Bose FreeSpace Business E4 II Series Service Manual page 91

THEORY OF OPERATION
Power Amplifier
Refer to the power amplifier channel block diagram below for the following information.
The E-4 Series II power amplifier section employs a number of protective devices and commu-
nication circuits to ensure continued reliable operation, and to enable reporting and logging of
any fault conditions. In addition, there are several measurement circuits, whose primary purpose
is to provide information to Bose ® FreeSpace ® Installer™ software, enabling it to verify proper
configuration of the E-4 Series II unit itself, and the speakers connected to it. The block diagram
provides a simplified view of one of the four channels, however many of the peripheral functions
are shared with one or more other channels. Refer to the schematics for more information on
exactly how the circuitry and functions throughout the units various PCB assemblies.
The power amplifier module itself consists of a single heatsink assembly with two circuit boards
mounted to it back-to-back. The upper PCB contains amplifier circuitry for output zones (chan-
nels) 1 and 2; the lower PCB contains amplifier circuitry for output zones 3 and 4, plus power
supply components shared by the entire unit. The power amplifier module receives analog
inputs and 2-way serial communications from the E-4 Series II DSP and host processor sections
via a 34-pin ribbon cable. Power is also supplied from the Amp/PS module to the rest of the unit
via this cable.
Component designators in the block diagram refer to channel 4, see the schematic diagram to
find appropriate designators for other channels. The core of the power amplifier section is a pair
of high voltage MOSFETs (Q10 and Q11). These are driven by a "Class T" hybrid control mod-
ule from modulation pattern to drive Q10 and Q11's gates. Contained in the hybrid module itself
are a proprietary analog/DSP IC operating from a single +5 volt supply, and a pair of high
voltage half-bridge gate drive chips including charge pumps for high-side drive. There are also
other discrete components to perform level translation, gain scaling, buffering, etc.
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