REVISION C
BMX SERIES III CONSOLE
81
PACIFIC RESEARCH & ENGINEERING
The interrelationship of these five sections is best understood by referring to the module block diagram
located in Section 7.1.9 of this manual.
SLATE TONE OSCILLATOR
Pressing the SLATE button causes a high output from U15A, which is connected to one input of U20A.
When a Producer’s remote SLATE button is pressed, the output of U15B, which is connected to the other
input of U20A, goes high. Either input will cause a high output from U20A to the base of Q1, which
drives opto-isolator U12, and a15 volts to the slate oscillator supply line. The output of U20A
is also connected to the base of Q2, which pulls the Control Room monitor mute bus low.
The low frequency slate tone is produced by function generator U13, which generates a 30 Hz signal
whenever the supply line is energized. The frequency of the signal is determined by timing capacitor
C78 and resistor network R115, R117 and R116 (the frequency trimmer). The output of U13 is taken
from pin 2 (the distortion at this point is about 2% and there is a modest keying transient). This signal
is applied to bandpass filter U14B to eliminate the keying transient and reduce the harmonic distortion.
This filtering also shapes the envelope rise and fall time. The frequency of this filter is determined by
C82, C83, R122, R120 and R121, the tuning control. Additional filtering is provided by R118, C81
and R119. The output of the filter is routed to the front panel SLATE TONE level control, and then to
slate relay K7.
As soon as the slate oscillator supply line is keyed on, a positive voltage is applied to comparator U14A
via diode CR11. The output of the comparator switches slate relay K7 on. Therefore, when the slate tone
is requested, K7 immediately switches on and 200 milliseconds later the output of the bandpass filter
builds up and provides tone into the slate relay. The output of the relay is routed to the out position of
the front panel OSC button switch via R123. When the OSC switch is in the out position, the slate tone
is connected to buffer amplifier U11, whose output may be routed to Program, Audition, and Utility.
When the slate oscillator supply line is keyed off, function generator U13 immediately stops oscillating,
and the ringing output of the bandpass filter decays over a 200 millisecond interval. Shortly thereafter
the C76 discharges through R109, and the comparator output goes negative to de-energize slate relay
K7. The overall sequence is: whenever the slate tone is keyed on, relay K7 is immediately energized
and the slate tone builds up in amplitude; when the slate tone is keyed off, the tone is allowed to decay
and then relay K7 is switched off.
Pressing the console SLATE button also keys on the console’s electret microphone. While the button
is pressed, U15A presents a high to the time-delay network using R143 and C106. The network output
is applied to U18A about 40 milliseconds after the SLATE button is pressed. The output of U18A goes
high, energizing relay K1A, and routing console microphone to the “out” position of the OSC switch.
When the Producer’s SLATE button is pressed, the slate tone and the Producer microphone are keyed
on. Pressing the button causes a high output from U15B, which is routed through delay network R145
and C107 to U18B. As with the console slate system, about 40 milliseconds after the Producer’s SLATE
button is pressed, the output of U18B goes high. This operates the Producer microphone, keying relay
K1B, and the signal is routed to the “out” position of the OSC switch.