7.2.2 Input Amplifiers
The bus bars selected by K2 are connected to the inputs of fixed gain
Amplifiers C2.
7.2.3 Monitor Selectors
These are two five position switches, one for each channel. Each has an
“off” position, a normal position, position for Cue 1 and Cue 2 and a synchronous
replay position.
In the normal position signals are taken from the outputs of the Amplifiers C2.
The cue signals are derived from the cue output circuits, which are located in
this cassette and are described in 7.6.
The synchronous replay signals are available on lines from the Studio
Playback Cassette (see 8.1.1) and the signals on the left and right can only be
switched to the left and right channels respectively.
7.2.4 Level Control
The selected signals pass through Band Pass Filters and coupling capacitors
to the Control Room Monitor Level control. This is a ganged control with 20 steps of
2dB calibrated from +20 to –20. There is no “off” position. Each of the
potentiometers has a total resistance of 3.2k
Ω
. The output level with the control at
zero is –30dBV.
7.2.5 Pole
A spring return push button is provided which when pressed reverses the
polarity of the signal in the right hand channel. The polarity change is effected by
using an Amplifier P, the circuit of which is described in 12.28. In each channel the
Amplifier P carries two separate amplifiers connected in series, both of which
introduce phase reversals. The first amplifier has a voltage gain of 16dB and the
second amplifier has unity voltage gain. Each amplifier output is built out with a
5.1k
Ω
resistor and, when actually used as an output, is terminated externally in
5.1k
Ω
, thereby introducing a voltage loss of 6dB. The overall voltage gain is
therefore 10dB and, since the input level is –30dBV, the output level is –20dBV.
In the left hand channel, the output of the second amplifier only is used, this
being in phase with the input. In the right hand channel the in phase second
amplifier output is the one normally used, but pressing the Pole Button changes
over to the phase reversed output of the first amplifier.
7.2.6 Solo
The solo bus line is connected to the terminal B of the Amplifier P in the left
hand channel. This terminal is coupled to the virtual earth input of the second
amplifier. Since the solo signal from a microphone channel is -10dBV signal fed
through 16k
Ω
, and since the feedback resistor of the amplifier is 20k
Ω
, there is a
