signal bus is fed with signal from the channel in which the button is pressed, through
a 16k
Ω
resistor. The solo signal bus is connected to the left hand channel terminal
B interconnection, between the Solo Relay board and the Amplifier P board. It
therefore feeds into the virtual earth amplifier BT4, VT5 of Amplifier P, which has a
feedback resistor of 20k
Ω
. This amplifier thus gives a gain of 2 dB so that a –
10dBV signal produces a –8 dBV output signal. This is higher than the nominal
level at this point in the Amplifier P but it produces a more acceptable sound level
from the single loudspeaker fed from a single channel.
12.25 Re-Record Attenuators
12.25.1
Purpose
These provide the 25dB of attenuation which is required for a re-record signal
which leaves the Track Monitor Cassette at a level of –10dBV to be applied to the
Microphone Cassette input switch at the required level of – 35dBV.
12.25.2
Circuit
The circuit diagram is shown on Drawing No. AE230.
12.25.3
Circuit Description
One board serves both channels of a Microphone Cassette. It contains 10
identical attenuators the inputs being on two sets of terminals numbered 1 to 5 and
the corresponding outputs being on two sets of terminals numbered 6 to 10.
Separate 0V lines are provided, to be connected to the 0V lines of the two channels
in the cassette.
The input impedance of each attenuator is about 38k
Ω
so that when, in a 24-
input mixer, 12 of these are connected in parallel, each A1 amplifier in a Track
Monitor Cassette which feeds one of the Mic. Input Bus Lines will have a load
impedance of just over 3k
Ω
. The output impedance of each attenuator which, when
in use, becomes the input impedance of an Amplifier D, is about 2k
Ω
.
12.26 Track Announce Relay
12.26.1
Purpose
One of these is located in each Main Channel Cassette. It is designated RL5
in the Block Schematic DE1. It receives a control signal (+6V) from the Studio
Playback Cassette and provides the currents require to operate two Amplifiers N.
12.26.2
Circuit
The circuit diagram is shown on Drawing No. AE231.
12.26.3
Circuit Description
The circuit is identical with that of VT7 and VT8 of Active Relays (see 12.23.2)
with the exception that the 150k
Ω
resistor connected to the base of the first
transistor is in this case returned to the common emitter point and not to a +9V line
