-15.8v
-15V
4.6 IN
18 AWG
11.0 IN
18 AWG
11.0 IN
18 AWG
10
5 PCNT
2W
R127
10
5 PCNT
2W
J13
FEMALE
2- 2+
JACK
1+1-
10 PCNT
C48
0.1UF
250V
21
43
B-HI
W7
W5B
4.6 IN
18 AWG
1
1
11.0 IN
18 AWG
W5A
1
11.0 IN
18 AWG
SPKR-B
IMON-B
0.1
5 PCNT
2W
SIG-B
2
Q37
MMST3904
2
3
1
3
P1
4.6 IN
18 AWG
J12
FEMALE
2- 2+
B-LO
14.0 IN
18 AWG
SPKR(BLACK)
R128
10
5 PCNT
2W
R129 R133
10
5 PCNT
2W
IMON-A
0.1
5 PCNT
SIG-A
2W
2
Q38
MMST3904
2
3
1
3
P2
1+1-
JACK
0.1UF
10 PCNT
B-HI
SPKR+
(WHITE)
C47
250V
1
1
P1
21
43
W1B
W1A
P2
1 2
R131
15.4K
1 PCNT
1/8W
4.6 IN
18 AWG
W3
1
SPKR+
(GRAY)
1
14.0 IN
18 AWG
14.0 IN
18 AWG
41.3 Vrms
1
SPKR-A
1 2
R130
15.4K
1 PCNT
1/8W
CONTRACT NO.
DRAWN
IAN OVERHOLT
1
CHECKED
ISSUED
DENISE DELARM
SEED FILE NO.
SH_200001.SCH NONE
REV CHK APPROVED/DATEEFF. DATEDESCRIPTION
A DDRAB03/12/08PRODUCTION RELEASE ECO 8578 ADD C62,63
R113, R117 56.2K DELAY SOA CUTBACK
-15V
REVISIONS
+15V
C54 C55
1000UF
20 PCNT
P3
35V
IMBD4148
35V
3
BR1
BRIDGE RECTIFIER
AC1
2
1
-
+
AC2
4
D22
IMBD4148
3.01K
1 PCNT
1/10W
3K MUTES
IN 30MS
3
BR2
BRIDGE RECTIFIER
AC1
2
1
-
+
AC2
4
1
2
3
SG1
3
BR3
BRIDGE RECTIFIER
AC1
2
1
-
+
AC2
4
SCHEMATIC DIAGRAM
CAGE CODE
00PW4
D
SCALE SHEET 1 OF
R132
10
5 PCNT
2W
L1
2UH
10
5 PCNT
2W
L2
2UH
APPROVALS
C49
4700UF
20 PCNT
100V
FB-B
C50
4700UF
20 PCNT
100V
C51
4700UF
20 PCNT
100V
FB-A
C52
4700UF
20 PCNT
100V
R142
1K
5 PCNT
1/4W
P3
AC-ON
DATE
05/15/2007
03/11/2008DAVID GALVAN
03/12/2008
PLOT DATE:
1000UF
20 PCNT
C53 R134
10UF
20 PCNT
35V
P3
MAIN SEC B, 115VAC
WITH RECTIFIER, FUSE
AND EMI SNUBBER
MAIN SEC A, 115VAC
WITH RECTIFIER, FUSE
AND EMI SNUBBER
2
12
E1
F1
1
XF-12V (YELLOW)
24V
C56
5A
0.1UF
10 PCNT
50V
R135
10
1 PCNT
1/8W
E2
1
XF-CT (GRAY)
P3
E3
F2
1
XF-12V (YELLOW)
24V
5A
AUX COIL, 24V CT
E4
1
F3
32V
10A
F4
32V
10A
XF-65V CH2 (RED)
E5
1
XF-65V CH2 (GREEN)
E7
1
XF-65V CH1 (VIOLET)
E8
1
XF-65V CH1 (BLUE)
C57
0.1UF
10 PCNT
200V
R136
10
1 PCNT
1/8W
E6
1
P1 P2P3
C58
0.1UF
10 PCNT
200V
R137
10
1 PCNT
1/8W
AUDIO PRODUCTS, LLC.
COSTA MESA, CALIFORNIA
GX3 AMPLIFIER
SH-200001-00
CAD FILE NO.
AR-200001-00-D.ZIP
1
REVDWG NO.SIZE
A
D
C
B
A
1
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