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BMX SERIES III CONSOLE
4.7.2 Circuitry
The input signals are supplied by the three Stereo Line Output Amplifiers, and are selected by the front
panel MONO SOURCE switch and connected to variable gain amplifier U1. The voltage gain of U1
is adjusted by the front panel GAIN TRIM control, and has sufficient range to adjust the output level
from +4 dBu to +8 dBu. The output of U1 is connected to line output plug-in amplifiers A1 and A2,
operating as a push-pull pair to provide balanced drive to the output lines.
4.8 MONAURAL OUTPUT/TELCO MIX MODULE
The Monaural Output and Telco Mix sections of this module function independently. The Monaural
Output section is described in Section 4.7.
4.8.1 Function
The Telco Mix section produces up to three unique output mixes from the two telephone caller inputs
and a selection of the PROGRAM, AUDITION or UTILITY bus. The module receives its inputs from
those Stereo Line Input Modules designated as Telco inputs, and creates a unique output for each caller
which includes the selected bus plus any other caller except the caller's own voice (i.e., "mix-minus").
Each mix-minus output may be bandpass limited with internally switchable filters for improved hybrid
operation (reference Section 2.9.5).
NOTE: In order to assign a caller to the PROGRAM, AUDITION and/or UTILITY output buses (such
as the PROGRAM bus for "on-air" Telco operations), the desired bus must be selected on the Stereo
Line Input Module being used as the caller's Telco input.
The Telco Mix Module also creates a "monitor mix", which is the summed inputs of all callers. This
mix may also be used for applications where it is desired to create one or more custom mix-minus
foldback mixes or CUE feeds.
4.8.2 Circuitry
The inputs for the two telephone input module signals are routed to the front panel TELCO 1 and
TELCO 2 INPUT selectors. A monaural mix of each of the three main console outputs is connected
to the SEND TO TELCO switch. The output of this selector is buffered by input amplifier U601B
operating at unity gain to provide a level of -10 dBu to the mix-minus matrix.
The Telco monitor mix matrix consists of resistors R603 and R703 and mixing amplifier U601A.
Amplifier U601A operates with a voltage gain of 10 dB resulting in a nominal output level of 0 dBu,
which is connected to the front panel MONITOR control and the MONITOR OUTPUT terminals.
NOTE: The two Telco mix-minus circuits are identical, thus only the Telco 1 path is described.
The Telco 1 mix matrix consists of resistors R614 and R615 and summing amplifier U602B operating
at unity gain.
PACIFIC RESEARCH & ENGINEERING
REVISION C
77
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