6
THEORY OF OPERATION
1. Overview
The AM-30P is a five channel, 175 Watt, surround-sound powered Acoustimass
®
loudspeaker,
designed to be used with either the CD-20 or CD-5V Music Center. The AM-30P and CD-20
together form the complete Bose
®
Lifestyle
®
30 home theater audio system. Major features of
the AM-30P include:
• Patented Acoustimass speaker technology
• Five independent high efficiency Class-G power amplifier channels
• Patented (VideoStage
®
) surround-sound decoder
• Microcontroller based remote control operation
• Patented low frequency dynamic equalization
• Miniature Jewel Cube
®
satellite speakers
• Manually adjustable bass and treble tone controls
The bass module portion of the AM-30P is identical to the AM-25P and similar to the AM-5 II
Acoustimass loudspeaker, except that the woofers are 8
Ω
instead of 4
Ω
, wired in parallel and
driven as a single channel. The acoustic response has been modified for powered speaker
application. The Jewel Cube satellite speakers have been specially designed to work exclu-
sively in equalized powered speaker applications .
The following theory of operation relates to the electronic module. The electronic module
consists of two printed circuit boards (referred to as the “Main” and “Amplifier” PCB) and a
magnetically shielded power transformer. Each PCB will be discussed separately. First, a
general operation and block diagram overview will be given (See Figure 8 block diagram),
followed by a detailed description of each diagram block that will reference the schematic
diagram.
2. GENERAL OPERATION AND BLOCK DIAGRAM OVERVIEW
Connection to the CD-20 occurs through a 30 ft. shielded audio cable that carries the following
signals:
• Left and right stereo audio (shielded)
• Turn-on signal (10VDC)
• Serial data signal
Figures 1, 2, and 3 show the total system frequency response, from DIN input to speaker
output, for the left, right, center, surround, and bass channels.
2.1 General Audio Chain (Refer to Figure 8 PCB Block Diagram)
Audio is buffered and amplified by the DIFF-AMP stage and then passed through a preliminary
equalizer stage COMMON-EQ. Next, the audio is passed through a volume control dependent
dynamic equalizer stage (consisting of the blocks labeled 37HZ BPF and DYNAMIC EQ VOL)
and then presented to the digitally controlled master volume control stage. This is followed by
an analog treble control stage (manually adjustable potentiometer). Next, the surround sound
decoder splits the left and right channel audio into five components: left, right, center, sur-
round, and bass. Within the decoder block, center and surround channels pass through sepa-
rate digital volume controls. The bass channel output is fed to an adjustable level control. Each
of these channels pass through separate equalizer stages, and then exit the Main PCB to the
power Amplifier PCB where they are amplified and sent to each speaker.
