SA-2 and SA-3 Theory of Operation
General Information:
The Lifestyle
®
SA-2 or SA-3 stereo amplifier provides you with a simple solution when you want to add Bose
®
non-powered environmental speakers or Bose non-powered accessory speakers to your Lifestyle
®
system.
Bose proprietary Integrated Signal Processing technology, featured in the amplifier, provides full, rich stereo
sound, even when the speakers are playing at low volumes. By using the Lifestyle
®
stereo amplifier to expand
your system, you can enjoy Bose quality sound and Lifestyle
®
system convenience in your yard, patio,
swimming deck, garage, or utility room.
The Bose
®
Lifestyle
®
SA-2 and SA-3 amplifiers are a zone 2 accessory to the Bose Lifestyle
®
systems (see
repair package for installation instructions) and Bose
®
speakers. Lifestyle
®
Systems that use a music center
require an additional RF remote control in order to operate the second zone. This is because the dip switches
located in the remote control must be set differently to control zone 2 (see repair package for settings).
Lifestyle
®
systems that use a PMC/MRI (such as the Lifestyle
®
40 and 50) do not require an additional remote
control.
Note:
The circuit operation described below is for the left channel. The right channel operation is identical. The
designators inside the brackets are schematic sheet grid locations.
Refer to schematic for the following information.
The rear panel of the Lifestyle
®
amplifier utilizes two different types of audio input jacks, RCA and
DIN. These jacks, along with an audio input cable, part number 272902-220 supplied with the
amplifier, allow the use of the different Lifestyle
®
music centers. Different Lifestyle
®
systems require different
installation, see the repair package for the installation to the system you are working with.
Bose
®
link
is the proprietary networking technology that allows a Lifestyle
®
system to integrate with other Bose
products to provide sound in secondary rooms.
Introduction:
The Lifestyle
®
Stereo Amplifier 2 and the higher power Lifestyle
®
Stereo Amplifier 3 product use the same
printed circuit board. The LSA-2 is a depopulated version of the SA-3. The differences between the two
products can be summarized as follows:
Feature
LSA-2
LSA-3
Power
output
40W/ch 100
W/ch
Amplifier
topology
Class
AB
Class
G
Auxiliary
RCA
input
No
Yes
Mono/Stereo
switch
No
Yes
General Theory of Operation:
Refer to the system block diagram (Figure 1).
Audio Chain:
Audio Input is received at the DIN connector in the form of two separate analog stereo (left and right) channels
(channel 1 and channel 2) from the music center. The LSA-3 has a third audio input, via the left and right RCA
jacks. Channel selection, volume level, and dynamic equalization occur at the volume control IC U3 (the ST
TDA7309). Output from this IC is fed to a differential pre-amplifier stage, and then to the power amplifier IC.
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