Radio Systems Millenium-A Analog Console, Инструкция по установке и эксплуатации

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Radio Systems Millenium-A Console Page 47
RB3 High when the Audition Bus is selected
RB4 High when the Telephone Bus is selected
RB5 High when the Cue Bus is selected
RB6 High when the channel is on
RB7 High when the channel is off
RE0 High (momentary or maintained) to provide a remote control pulse or holding signal when the chan-
nel is turned on.
RE1 High (momentary or maintained) to provide a remote control pulse or holding signal when the chan-
nel is turned off
RE2 High (momentary) when the on button is pressed to generate a timer reset signal
U2 sets the state of its output ports depending on the signals (switch and jumper set) present at its input ports (RA, RC
and RD).
U3A, B and C “logic” and the selected buses with the channel on signal. U4, B and C provides an interface between the
logic level signals and those required by the Six Channel Input Board. U5 switches either its A or B inputs to its Y out-
puts depending on the state of the signal at U5 pin 1. U5 routes the proper Mute, Timer Reset and Ready Lamp signals
to their destination depending on the input selected (A or B). In similar fashion, based on the input selected, U1 selects
the proper pulse or holding signal to route to the user remote control.
See the “Six Channel Control Board” section for jumper selection and operational details.
7.3 Six Channel Audio Board Circuit Description
7.3.1 Brief Description
The Six Channel Input Board contains six identical stereo amplifiers which provide the following:
1. selection of the input signal
2. gain adjustment of the input signal
3. routing of the selected signal to the desired mix bus or buses
7.3.2 Detailed Description
The left and right channels are identical, so only the left will be discussed.
Left channel input A signals are attenuated 13dB by R1, R3, and R2 (or by R8, R7 and R9 for input B) before routing to
IC U1, a type 4052 analog switch. The amount of attenuation maybe varied by the installation of resistors into the DIP
component carriers provided, and then plugging the DIP component carriers into socket J3 for input A or J4 for input B.
Bridging R3 (or R9) would increase the attenuation while bridging R1 and R2 (or R8 and R7) would decrease the attenu-
ation. Adjusting the attenuation allows each input to accept signals ranging from microphone to high level.
Integrated circuit U1 selects either input A or input B depending on the voltage present on pin U1-10. A low on pin 10
will allow input A signals to reach the following circuitry. Input B will be selected if pin 10 is high. The voltage on pin10
is controlled by circuitry on the Input Control Board.
Integrated circuit U3 (sections A, B, and C) and transistors Q1 and Q2 form a differentially balanced instrumentation am-
plifier for left channel input signals. Transistors Q1 and Q2 are low noise devices which allow this circuit to operate with
microphone levels in addition to high level inputs. Transistors Q1, Q2, and integrated circuits U3A and U3D form a bal-
anced amplifier whose gain is determined by R28, R29 and R21. The gain may be increased by the installation of jump-
ers onto header J5 which would reduce the value of R21. A -7.5v reference is fed to the positive inputs of U3A and U3D
which in turn control the current through Q1 and Q2 so that the negative inputs of U3A and U3D also remain at -7.5v.
This feedback makes Q1 (Q2) a part of U3A (U3D) rather than an independent amplifier preceding the IC. Integrated
circuit U3B is a differential amplifier which converts the balanced signal from U3A and U3D to a unbalanced signal.
The signal from U3B is summed with right channel signal from U4C and routed to Q7 which will place this mono signal
onto the Cue Bus when the Q7 is tured on (by pulling its gate low) by the Input Control Board. In addition, the signal
also is routed to J7, a stereo unbalanced insert point, as well as header J7, which allows bypassing of the patch point,
and easy placement of a mixing channel into mono operation. In this case, the left input would feed both the left and the
right channel mix buses. The level at this point is nominally -4dBm. Integrated circuit U3C buffers the signal from the
insert point prior to IC U6, a dBx Voltage Controlled Amplifier (VCA).