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The present invention avoids an increase in system power consumption when switching from two
stereo outputs to five surround sound outputs. The audio system comprises a power supply input
Vcc (pin 3), an audio input (pin 7, pin 11) and an output to drive the audio speaker according to
a selected one of at least two operating modes of the audio speaker. It has a plurality of
amplifiers 52, 54, 56 having (pin4, pin2). It is used in an entertainment system having internal
and external speakers and associated amplifiers for switching between stereo and surround
sound modes. At least two separate power supply voltages 34V, 24V are supplied to the
amplifier, and switch elements Q1, Q2 operate in response to switching between modes, one or
the other of the separate power supply voltage sources, at least two amplifiers Connect to one of
the power supply inputs. [Selected figure] Figure 3
Control device Detailed description of the invention
The present invention relates to audio playback devices, and in particular, the present invention
relates to a system switchable between modes in which an audio amplifier is selectively activated,
for example for switching between stereo mode and surround sound mode.
Conventional technology
Switching amplifiers between AC supply voltages are known to be effective in certain situations,
and it is also effective to switch off the supply voltage to unused elements, unnecessary power
consumption and heat generation. It can be avoided.
For example, the SGS Thomson Microelectronics TDA 7294 Class G power amplifier is specified
for dual bipolar supply voltages.
Relatively small amplitude positive and negative supply voltages are typically connected to the
power output stage of the amplifier.
When the amplitude of the input voltage exceeds the threshold, it is automatically switched to a
large amplitude supply voltage instead of a small amplitude voltage.
This accommodates the necessary swing in the output voltage of the amplifier without clipping
and reduces the average power consumption of the amplifier. This is because, for a given output
current at low amplitude, there is a small voltage drop across the output transistors, resulting in
less power consumption than at a high amplitude supply voltage. Effectively, the TDA 7294
amplifier has two different rated powers and automatically adjusts between the two rated
Home entertainment systems are known, and multiple audio outputs are provided to drive
speakers that may have various modes of operation. Monophonic audio signals require one
speaker, and stereo signals are usually arranged laterally, with two speakers being arranged in
front of the viewer or other audience. Also, the surround sound configuration has at least one
pair of speakers placed laterally in front of the audience, and the second pair is placed laterally
behind the audience.
The audio signals to these speakers are sometimes driven by different signals in a subtle manner.
This is by using a combination of channel separation, phasing and echo to provide a listening
effect that can realistically mimic performance attendance in the audience, or other effects as
desired by the program provider.
In order to be able to provide surround sound signals, the entertainment system requires audio
amplifiers and speakers for each of the positions of the speakers in each mode. Typically, there
are at least five channels, amplifiers and speakers, including front left, center front, left rear and
right rear.
Not all programming involves a surround sound signal. The user may, for example, choose to
operate in stereo mode or mono mode, even if the programming is capable of stereo or surround
sound operation, if the necessary speakers and wiring are not installed. Preferably, the system is
switchable between these modes.
Usually, entertainment systems such as currently available home theater systems at least have a
built-in stereo power amplifier and a speaker mounted in a housing. Systems capable of surround
sound operation have additional built-in audio power and connector couplings for driving
external speakers.
The amplifier and speakers can support external left rear and right rear surround speakers for
use with the internal front speakers, or alternatively, the user is inevitably in addition to the
external rear speakers , And may choose to use external speakers to carry the left front, right
front and center front channel signals. This requires a large number of amplifiers.
By menu selection or the like, the user can configure the system to reflect the operating mode
used. For example, the user can disable the surround sound feature if the back speaker is not
It is generally accepted in the audio arts that the average power output of each active channel of
a multi-channel system must be equal for optimal system performance. When the audio output
levels applied to each channel or each speaker are equal, switching from a mode that does not
use channels and speakers to a mode that uses many channels and speakers effectively enables
the audio output power that is emitted increase.
Typically, user menu selections or other controls allow balance adjustments applicable to
multiple axis volumes and one or other modes of operation (e.g. left / right balance and front /
back sounds disappear) Go). The amplitude of the input signal to each amplifier can be switched
automatically on mode change.
There are various needs addressed by the system as described above, including enabling
switching between modes using speaker and output volume adjustments when changing between
modes. However, what such systems can not provide is an effective technique for managing the
power consumption when switching between modes.
Previous systems wastefully supply voltage to audio power amplifiers that may not be fully used
in certain operating modes, and / or despite differences in output power required as a function of
the selected mode The same power is supplied to the audio power amplifier in each mode to bias
the level.
The inventive solution is provided for an audio system having a plurality of amplifiers.
Each amplifier provides a supply input, an audio input and an audio to drive the audio speaker
according to one of at least two operating modes, wherein the selection of the audio speaker and
/ or the required power output of the audio speaker differ between modes. It has an output. The
invention can be used, for example, in entertainment systems having internal and external
speakers and associated amplifiers for switching between stereo and surround sound modes.
At least two separate power supply voltage sources are provided for the amplifier, and the switch
element operates in response to switching between modes, one or the other separate power
supply voltage source, each of the at least two amplifiers. Connect to one power supply input.
Preferably, the switch element disconnects all voltage sources from the unused amplifier in one
or more modes.
This reduces or eliminates power consumption by the amplifier and effectively regulates the
output level of the amplifier. For example, when switching from two stereo outputs to five
surround sound outputs, the total audio power of the system is not increased.
The present invention can switch or respond to user selection or other reasons to accommodate
certain modes, and can disconnect power from the amplifier for unused internal and external
According to one aspect of the invention, an audio system as described above is provided with
alternating power supply levels for each amplifier used in each audio mode.
By switching the input voltage to the amplifier, the output amplitude of each channel is adjusted,
reducing or eliminating the need to support volume level adjustment specific to each mode.
The system preferably has the same audio total output power in stereo mode with internal
speakers, as opposed to audio total output power in stereo mode with external speakers, and the
same in surround sound mode with five speakers Has audio full output power. When switching to
a mode that does not use a special channel, this same amplifier power switching technique
eliminates power consumption by the non-selected channel amplifier.
An audio reproduction apparatus embodying one aspect of the present invention includes a
plurality of audio amplifiers, each amplifier responsive to a corresponding audio signal to
generate audio power at a corresponding audio speaker. When the supply voltage generated by
the second audio amplifier of the plurality of audio amplifiers is high, in the first operation mode,
the small amplitude supply voltage is supplied to the first audio amplifier of the plurality of audio
amplifiers. Applied. When the supply voltage generated by the second audio amplifier is low, in
the second mode of operation the supply voltage has a large amplitude. This is in such a way that
the variation in the total audio power generated is reduced when changes in the operating mode
Embodiment of the Invention
Referring to FIG. 1, an exemplary home entertainment system 20 includes a central stereo
speaker (center speaker) 26, a left stereo speaker (left speaker) 24 and a right stereo speaker
(light speaker) 25. A built-in audio speaker and cabinet 22 are generally provided. The
entertainment system 20 preferably includes the ability to drive an additional speaker 32
external to the cabinet 22.
For surround sound audio mode, the cabinet speakers 24, 25 (and optionally 26) are added by
the rear speaker 32 located behind the area 40 normally occupied by the user or the audience
Ru. The user preferably has the choice to use an external front speaker 27, 28 which is used in
addition to or in place of the speakers 24, 25 provided in the cabinet 22.
The speakers provided in the entertainment system are generally grouped into left-to-right, and
front and rear categories, and receive control (not shown) in which the speaker output is
balanced to the user's preferences. Typically, balance control changes the output level of the left
speaker to the light speaker. The fader control can similarly change the output level of the front
speaker to the rear speaker.
In combination, for example, in monaural mode, using only the center speaker only, or using both
the left speaker 24 and the light speaker 25 of the cabinet (or using a group of speakers driven
from the same signal) or separated The speakers may operate in stereo mode using one or more
pairs of left and right speakers using the channel signal.
In the preferred embodiment, in monaural programming, it is connected to the left and right
speakers 24 and 25 of the cabinet which provide the same signal in that mode.
Stereo is provided using an external front left speaker 27 and a front light speaker 28. In
surround sound mode, the speakers are usually driven by five separate channel signals: front
light, front left, front center, rear light and rear left channel signals. The latter two are connected
to the external rear speaker 32.
In surround sound mode, the rear speakers 32 may be driven by additional separated left and
right rear channel signals included in the program being received or played by the entertainment
system 20.
Alternatively, the rear speakers 32 may be driven by signals that are the result of processing of
the separated left and right stereo signals connected to the front speakers 27, 28.
In that case, an audio source is provided which is located in the area of the front speaker 42 but
which has an auditory path and a large space which causes the fading and echo effects similar to
the signal provided as a result of the above processing. As such, fading, delay or echo effects are
All speakers are driven from the outputs of audio amplifiers 52, 54 and 56 generally shown in
FIG. Audio amplifiers are grouped into pairs, but each channel potentially has a separate signal,
in which case separate amplifiers or channels are required.
The amplifiers 52, 54 and 56 are power amplifiers or output amplifiers and drive speakers. The
invention may also be applied to control the amplitude of the amplifier stages located upstream
of the output amplifier in a cascaded configuration. The amplifiers 52, 54 and 56 in the
illustrated embodiment may be, for example, Thomson Microelectronics model TDA 7265 or
The audio power amplifier can operate with bipolar supply voltages or can be unipolar as in the
illustrated embodiment. In order to adjust the invention to a bipolar supply configuration, the
single sided configuration shown is provided by a substantially mirror switching arrangement,
which when switched changes the supply voltage for both negative and positive supply voltages. .
Gain control (not shown) is provided in a known manner for volume, balance and fade, the user
sets the volume level and balances the relative volume level back and forth. Gain control can
include manually operated control elements such as potentiometers, etc., and can be connected
to a system controller as illustrated as a sound source.
This system controller adjusts the level in response to user selections made in the menu
technique, such as via an infrared remote control signaling unit, as required by the switching
matrix generally indicated by the signal bus in FIG. Connect the signal to the required amplifier.
Such user selection may also be based on generating a signal to switch the circuit of the present
invention between stereo mode and surround sound mode.
According to the invention, the audio system comprises at least amplifiers 52, 54 and 56 each
having a power supply input. In the illustrated embodiment, the left amplifier (L) and the right
amplifier (R) are paired with one power supply input for each dual amplifier package (surround
pair, front pair and rear pair) .
Each channel of each pair (i.e., each amplifier) has an audio signal input and an audio signal
output to drive a speaker. The amplifiers for the speakers 24, 25 permanently mounted in the
cabinet ("internal" speakers) are connected directly to the respective audio signals as shown in
The remaining amplifiers 54, 56 in the illustrated embodiment can be individually connected to
the external speakers 27, 28 and 32 by means of suitable connectors. Amplifiers 52, 54 and 56
drive the associated audio speakers to provide an audio power output level that is a function of
the gain of the respective amplifier, and the amplitude of the input signal connected to the
The audio system has at least two modes. In these two modes, one or both of the choices for
which the audio speaker is available and the choice of the required power output of the audio
speaker differ between the modes. The required power output of the amplifier, and hence the
required power output of the audio speaker, is a partial function of the supply voltage connected
to the amplifier.
According to an aspect of the present invention, at least two separate power supply voltage
sources are provided at least for an amplifier. In the illustrated embodiment, the power supply
voltage for the surround sound amplifier package for driving the external rear speaker is set and
can not be changed at the predetermined voltage Vcc. This voltage is preferably applied only in
the surround sound mode and is not applied in other modes or when the entire unit is turned off
and not powered up.
For the internal or main left and right speakers (cabinet speakers), the voltage applied to the
amplifier 54 and for the external front left and front light speakers, the voltage applied to the
amplifier 56 can be changed. In particular, two different supply voltages V1 or V2 and V3 or V4,
respectively, are provided, the at least one switch element 62 operating in response to the
control 64 according to the switch between modes, the individual power supply voltages One of
the sources is connected to the power supply input of the respective amplifier or amplifier pair.
Switch element 62 is operable in at least one of the modes of the system to disconnect all voltage
sources from the at least one amplifier. This removes power consumption by the amplifier.
According to an alternative embodiment, the amplifier and the speaker can operate in at least
two modes and an additional mode. FIG. 3 illustrates the audio amplifier and switched power
supply configuration of entertainment system 20, and illustrates the power source-amplifierspeaker configuration illustrated in FIGS. The same symbols and reference symbols indicate the
same components or functions.
According to the exemplary embodiments shown in FIGS. 2 and 3, the modes include mono,
stereo and surround sound modes of operation. This mode can optionally include one or more
modes entered by the setup procedure.
In the setup procedure, an option can be selected from the menu indicating that no external
speakers are connected to one or the other external speaker input, at which time the voltage
supply to the corresponding amplifier can be switched off. For example, the user can optionally
choose to use the surround sound mode, but with the front speakers used and the external
speakers 32 for the rear speakers, the main left speaker in the interior (cabinet) This mode may
be valid as it allows the above selection using 24 and the light speaker 25 (and the center
speaker 26 of the cabinet).
The switch element connects the amplifier to the low power supply voltage in at least one other
mode where a relatively large number of amplifiers and speakers are used, such as a surround
sound mode, and at least other using relatively few amplifiers and speakers. In the mode, it is
operable to connect at least one amplifier to the high power supply voltage. This has the effect of
reducing the audio power output per speaker in modes using a relatively large number of
amplifiers and speakers at low supply voltages.
In carrying out the functions of the invention, it is used to lower the power output per speaker,
eg more distributed without substantially increasing the total power output from all the speakers
used In an array, a relatively large number of speakers can be activated and used. Voltages V 1, V
2, V 3, V 4 and Vcc may be generated from one power supply (not shown) having a fixed
maximum rated power. The same fixed maximum rated power by providing lower voltage levels
when more speakers and amplifiers are energized, and higher voltage levels when fewer speakers
and amplifiers are energized. Is effectively maintained.
For example, when switching from using two speakers to using four speakers, and assuming that
the original two speakers are among the four speakers to be used, the switch element is Connect
a low voltage to the amplifier that drives the two original speakers. The switch element can
optionally connect or disconnect the supply voltage to the amplifiers for the other two speakers
to be used, and when not previously powered up in the other mode of operation Can be powered
Alternatively, the added speakers can be connected to an always powered amplifier, but only in
the mode with two added speakers, only the activation signal is applied. In this case, the
additional speaker amplifier should be selected so that minimal power is dissipated if the input
signal is not active.
The supply voltages to the two original amplifiers change when those amplifiers are used and
powered up to different numbers of loudspeaker members (decreased when switching from a
small number of active channels to a large number of active channels, Increase when switching
from many active channels to a few active channels).
In this way, the audio full power output of the speakers in the small group is approximately the
same as the audio full power output of the speakers in the large group, and each of the speakers
in the large group is not forcedly driven.
This configuration retains power compared to similar configurations where the power supply
voltage to the original speaker is not reduced. Power supply savings occur even if the amplitude
of the input signal to the switched amplifier is adjusted to use the amplitude of the signal as a
means to adjust the volume of the audio output. This is because there is a small voltage drop
between the output or the driver stage of the amplifier, resulting in less power consumption.
As mentioned above, the same fixed by supplying low voltage levels when voltage is applied to
more speakers and amplifiers, and by supplying high voltage levels when voltage is applied to
less speakers and amplifiers. Maximum rated power is effectively maintained. Thus, there is no
need to supply power at high power ratings in each mode of operation.
Although the preferred embodiment of the present invention switches from stereo mode to
surround sound mode, the same technique can be applied to other situations where changes in
the number of speakers and amplifiers used actively are made. . In the preferred embodiment,
the audio system has two main channel amplifiers and associated speakers, and the two external
channel amplifiers have audio outputs connectable to external speakers.
Another embodiment is an audio system having a main two channel amplifier with an audio
output connectable to a front stereo speaker, the two surround channel amplifiers having an
audio output connectable to a rear stereo speaker ing. The audio system may optionally have a
central channel speaker driven by at least one of the selectable amplifiers. Typically, the center
channel is used to monotonically drive both cabinet speakers in surround sound mode, and the
front and rear surround sound signals are directed to the front and rear pairs of external
The audio system 20 as shown in FIG. 1 can be a television chassis home entertainment system
and includes three stereo audio power amplifiers as shown in FIGS. 2 and 3 supporting different
configurations. There is. In the first mode of operation, i.e. internal stereo mode, 12.5 watts per
channel stereo amplifier 54 (i.e. two channel amplifiers) are connected to drive the two self
contained or cabinet speakers 24, 25.
In addition, 12.5 watts per channel stereo amplifier 56 are provided to connect to the two
external speakers 27, 28 which will be used as front speakers (see FIG. 1) at the user's option. If
an external speaker is used and the internal speaker is rendered inoperable, the use of the
external speaker can provide a second mode of operation (external stereo mode) to be compared
to the main internal stereo mode.
Or, the user chooses to use the cabinet speaker and the external front speaker simultaneously,
two stereo amplifiers power on the four speakers, and in internal mode there is one stereo
amplifier of the same rated wattage and two The audio total power level is doubled to drive the
cabinet speaker.
The third operation mode is the 5-channel surround mode.
In this mode, the two internal speakers 24, 25 carry the central front channel signal. Front
external speakers 27, 28 carry front left and front light signals. The third amplifier 52 applies
power to the left rear surround speaker and the right rear surround speaker 32.
Preferably, the user may select a switch input etc. by appropriate menu selection, and operates in
surround mode or stereo mode, or various combinations of internal and external speaker usage.
Such a selection may be valid even if a signal is available to drive the rear speaker 32 in a given
program or as a processed version of the front speaker signal. For example, the user may not
have wired the system to support surround sound. Or, if already wired, the user simply chooses
to use the system in a more restricted way than possible using all capabilities.
In full five-channel surround sound mode, per channel stereo amplifier described above, taking
into account the external front and rear speakers and using two built-in (cabinet) speakers 24
and 25 for the center speaker signal. With 12.5 watts, it is possible to power the main internal
stereo amplifier 54 and the external front speaker amplifier 56 using the same nominal supply
voltage to power both amplifiers.
The same 12.5 watt rated power is applied to the third stereo amplifier 52 and driven from the
nominal supply voltage to power on the rear surround speakers and the change from stereo
mode to surround mode increases audio power output by a factor of 3 Let
The relative power level of the center channel is twice that of any other channel. This requires
adjustment of the audio level. Even assuming automatic adjustment, the power supply is
effectively overdesigned for application.
According to the present invention's approach to this problem, the power supply level to the
amplifier is switched between the high voltage and the low voltage of AC to adjust the relative
power output of the channel, reducing power waste. Ru. As shown in FIG. 3, this can be
accomplished to have the same audio total output power and total power requirements as in
surround mode. Furthermore, according to the solution of the invention, the power output per
channel can be made equal in the surround sound mode for all five channels, and the power
supply capability is fully used in both modes.
The main stereo amplifier 54 of FIG. 3 (ie, the internal or cabinet speaker amplifier) is supplied
with +34 volts DC voltage through the saturation bipolar transistor Q2. The switch Q2 conducts
in stereo mode only, ie "on" and in this mode connects the +34 volt DC supply voltage to the
power supply terminal 111 of the main stereo amplifier 54 for the base-emitter voltage drop. .
The switch Q2 is switched to the stereo mode by the output of the system control network of the
switch element 62. The control element can be connected to a sound source that is capable of
switching between stereo mode and other modes. Preferably, the output of the control element is
settable at the user's option in connection with a preset stereo operation.
Another supply voltage at +16 volts DC is connected to the power supply terminal of the main
stereo amplifier 54 through the diode D1. Thus, diode D1 is reverse biased in stereo mode,
preventing conduction from the +34 volt supply to the +16 volt supply.
In stereo mode, the main stereo amplifier 54 supplies 12.5 watts of per-channel audio power to
8-ohm speakers 24, 25 internally mounted to the two cabinets for +34 volt supply. The total
power output in this stereo mode is 25 watts.
In surround sound mode, switch Q2 is switched off and the +34 volt supply is disconnected from
the main stereo amplifier. The diode D1 is forward biased and supplies +16 volts to the main
stereo amplifier with less diode drop.
With this supply voltage, the main stereo amplifier 54 delivers only 2.5 watts per channel or 5
watts total. In this mode, the signal input to both parallel amplifiers in the main stereo amplifier
54 is preferably the same monaural signal, ie the center channel signal in the surround sound
mode from the sound source.
The external stereo amplifier 56 is supplied with +34 volts through another saturated bipolar
transistor switch Q3. Another blocking diode D2 is likewise connected to an additional DC supply
voltage of +24 volts. When switch Q3 is on (in stereo mode only), +34 volts is applied to the
external stereo amplifier 56 with less voltage drop between the base and emitter of transistor
switch Q3 in saturation.
The diode D2 is reverse biased, which prevents conduction from the +34 volt supply to the +24
volt supply. The external stereo amplifier 56 supplies a total output power of 25 watts in stereo
mode to 12.5 watts per channel to the external 8 ohm speakers respectively.
トランジスタスイッチQ3は、サラウンドサウンドモードにおいてスイッチオフされる。 The
+34 volt supply voltage can not conduct current to the external stereo amplifier. The diode D2 is
forward biased and supplies +24 volts to the voltage supply terminal of the external stereo
amplifier 56. This supply voltage supplies 5 watts for each channel, ie a total of 10 watts.
In this embodiment, the third amplifier, the surround amplifier 52, is supplied with +24 volts and
is not switched between voltage levels when changing between modes. The voltage can
optionally be turned on and off by additional switch means (not shown), but this amplifier 52 is
used only in the surround sound mode, and the main stereo amplifier and the external stereo
amplifiers 54, 56 As in the case it does not have to be switched to receive different power levels.
With the 24 volt supply shown, the surround amplifier 52 generates 5 watts per channel for left
and right speakers, rear or surround speakers.
According to the embodiment described above, the total output power of the amplifier operating
in the above described mode is 25 watts.
Since the power supply voltage is reduced when relatively many amplifier channels and speakers
are active, and the power supply voltage is increased when relatively few amplifier channels and
speakers are active, the present invention allows excessive power Provide effective power level
control to prevent consumption. Depending on whether the system is in 2-channel stereo mode
or 5-channel surround mode, the power supply is sufficiently stabilized and the output power
level in both of these modes will be the same.
In addition to the basic power supply switch configuration as described above, the embodiment
of the present invention shown in FIG. It comprises filter capacitors C1, C2 and C3 connected
between it and ground for disconnecting the amplifier.
Furthermore, each of the supply voltage inputs to the amplifier is connected to a voltage divider
to ground, defined by the resistors Ra, Rb.
The connection of the resistors Ra, Rb is connected to the bias input of the amplifier, and the
resistor Rb is connected in parallel with the capacitor Cb. That is, the resistor Rb is connected
between the bias input and the ground. When going from a low supply voltage to a high supply
voltage, capacitor Cb is energized through resistor Ra to smoothly raise the bias input voltage to
a reference voltage defined by the voltage divider equal to half the supply voltage.
Each of dual amplifier packages 52, 54 and 56 includes a pair of audio amplifiers, for example,
non-inverting amplifier 54a of amplifier package 54. The gain of amplifier 54a is established by
the pair of feedback registers 201 and 202 in a conventional manner. Resistor 202 is AC coupled
to ground via capacitor 202.
The half supply voltage generated at input terminal Bias is DC coupled to the non-inverting input
terminal of amplifier 54a. Because the resistor 202 is not DC coupled to ground, the DC gain of
the amplifier 54a is one. As a result, the DC component voltage at output terminal 204 is equal to
the half supply voltage generated at input terminal Bias. Thereby, a single-ended power supply is
used to generate an output voltage at terminal 204 with a DC component voltage equal to half
the supply voltage.
Each of the switch elements including transistors Q1, Q2, Q3 is turned off in surround sound
mode and turned on in stereo mode to control voltage switching. The switch element is
responsive to a controller status output that may be generated as a function of user selection of
stereo operation versus surround sound operation.
In addition to the switch elements shown for illustration purposes, additional switch elements
(not shown) can be used, for example, to disable the modes or amplifiers from one another
according to user selection and other factors, Internal and external speakers other than the
standard combinations described above can be combined.
For some surround program source types, such as Dolby Pro Logic surround, there is nothing
unique in the program material that gives a unique signature, in which case the selection can be
made at the user's option.
On the other hand, digital sources such as AC-3 have this ability to carry a signal representing
the mode in which the audio signal is encoded, and may automatically switch between stereo
mode and surround mode. It is possible.
FIG. 5 illustrates the physical layout of an entertainment system or the like according to the
invention, with a plurality of audio modes selectively adopting different combinations of audio
speakers. FIG. 6 illustrates a power supply switching arrangement according to one aspect of the
invention. FIG. 3 is a detailed circuit diagram illustrating an embodiment of the present invention
as generally illustrated in FIG. 2;
Explanation of sign
20: home entertainment system 22: cabinet 24: left stereo speaker 25: right stereo speaker 26:
center speaker 27, 28: external front speaker 32: additional rear speakers Q1, Q2, Q3: switch
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