Output Board Circuit Description; Brief Description; Detailed Description - Radio Systems Millenium-A Analog Console Installation And Operation Manual

Radio Systems Millenium-A Console
U3 sets the state of its output ports depending on the signals (switches) present at its input ports (RC and RD). U2 and
U4 converts the output of U2 to the BCD format required by the analog switches on the Output Board. Transistors Q1,
2, 3, 4, 6 and 7 provide an interface between the logic level signals and those required by the Output Board. Transistors
Q5 and Q8 interface the Timer Auto Reset and Start signal with the Clock/Timer. Transistor Q9 turns on (under control
of U3) to prevent the Auto Reset and Start signal from reaching the Clock/Timer. Eight accessory switches and LED's
are brought out at J1 and J2 for user remote interface. Current limiting resistors for the LED's are user-installed into
header J5.
The voltage from the wiper of the Monitor, Headphone and Cue level controls is filtered and scaled to proper VCA levels
by the associated capacitor and resistors.
7.5

Output Board Circuit Description

7.5.1

Brief Description

The Output Board performs the following functions;
1. Summing mix bus current to voltage conversion
2. Differentially balanced audio output amplifier
3. Differential meter amplifiers
4. Peak detectors and LED drivers
5. Input selection of headphone and monitor amplifier signals
6. Level control and muting of monitor amplifier signals
7. Level control and power amplification of headphone signals
8. Level control and power amplification of cue signal
9. Talk back control and interface
10. Drivers for Mute 1, Mute 2, and timer reset
11. Power supply distribution to the Six Channel Mixer Boards
7.5.2

Detailed Description

Five of the six summing buses in the console are similar to each other. These are left program, right program, left
audition, right audition, and mono. The sixth mixing bus for the cue channel will be discussed separately. Integrated
circuit U14B is utilized as a unity gain current to voltage converter for the left program mixing bus. The output of U14B is
routed to the headphone and monitor select CMOS analog switches as well as to VR7 for adjustment prior to receiving
20dB of amplification from U7A. U7A drives the + left program channel output while U7B inverts the output of U7A and
drives the -left program channel output. Integrated circuit U2A, diodes Dl thru D4 and the associated resistors convert
the balanced left program channel output to a floating D.C. voltage to drive the left program VU meter. Therefore, the
effects of loading the console output or erroneously grounding one of the console outputs will be reflected on the VU
meter. Trimmer VR2 provides "0" VU adjustment for a range of console outputs. Differential amplifier U2B converts the
meter voltage from floating to single ended prior to applying the voltage to U15A. Integrated circuit U15A functions as
a peak detector with the trip point adjusted by VR12. When the positive peak of the audio signal (applied to U15 pin 4)
becomes more positive than the reference set by VR12 the output of U15A will go to -15 volts and in turn the output of
U15B will go to -15 volts and illuminate the peak LED. At the conclusion of the peak U15 pin 4 will fall to lower potential
than the reference set by VR12, and the output of U15A (which is an open collector) will allow C59 to be charged by
R115. When the potential at U15 pin 9 is more positive than the reference at U15 pin 8 the output of U15 B will go high
and the LED will extinguish. Capacitor C59 and resistor R115 act as a .5 second peak stretcher which allows the LED to
properly illuminate.
Integrated circuit U12A converts the cue mix bus signal to a voltage and then the signal is routed to the headphone and
monitor select CMOS analog switches, and to the cue VCA. Integrated circuit UlA allows an external signal (such as talk
back) to be summed onto the cue summing bus. VRl allows adjustment of the external signal.
The monitor amplifier circuitry is identical for the left and right channels. So only the left channel will be discussed.
Integrated circuit U20 is a 4051 CMOS analog switch. U20 is a single pole, eight position switch. Eight inputs are con-
nected to U20 which selects one input depending on the voltages present on U20 pins 6, 9, 10, and 11, and routes the
selected input to U20 pin 3. Four of the inputs to U20 come from the output of the mix bus current to voltage converters.
These are left program, Left Audition, Mono, and Cue. In addition, there are four external inputs (A thru D) which are
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