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Section IV
CIRCUIT DESCRIPTIONS
INTRODUCTION
This Section details the circuitry of the Inovonics Model 261 Digital
Utility Audio Processor. Circuit descriptions refer to the four pages
of Schematic Diagrams contained in the Appendix, Section V.
Component
Annotation
Schematics for the 261 may appear to have component reference
designations assigned in a haphazard manner. Rather than anno-
tate the
schematic
in a logical sequence, we have instead chosen to
designate the
components
on the main circuit board in a logical top-
to-bottom and left-to-right manner, following the physical placement
of the parts in rows. It is our expectation that this practice will
make any necessary troubleshooting easier, as a component can
physically be located quickly following analysis of the schematic.
With respect to the SMD components on the plug-in DSP board,
good luck!
This is a multilayer board with microscopic parts on
both sides and some circuit points completely inaccessible. I sup-
pose this is one of the great benefits of the rapid progress in our in-
dustry.
ANALOG INPUTS AND OUTPUTS
Analog Line
Input
Referring to the left program channel (which is identical to the
right), IC11A and IC11B are unity-gain buffers for the differential
(balanced) analog program line input. The
attenuator associated
with the circuit board gain-range jumper, JP2, delivers a balanced
drive to pins 31 and 32 of the DSP board via main-board connector
J9.
Jumping up to the DSP board, the balanced program input is buff-
ered and single-ended by IC5B, and then fed to the analog left-
channel input of IC1, a DSP support chip that provides all A-to-D,
D-to-A and AES/EBU digital signal conversion functions.
Analog Line
Output
Pin 51 of IC1 is the single-ended, left channel D-to-A output. A cor-
responding DC reference comes out on pin 57. These D/A pins are
fed differentially to IC4B, which filters, amplifies and buffers the
analog program audio delivered to the main board on pin 4 of main-
board connector J9.
Back on the main board, IC9B performs additional filtering and
drives the monolithic balanced line-driver stage, IC8. This device is
intended exclusively for professional audio applications and contains
