Radio Systems Millenium-A Analog Console, Installation And Operation Manual

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Radio Systems Millenium-A Console Page 48
The VCA is a current in, current out device, which may provide amplification as well as attenuation of the signal from
U3C. The VCA is capable of over 100 dB of level control, depending upon the control voltage applied to pin 3 of the
VCA. The front panel linear taper fader supplies a control voltage ranging from +7.5v at the minimum setting of the fader
to 0 volts at the maximum setting. This voltage is applied to the positive input of U7B which serves as a buffers. Resis-
tors R75 and R76 attenuate the buffered control voltage to levels acceptable by the VCA. Transistors Q5 and Q6 in con-
junction with resistors R78 and R79 shunt R76 to convert the linear fader taper into a three slope audio taper approxima-
tion. The turn on points for Q5 and Q6 are determined by the fader setting and the voltage reference on the bases of Q5
and Q6. U7A and resistors R74 and R77 add a negative offset to the control voltage so that the VCA is at unity gain at
normal fader settings, and is supplying 15dB of gain at the maximum fader setting. In addition, U7A drives both left and
right channel VCAs to maintain proper channel tracking. VR2 is the VCA distortion null adjustment. Integrated circuit
U8A converts the current output from the VCA into a voltage.
Integrated circuit U10 is a 4053 analog switch which connects the output of U8A to the mix buses as determined by
voltages from the Input Control Board which are applied to U10 pins 6, 9, 10, and 11. Pin 6 must be low in order for
the signal from U8A to reach any mix bus. Pulling pin 9 high (+7.5v), in conjunction with pulling pin 6 low, will place the
signal from U8A onto the mono mix bus. Similarly, pulling pin 10 or pin 11 high will place the signal onto the audition and
program mix bus respectively. Since pins 9, 10, and 11 operate independently from each other, any combination of mix
buses may be selected at the same time.
7.4 Monitor Control Board
7.4.1 Brief Description
The Monitor Control Board is mounted on the right-hand side of the console lid and provides the following functions:
1. Monitor select logic and indicators, headphone select logic and indicators.
2. Interface between logic levels and those required by the Output Board.
3. Interface between the Monitor, Headphone and Cue level controls and the VCA’s located on the Six Channel
Input Board.
4. Clock Timer interface and Timer Auto Reset and Start logic.
5. Eight position accessory switches and associated LED’s
7.4.2 Detailed Description
Microcontroller U3 has five ports (RA, RB, RC, RD, and RE). Ports RA, RB and RE are configured as outputs, the oth-
ers as inputs. The output port signals are as follows:
RA0 Low when the Program Bus is selected for headphones
RA1 Low when the audition Bus is selected for headphones
RA2 Low when the Telephone Bus is selected for headphones
RA3 Low when the Cue Bus is selected for headphones
RA4 Low when the Timer Auto Reset and Start functions are enabled
RA5 Low when External Input 1 is selected for headphones
RE0 Low when External Input 2 is selected for headphones
RE1 Low when External Input 3 is selected for headphones
RE2 Low when External Input 4 is selected for headphones
RBO Low when the Program Bus is selected for the monitor
RB1 Low when the Audition Bus is selected for the monitor
RB2 Low when the Telephone Bus is selected for the monitor
RB3 Low when the Cue Bus is selected for the monitor
RB4 Low when External Input 1 is selected for the Monitor
RB5 Low when External Input 2 is selected for the Monitor
RB6 Low when External Input 3 is selected for the Monitor
RB7 Low when External Input 4 is selected for the Monitor