Broadcast Electronics 3000 Series - Cue Track Audio and One Kilohertz Stop Sensor; Optional Three Kilohertz Stop Sensor

Signal from the level control is coupled through C30 (C31) to
the output booster
IC-3. This dual amplifier and the complementary symmetry
drivers Q4, Q3 (Q1, Q2) provide 28 dB gain to drive the output to a maximum
+18 dBm. This gain is determined by R42 (R47), R41 (R46). DC bias for Q3,
Q4 (Q1, Q2) is provided by CR4, CR5, CR6 (CR1, CR2, CR3). Bias for IC-3 is
supplied from the divider R16, R17, C10 through R40, R49 and internal voltage
directly from the +24 VDC.
The fully amplified signal is coupled through C22 (C21) to the
primary of the output transformer
and the headphone jack. (The transf0rmer
adds 6 dB of gain to the output signal which then appears at the output
connector).
4-4.
CUE TRACK AUDIO AND ONE KILOHERTZ STOP SENSOR
The cue track of the playback head is coupled through C15 to the
input of
IC-2A which acts as a preamplifier with gain and equalization com-
parable to the program preamplifiers as provided by R21, R22, R23 and C14.
Bias for IC-2A is supplied through R15 from voltage divider R17 and R16.
The output of the preamplifier is direct coupled to the booster
IC-2B. Inverting amplifier IC-2B provides 27 dB of gain as determined by
R27 and R28. The amplified signal is coupled through C20 to the cue output
(on the rear panel remote control connector) through pin 19 and to the 1 kHz
sensor level control (R8).
The signal is coupled through C43 to a fixed tuned twin-T filter
composed of IC-4A, R84, R85, R86, C44, C45 and C46. The 1 kHz output of the
filter is ac coupled to half wave rectifier CR21, CR22. Capacitor C58 and
resistor R97 provide filtering. The FET Q10 is connected to ground the
signal to
disable the sensor. In the stop mode, the gate of Q10 grounds to
the
stop/start logic through CR15 and R100 to turn on Q10. When the ground
is removed as the logic changes to the run mode, C55 keeps Q10 in conduction
(and the sensor muted) for approximately three seconds. Similarly, the gate
of
Q10 can ground through R95 and CR17 to the fast forward cue shift/mute
bus. Removing this ground activates the sensor immediately.
The de signal from R75 is connected to comparator IC-6D. When
this voltage exceeds the reference from R57, R99, connected through R72,
the output of IC-6D goes to +VDC to deliver a pulse through C39 to the stop
control.
4-5. OPTIONAL THREE KILOHERTZ STOP SENSOR
In units equipped for operation at both the normal and fast for-
ward (3X normal) speeds, a 3kHz stop sensor is also installed. Signal is
taken from the 1 kHz level control (R8) to FET Q7. In this case the sensor
is active only when the FET is conducting. This is accomplished by ground-
ing the
fast forward cue shift/mute bus.
The mute is gradually removed as C34 discharges through R55.
Even if the tape is not up to full 3X normal speed, a stop tone can be
sensed, since the normal 1 kHz sensor is slowly turning off as the 3 kHz
sensor is turned on. When the ground is removed, Q7 immediately shuts off
to disable the 3 kHz sensor.
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