Infinity BU-120, HTS-20 Service manual
BU-120/HTS-20
Powered Subwoofer
SERVICE
MANUAL
Infinity Systems Inc.
250 Crossways Park Drive
Woodbury, N.Y. 11797
1-800-553-3332
A Harman International Company
Rev G 6/2001
Amplifier/Subwoofer BU-120/HTS-20
SAFETY INFORMATION
Warning
Any person performing service of this unit will be exposed to
hazardous voltages and the risk of electric shock. It is
assumed that any person who removes the amplifier from this
cabinet has been properly trained in protecting against
avoidable injury and shock. Therefore, any service
procedures are to be performed by qualified service personal
ONLY!
Caution
This unit does not have a power switch. Hazardous voltages
are present within the unit whenever it is plugged in.
Before the amplifier is plugged in, be sure its rated voltage
corresponds to the voltage of the AC power source to be
used. Incorrect voltage could cause damage to the amplifier
when the AC power cord is plugged in. Do not exceed rated
voltage by more than 10%: operation below 90% of rated
voltage will cause poor performance or may shut the unit off.
List of SafetyComponents Requiring
ExactReplacements
F1 Fuse SLO BLO 1.0A 250V 20mm.
UL approved
Leakage/Resistance Check
Before returning the unit to the customer, perform a leakage
or resistance test as follows:
Leakage Current. Note there is no power switch on this unit.
When the power plug is plugged in, the unit is live. Connect
the unit to its rated power source. Using an ammeter,
measure the current between the neutral side of the AC
supply and chassis ground of the unit under test. if leakage
current exceeds 0.5mA, the unit is defective. Reverse the
polarity of the AC supply and repeat.
Resistance. Measure the resistance from either side of the
line cord to chassis ground. If it is less than 500k ohms, the
unit is defective.
WARNING! DO NOT return the unit to the customer if it fails
one of these tests until the problem is located and corrected.
PWRCORD SPT-2 or better with polarized plug, UL
approved wired with the hot side to fused side.
Use with factory replacement panel strain relief
only.
T1 Transformer. Use only factory replacement.
DBR or D1 Bridge diode. Use only factory replacement.
C1, 2 4700uF, 50V electrolytic filter caps. Be sure
replacement part is at least the same working
voltage and capacitance rating. Also the lead
spacing is important. Incorrect spacing may
cause premature failure due to internal cabinet
pressure and vibration.
C6 10uF 50V electrolytic radial* BU120 and HTS-20 rev. A only.
S53AMI or CN1 Power output module. Use only factory
replacement
Faceplate Faceplate. Use only factory replacement
Air leak cover Use only factory replacement
CMC1 Use only factory replacement
L1 Use only factory replacement
Fuse PCB Use only factory replacement
* See Service Bulletin (INF2000-01 REV 2) page 15.
Main PCB Use only factory replacement
R29 470Ω .25W METAL OXIDE, non flammable
IMPORTANT SERVICE NOTES: When testing the BU120/HTS-20 Series amplifier, a load must always be
connected to the output terminals, whether the woofer, or a 4 to 8 ohm resistive load.
All AC powered test instruments (meters, oscilloscopes, etc.) must have a floating ground, i.e. be
connected to an isolation transformer.
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Amplifier/Subwoofer BU-120/HTS-20
TABLE OF CONTENTS
SAFETY INFORMATION...............................................................2
GENERAL SPECIFICATIONS.......................................................3
DETAILED SPECIFICATIONS ......................................................4
CONTROLS AND THEIR FUNCTION ..........................................6
BU-120/HTS-20 CONNECTIONS..................................................7
OPERATION ................................................................................11
BU-120/HTS-20 TEST SET UP AND PROCEDURE .................12
BU-120/HTS-20 POWER AMP MODULE
TESTING FLOW CHART ............................................................13
SERVICE BULLETIN INF9902 Rev 1 - FEBRUARY 2001 .........14
SERVICE BULLETIN INF2000-01 Rev 2 - FEBRUARY 2001 ....15
TECH TIPS .................................................................................16
BU-120/HTS-20 PACKING & CABINET ASSEMBLY................17
BU-120/HTS-20 AMPLIFIER ASSEMBLY
EXPLODED VIEW ......................................................................18
BU-120/HTS-20 rev. A PCB (revision 3.52)
Component Side Trace...................................................20
BU-120/HTS-20 rev. A PCB (revision 3.52)
Solder Side Trace...........................................................21
BU-120/HTS-20 rev. A PCB (revision 3.53)
Component Side Trace...................................................22
BU-120/HTS-20 rev. A PCB (revision 3.53)
Solder Side Trace...........................................................23
BU-120/HTS-20 ELECTRICAL PARTS LIST.................24
BU-120/HTS-20 IC DIAGRAMS .....................................25
BU-120/HTS-20 SCHEMATIC 1 of 2 .............................26
BU-120/HTS-20
HTS-20 REV B ELECTRICAL PARTS LIST
HTS-20 REV B CIRCUIT BOARDS.................................31
HTS-20 REV B SCHEMATIC...........................................33
HTS-20 REV B POWER AMP MODULE SCHEMATIC...34
SCHEMATIC 2 of 2 .............................27
....................28
GENERAL SPECIFICATIONS
Frequency Response (± 3dB) .................30Hz – 150Hz
Output (RMS).............................150W
Driver ..................................12"Woofer
Crossover Frequency .......................50Hz ~ 150Hz (continuously variable)
Dimensions (HxWxD).....................14½"(36.8cm) x 14 ½" (36.8cm) x14 ½" (36.8cm)
Add 1 ¾" (4.5cm) for feet.
Weight..................................43lbs/19.5 kg,
Refinements may be made on occasion to existing products without notice,
but will always meet or exceed original specifications unless otherwise stated.
REGARDING SERVICE FOR THE INFINITY HTS-20 SUBWOOFER
There are two versions, an "A" and "B", with minor internal differences.
Data for both versions is included, and differences noted in the following pages.
Units can be identified for service as follows:
Amplifier faceplate says "Made in Canada" on the "A" version.
Amplifier faceplate says "Made in China" on the "B" version.
3
Amplifier/Subwoofer BU-120/HTS-20
DETAILED SPECIFICATIONS
LINE VOLTAGE Yes/No Hi/Lo
Line
US 120vac/60Hz Yes 108-132 120 Vrms Normal Operation
EU 230vac/50-60Hz Yes 207-264 230 Vrms Normal operation, MOMS
Asia 100vac/50Hz No 90-110 100 Vrms Normal Operation
Parameter Specific
ation
Amp Section
Type (Class AB, D,
other)
Load Impedance
(speaker)
Rated Output Power 150 Watts 150 1 input driven
THD 0.3 % 1 22k filter 75w (Power Bandwidth
THD @ 1 Watt 0.5 % 0.8 22k filter
DC Offset 10 mV-DC 20 @ Speaker Outputs
Damping factor 100 DF 50
Input Sensitivity
Input Frequency 40 Hz Nominal Freq. 1 input driven
Line Input 63 mVrms ±2dB To Rated Power/ Vol @
Speaker/Hi Level Input 4.8 Vrms ±2dB To Rated Power/ Vol @
D n/a n/a Class D Preferred...Sink
4 Ohms n/a Nominal Z-curve required
Unit QA Test
Nom. Unit Notes
required
Conditions Notes
Limits
required for Class AB
30-100Hz)
1 input driven: AP source
Max
Max
Z = 600 ohms
1 input driven: AP source
Z = 25 ohms
Signal to Noise
SNR-A-Weighted 100 dBA 90 Relative to rated output A-Weighting filter
SNR-unweighted 75 dBr 70 Relative to rated output 22k filter
SNR rel. 1W-unweighted 65 dBr 55 relative to 1W Output 22k filter
Residual Noise Floor 3 mVrms 4 Volume @max, using
RMS reading on A/P
Input Impedance
Line Input 10k ohms n/a Nominal
Speaker/Hi Level Input 200 ohms n/a Nominal
Filters 0dBr = 1w @ 50Hz
Low Pass (fixed or
variable)
Low Pass filter (point or
range)
Slope 18-24 dB/Octaven/a
Subsonic filter (HPF) 34 Hz ±2dB -3dB Point
Slope 24 dB/Octaven/a
Variable
50-150 Hz ±2dB -3dB Point
22k filter required due to
100kHz switching noise
present at speaker output
4
Amplifier/Subwoofer BU-120/HTS-20
Limiter (yes/no) yes
Max. Output
Power/THD=10%
150w/10%P
-max/TH
D
Features
Phase Switch (yes/no) yes — functional
Volume pot Taper
linear — functional
(lin/log)
Input Configuration —
Line In
L,R — functional
(L,C,R,AC3,Mono)
Line Outputs (L,C,R) L,R — functional Buffered Output /
Spkr/Hi Level In
(L,C,R,mono)
L,R — functional
Spkr Out: Hi Pass Filter 100 Hz functional
functional Maximum Output Power Maximum THD as a result
of limiting.
Enabled w/Line/Spkr Input Select Switch
Pre-Volume control
Enabled w/Line/Spkr Input Select Switch
8 ohm Satellite: 6dB/oct
passive xover
Driven from zero ohms
source impedance
Signal-Present LED Yes — — — Bi-Color LED
(green=signal/ red=no
signal)
Signal-Present Input
Freq.
100 Hz functional Nominal 200uF Series Cap on
PCB
Signal-Present Level 35 mV functional 100Hz into Line Input w/
1 ch. driven
Power on Delay time <2 sec. AC Power Applied
Transients/Pops
Turn-on/off Transient 500 mV-peak 2v-pp @ Speaker Outputs AC Line cycled from OFF
to ON or ON to Off
Efficiency
Stand-by Input Power 14 Watts @ nom. line voltage
Power Cons.@rated
110 Watts @ nom. line voltage
power
Efficiency 136% % Relative to rated output
Protection
Short Circuit Protection yes functional Direct short at output
BU120
Line
Fuse Rating 1.0 Amps Type-T or Slo Blo
HTS-20
Line Fuse Rating 2.0 Amps Type-T or Slo Blo
5
Amplifier/Subwoofer BU-120/HTS-20
BU-120/HTS-20 CONNECTIONS
When connecting your subwoofer make sure you turn
all the power off.
There are several ways to connect your subwoofer.
Read this section carefully to determine which method
is best suited for your installation.
The subwoofer may be fed directly with a low-level
signal taken from a preamplifier's output by using the
second set of output jacks on the rear of the
preamplifier (See Figure 1). If a preamplifier has only
one set of outputs, you may use two (2) “Y” connectors
(See Figure 2) to connect the subwoofer. Use
standard shielded leads terminated at each end with
male RCA connectors. Connect one end of each
stereo pair of leads to the preamplifier's left and right
outputs and connect the other end to the
corresponding left and right LOW-LEVEL INPUTS (1)
on the subwoofer.
If you are using a tube preamplifier and the connecting
leads will be longer than 10 feet (3 meters), we
recommend not using the above connection method. A
tube preamplifier may not be able to handle the
capacitance introduced by leads more than 10 feet in
length. Instead, try using the high-level connection
methods listed on pages 5-7.
Figure 1.
preamp's output by connecting second set of
output jacks to the rear of your amplifier.
Figure 2.
connectors) if your preamp has only one set
of outputs.
- A low-level signal can be used from a
- You can use this method (2“Y”
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Amplifier/Subwoofer BU-120/HTS-20
When using a single subwoofer, you MUST use a pair of stereo low-level leads from your preamplifier's outputs. When using
two subwoofers, one for the left and another for the right channels, connect the left preamplifier output to BOTH the left and
right LOW-LEVEL INPUTS of the subwoofer used for the left channel by using a Female-to-Male “Y” connector at the
subwoofer's output. Connect the right-channel preamplifier output to both jacks of the right-channel subwoofer in the same
manner (See Figure 3). If the preamplifier has a mono subwoofer output, you'll also need a Male-to-Female “Y” connector to
split the mono signal to the subwoofer pair (See Figure 3).
Figure 3.
The subwoofer may be connected to your system using the
HIGH-LEVEL INPUTS (4) on the plate located on the rear
panel of the subwoofer. Use speaker wire, maintaining
proper polarity (+ to + and - to -). Attach the speaker wire to
the left and right HIGH-LEVEL INPUTS on the subwoofer
and the other ends to the proper left and right OUTPUTS on
your amplifier or receiver (See Figure 4).
If you plan to use two subwoofers (one for the left and the
other for the right channel), connect wires from the left and
right OUTPUT on your power amplifier or receiver and
attach the other ends to the corresponding HIGH-LEVEL
INPUTS on each subwoofer. Observe polarity (See Figure
4).
Figure 4.
subwoofer.
- Use this method when using a single subwoofer output or two subwoofers.
- Use this method when using a single
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Amplifier/Subwoofer BU-120/HTS-20
Figure 5.
subwoofers.
- Use this method when using two
Figure 6.
one subwoofer to satellites.
Depending on whether you are using one or two
subwoofers, connecting your satellites can be
accomplished in one of two ways. If you are using a
single subwoofer with a pair of satellites, connect
them as shown in Figure 6.
- Use this method when connecting
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Amplifier/Subwoofer BU-120/HTS-20
Figure 7.
connecting two subwoofers to
satellites.
If you are using two subwoofers as a
stereo pair with a pair of satellites, connect
them as shown in Figure 7.
BU-120
The subwoofer has a variable frequency
control that can be used to block unwanted
frequencies (between 50 - 150Hz) from
being reproduced by the subwoofer.
When you set this control depends on the
low-frequency capabilities of your satellite
speakers. Adjust this knob to the lowest
frequency that you satellite speakers were
designed to reproduce (refer to Operation,
step 7).
HTS-20 - Has no external control. If you are
using a receiver or surround processor
containing a Dolby Digital and/or DTS
decoder, set the crossover bypass switch
to "On". If you are using a stereo or Dolby
Pro Logic receiver, set this switch to "Off";
this places the preset roll-off crossover
frequency point at 100Hz.
- Use this method when
10
Amplifier/Subwoofer BU-120/HTS-20
OPERATION
Setting the Controls
1. Initially set the subwoofer's Volume control to the minimum
position.
2. BU120 - Initially set the subwoofer's Crossover Frequency
control to 12 o'clock.
HTS-20 - If you are using a receiver or surround processor
containing a Dolby Digital and/or DTS decoder, set the
crossover bypass switch to "On". If you are using a stereo
or Dolby Pro logic receiver, set this switch to "Off"; this places
the preset roll-off crossover frequency point at 100Hz.
3. Set the subwoofer's Phase switch to the "0" position.
Turn the Power On
4. Turn on the entire audio system and play any music
source.
5. Turn the Volume control to its mid position. If no sound
emanates from the subwoofer, check the AC line cord and
input cables. Are the connectors on the cables making proper
contact? Is the AC plug connected to a “live” receptacle?
Adjusting the Volume
6. Set the overall volume control of the preamplifier or stereo
to a comfortable level. Adjust the subwoofer's Volume control
until you obtain a pleasing blend of bass. Bass response
should not overpower the room but rather be adjusted so
there is a harmonious blend across the entire musical range.
Many users have a tendency to set the subwoofer volume too
loud following the belief that a subwoofer is there to produce
lots of bass. This is not entirely true. A subwoofer it there to
enhance bass, extending the response of the entire system
so the bass can be felt as well as heard. However, overall
balance must be maintained; otherwise, the music will not
sound natural. An experienced listener will set the volume of
the subwoofer so its impact on bass response is always there
but is never obtrusive.
Room Placement
8. The room placement of the subwoofer is the most critical
aspect of its installation. It will be necessary for you to try
various locations in your listening room before you choose
the final location. Some possible starting points include:
behind the right channel satellite speaker, along the back
wall between the satellites, along a side wall (but not too
close to a corner), or behind a couch or a chair.
In general, the closer the subwoofer is to wall and corners,
the greater the effect of low-frequency enhancement.
Experiment with the Crossover Frequency and Volume
controls in different locations until you are pleased with the
result you obtain from your particular application.
A Word of Advice
The Low-Frequency Roll-off and Volume controls may be
set anywhere within their rotation. However, it will be a most
unusual circumstance if you have to set the Volume control
completely clockwise. This may indicate an unbalanced
condition in your system (too much bass) or an especially
large room, or room placement may not be correct. Try
several other locations before concluding that the Volume
control must be set at maximum.
A Word About Tone Controls
The tone controls on your electronic components
(preamplifier, receiver, etc.) should be used with the utmost
discretion. Excessive boost can create severe power
demands on your power amplifier. Maximum bass boost
can create a demand for literally hundreds of watts in the
bass region, whereas in the “flat” position, or with the tone
controls switched out of the system, your average listening
level may be impressively and realistically loud at less than
10 watts. The remaining power capacity required is on
reserve for power peaks on sharp transients and powerful
crescendos.
The Crossover Frequency Controls (BU120
only)
7. The Crossover Frequency control sets the high-frequency
roll-off, adjustable from 50 to 150Hz. Where you set this
control depends on the low-frequency capabilities of your
satellite speakers, system placement, and other factors
affecting the mid-bass region. Turn the control UP
(clockwise) until you feel there is too much mid-bass
information (around 100Hz), then back the control down a bit
until that area sounds more natural. To hear more low bass,
turn the Crossover Frequency control DOWN a bit and the
Volume control UP by about the same amount. This will
increase low bass while leaving the mid-bass sounding the
same as it did before the adjustment. To reduce low bass
without changing midbass, turn the Crossover Frequency
control UP and the Volume control DOWN. Switch the Phase
switch between “NOM” and “REV” positions while listening to
music. The selection that sounds the best is the correct
adjustment for your system.
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