Amplifier G in the cue channel associated with the main channel under
consideration, this being a point, isolated from the main channel, which has the
correct signal level at a low source impedance (see 5.3).
The “input to main” position derives its signal from the output of the Amplifier
C1 at the input to the Main Cassette and therefore measures the signal level after
the input gain control.
In the “Check Group”, “Check CRM” and “Check SP” positions the “check”
switches in these cassettes are brought into circuit for making measurements. The
“Check CRM” and “Check SP” positions only apply in the extreme left hand Main
Cassette. In the case of “Check Group”, groups 1A, 1B are available in the extreme
left hand Main Cassette and groups 2A, 2B are available in the adjacent Main
Cassette.
In the “external” position connection is made to SK6, a 5-pin Tuchel socket.
This facility can be of use in tracing faults in the Mixer and also for measuring levels
from other pieces of equipment. For example if SK8 is connected to SK4 or 5 by a
suitable jumper, the actual output level can be measured. If this is other than 10dB
above the level indicated when switched to “Record”, then there is probably a fault
in the relevant Amplifier G or R or output transformer or the wiring thereto.
In the “Oscillator” position connection is made to the –10dBV oscillator bus
line. Under these conditions, with the oscillator attenuator at 0 the V.U. meter
should also read 0. The frequency characteristics of the Amplifier U plus V.U. Meter
can be checked by varying the oscillator frequency and observing the meter
reading. The 10dB and 20dB boost can be checked by setting the oscillator
attenuator to –10dB and –20dB and pressing the corresponding boost button when
the meters should again read 0.
5.6
Power Supply
The power supply is identical with that used in the Microphone Cassette.
The Main Cassette consumes about 42mA at +20V and 78mA at –20V.
6.
TRACK MONITOR CASSETTE
6.1
Function
This cassette has eight inputs which can accept the replay outputs of up to
two 4-track tape machines. It provides facilities for routing these to microphone
channels for re-recording and also to the control room monitor and studio playback
channels.
6.1
Inputs
Four 5-pin Tuchel input sockets are provided each of which carries two
channels. The upper pair is designated Machine No. 1 and the lower pair Machine
No. 2. As seen from the back of the Mixer, the right hand pair carries channels 1
and 2 and the left hand pair channels 3 and 4. For 8-track working the second
Track Monitor Cassette will carry tracks 5 to 8 on the inputs marked 1 to 4
respectively. These inputs feed eight screened input transformers the primary
windings of which are floating. Since these are intended to accept nominally zero
