JBL Consumer Products Inc.
250 Crossways Park Drive
Woodbury, N.Y. 11797
A Harman International Company
Rev B 7/2003
SUB125/125a
Amplifier/Subwoofer
SERVICE MANUAL
2
Amplifier/Subwoofer SUB125
GENERAL SPECIFICATIONS
SCS125/125a System
Frequency Response
35Hz – 20kHz (–6dB)
SUB125
Amplifier . . 75 watts RMS
Bass .....8"woofer, bass-reflex enclosure
Dimensions (HxWxD)
14-1/8 x 13 x 13 inches
359 x 330 x 330mm
Weight . . . 27.5 lbs/12.5 kg
Refinements may be made on occasion to existing products without notice,
but will always meet or exceed original specifications unless otherwise stated.
TABLE OF CONTENTS
COVER...........................................................................1
GENERAL SPECIFICATIONS .......................................2
TABLE OF CONTENTS .................................................2
SCS125/125a SPECIFICATIONS..................................3
CONTROLS AND THEIR FUNCTION...........................5
SCS125/125a SPEAKER LEVEL CONNECTIONS ......6
SCS125/125a LINE LEVEL CONNECTIONS ...............7
SUB125 TEST SET UP AND PROCEDURE................8
SIMPLE TROUBLESHOOTING.....................................9
Service Bulletin JBL9901 ..........................................10
SCS125/125a PACKING..............................................11
SUB125 EXPLODED VIEW .........................................12
SUB125 PCB COMPONENT SIDE .............................13
SUB125 PCB SOLDER SIDE......................................14
SUB125 ELECTRICAL PARTS LIST ..........................15
SUB125 INTEGRATED CIRCUIT DIAGRAMS ...........17
SUB125 POWER AMP SCHEMATIC DIAGRAM........18
SUB125 PRE-AMP SCHEMATIC DIAGRAM ..............19
The SUB125 is part of the SCS125/125a system
SCS125/125a SPECIFICATIONS
LINE VOLTAGE Yes/No
Hi/Lo Line Unit Notes
US 120vac/60Hz Yes 108-132 Vrms Normal Operation
EU 230vac/50-60Hz Yes 207-264 Vrms Normal operation, MOMS
required
Asia 100vac/50Hz Yes 90-110 Vrms Normal Operation
Spec. Unit Limits Conditions Notes
Amp Section
Type (Class AB, D, other) AB AB n/a Sink required for Class AB
Load Impedance (speaker) 4 Ohms n/a Nominal Z-curve required
Rated Output Power 80 Watts 80 1 input driven
THD@ Rated Power 0.08 % 0.3 22k filter
THD @ 1 Watt 0.1 % 0.5 22k filter
DC Offset 10 mV-DC 20 @ Speaker Outputs
Damping factor <200 DF n/a
Input Sensitivity
Input Frequency 50 Hz 50 Nominal Freq. 1 input driven
Line Input 220 mVrms ±2dB To Rated Power 1 input driven
Speaker/Hi Level Input 4.26 Vrms ±2dB To Rated Power (-26dB below Line In)...1
input driven
Signal to Noise
SNR-A-Weighted 100 dBA 90 rel. to rated power A-Weighting filter
SNR-unweighted 80 dBr 60 rel. to rated power 22k filter
SNR @ 1W-unweighted 60 dBr 55 rel. to 1W Output 22k filter
Residual Noise Floor 1.5 mVrms 2.5 Volume @max, using RMS reading DMM/VOM (or A/P)
Residual Noise Floor 1 mVrms(max) 2 Volume @max, w/ A/P Swept Bandpass Measurement
(Line freq.+ harmonics)
Input Impedance
Line Input 15K ohms n/a Nominal
Speaker/Hi Level Input 4.7K ohms n/a Nominal
Filters
Low Pass (fixed or
variable)
fixed — —
Low Pass filter (point or
range)
135 Hz ±2dB -3dB Point
Slope 24 dB/Octave n/a
Q 1.8 Damping n/a 2 cascaded 2nd order
filters of 1.8 &0.7 Q
Subsonic filter (HPF) 31 Hz ±2dB -3dB Point
Slope 12 dB/Octave n/a
Q 1.4 Damping n/a
3
Amplifier/Subwoofer SUB125
Signal Sensing (ATO)
Auto-Turn-On (yes/no) yes — functional
ATO Input Frequency 50 Hz functional
ATO Level 2 mV functional 2mV@50Hz into Line Input
w/ 1 ch. driven
ATO Bandwidth 5k Hz functional ATO-LPF for noise
immunity
DV1 measured 7mV @
5kHz…. 2mV @ 1kHz
ATO Turn-on time 5 ms functional Amp connected and AC on, then input signal applied
Auto Mute/ Turn-OFF Time 20 minutes functional T before muting, after
signal is removed
Power on Delay time
3 sec. functional AC Power Applied
Transients/Pops
ATO Transient 5 mV-peak 10 @ Speaker Outputs
Turn-on Transient 50 mV-peak 100 @ Speaker Outputs AC Line cycled from OFF to
ON
Turn-off Transient 50 mV-peak 100 @ Speaker Outputs AC Line cycled from ON to
OFF
Efficiency
Stand-by Input Power 10 Watts n/a @ nom. line voltage
Power Cons.@rated power 160 Watts n/a @ nom. line voltage
Protection
Short Circuit Protection Yes — functional Direct short at output
Thermal Protection 65 deg.
C
— functional @1/8 max unclipped
Power
DV1:Plate=50deg.C
max.Tab=90deg.C max.T-on
=65deg.C
DC Offset Protection yes — functional DC present at Speaker
Out leads
Relay or crowbar (for
driver/fire protection)
Line Fuse Rating 2 Amps 2 Type-T or Slo Blo External fuse with UL/SEMKO
rated holder
4
Amplifier/Subwoofer SUB125
1. Speaker Level Outputs - Connect the Left, Center
and Right speakers to these connectors.
2. Speaker Level Inputs - These High Level Inputs are
for receivers that do not have line-level “pre-amp out”
or “subwoofer out” jacks. When a pair of main or
satellite speakers are attached to the OUTPUT
terminals, they are driven the full range of frequencies
as generated by the music source (receiver, amplifier,
etc.)
3. Line Level Input - These left and right Line Level
Inputs are normally used when the receiver/ processor
has line-level “pre-amp out ” or “subwoofer out” jacks.
4. Auto/On Switch - This switch allows you to set the
Mode of the Amplifier. Turn the switch to Auto to
cause it to Auto-matically turn on when it receives a
signal and Auto-matically turn off after twenty minutes
without a signal. If this switch is left “On”, the
subwoofer will always be ON when the power switch
is turned On, regardless of input signal.
5. Subwoofer Level - This knob controls the volume
level of the SUB125.
6. LED - Red & Green. The LEDs indicate the Mode
status that the subwoofer is in. When the SUB125 is
turned OFF neither LED will be lit. The Green LED
will light when the SUB125 is ON and receiving a
signal. The Red LED will light when the amplifier has
not received a signal for twenty minutes. The
subwoofer will turn on when your receiver/amplifier
begins playing again.
7. Power Switch - This the master power switch. Use it
(in Off mode) to disconnect power to the amplifier.
8. Fuse - Use only same type of fuses. For the U.S.
120V version use only a 2A 250V fuse. For the
European 230V version use only a 1A fuse.
9. AC Cord
5
Amplifier/Subwoofer SUB125
AC 120V ,60Hz
160W
~
POWER
R
L
MIN
MAX
FUSE
STAND BY ON
FUSE
2A/250V
SUB125
LINE LEVEL
INPUT
SUBWOOFER
LEVEL
SPEAKER LEVEL OUTPUT SPEAKER LEVEL INPUT
LL
CC
RR
ON AUTO
1234
5
6
7
8
9
CONTROLS AND THEIR FUNCTION
6
Amplifier/Subwoofer SUB125
SCS125/125a SPEAKER LEVEL CONNECTIONS
SPEAKER LEVEL OUTPUTSPEAKER LEVEL INPUT
LL
CC
RR
SUB125
Receiver
Left Front
Left Surround
Right Front
Right Surround
Center
Left Front
Left Surround Right Surround
Right Front
Center
7
Amplifier/Subwoofer SUB125
SCS125/125a LINE LEVEL CONNECTIONS
SUB125
Receiver
Left Front
Subwoofer
Out
Left Surround
Right Front
Right Surround
Center
Left Front
Left Surround Right Surround
Right Front
Center
R
L
R
L
LINE LEVEL
INPUT