gain of about 2dB giving an open circuit output voltage of –8dBV for solo and –14
dBV for main channel signals.
The coupling between the output of each first amplifier (Terminal A), and the
input of the corresponding second amplifier (Terminal B) is made through a chain of
three resistors in series on the Solo Relay board. The total value of these is about
20k
Ω
, which is equal to the value of the feedback resistor in the second amplifier
thereby producing unity gain. The Solo Relay board is described in 12.24.
Pressing a solo button not only injects signal from that microphone channel
into the left loudspeaker channel as described above but also short circuits the solo
control bus bars. This causes four transistors to be switched on to provide low
impedance connections to the 0V line from the resistor junctions in the two coupling
chains of three resistors. This effectively switches off the normal monitor signal in
both channels and leaves only the solo signal in the left hand loudspeaker channel.
7.2.7 Control Room Loudspeaker Switch
This provides for the following:
(a)
Off.
(b)
Left (both channels on left loudspeaker).
(c)
Right (both channels on right loudspeaker).
(d)
Stereo (each channel or corresponding loudspeaker).
(e)
Parallel (both channels on both loudspeakers).
In positions (b), (c) and (e) above the signals from the two channels are
mixed by connecting together the Amplifier P outputs which are built out with 5.1k
Ω
resistors. Thus each provides a termination for the other. In position (d) each
channel requires a 5.1k
Ω
termination and these are provided on the switch.
7.2.8 Loudspeaker Quiet – Remote Control
An Amplifier J described in 12.11 follows the loudspeaker switch in each
channel. This serves two purposes, firstly it raises the level from –20 to –10dBV.
Secondly it contains three transistors each of which, when it is turned on, quiets the
loudspeaker. One of these is turned on when a track announce button is operated
and this reduces the loudspeaker level about 23dB. The second of these is turned
on when the operator uses the talkback. The amount of quieting can be adjusted by
a screwdriver operated preset control, which has a range of from 4dB to 20dB. The
third is turned on when the artist manager uses the talkback. There is a preset
control with a similar range. The two preset controls are ganged pairs operating on
both channels and are located just above the control room monitor level control.
Another output is taken from the Amplifier J to the correlator switch. This is not
affected by the quieting circuits but is provided with a series resistor to prevent low
loading when the correlator switch is operated.
7.2.9 Loudspeaker Quiet – Direct
A key is provided just above the record/replay key for quieting the
loudspeakers without use of the normal level control. This also has a pre-set
