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BMX SERIES III CONSOLE
Control Room bus, and also drives U216C via time delay network R253, R254, C229 and CR203. The
output of inverter U216C drives Talkback relay K5 at pin 6.
The other Talkback functions operate in a similar fashion. One of the input control lines is pulled low
by a push-button switch, the appropriate output from A/B selector U200 will then be low, and the logic
in U203, U204, U205 and U206 will pull down the appropriate control bus, dim the monitor, engage
the Talk circuit, and mute the signal from being on program lines at the same time. This logic design
also prevents a microphone from Talking to its own location.
With Sends
Send relay K2 is energized through Q228. When internal option switch S206 is ON, Sends are always
active with PRE-fader selection, regardless of the ON/OFF status of the module.
4.3 STEREO LINE INPUT MODULES
This section describes the function and circuitry of both the Stereo Line Input Module (PR&E #99-263)
and the Stereo Line Input Module With Sends (PR&E #99-253). Schematics for both modules are
located in Chapter 7.
4.3.1 Function
Both Stereo Line Input Modules will accommodate nominal input levels from -12 dBu to +8 dBu. The
A/B input selector allows for the selection of either of two stereo inputs. Separate logic controls are
available for each input for the remote control of tape machines and/or other sources, and the INPUT
MODE switch allows for the selection of a STEREO, MONO, LEFT or RIGHT source to be sent to
the output assignment switches.
4.3.2 Circuitry
NOTE: Except for the presence or absence of the Send circuitry, the two Stereo Line Input Modules
function identically. The additional Send circuitry is described at the end of the audio and logic circuit
descriptions.
AUDIO
NOTE: The stereo audio path consists of two identical sets of circuitry. For clarity and simplicity, only
the left channel is described below.
The input to the module is a balanced, symmetrical input, instrumentation amplifier. This amplifier
is configured with three operational amplifiers, contained on plug-in function amplifier A1, operating
with a cross-coupled input stage feedback gain trim control. The voltage gain range from module input
to the output of the amplifier is -18 dB to +2 dB. The gain trim control is adjusted to provide a level
of -10 dB to the Patch Output line.
PACIFIC RESEARCH & ENGINEERING
REVISION C
70
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