level signals and since the normal internal working level of –10dB is required within
the Mixer, these transformers have a step down ratio of 3.16 : 1.
6.3
Re-Record
Two re-record selector switches are provided. The left hand one, S1, selects
tracks 1 and 2 (or 5 and 6) from Machine 1 (or from Machine 2). The right hand
one, S12, selects tracks 3 and 4 (or 7 and 8) from Machine 1 (or Machine 2). Both
these switches have central “off” positions. The outputs of these selector switches
feed general purpose attenuators which are calibrated from +10 to –30dB and “off”.
At this point, the terminology changes from that of track numbers to that of the re-
record input bus lines in the Microphone Cassettes.
The re-record selector No. 1 has this number on its knob and it feeds
microphone input bus lines 1A and 1B through level controls with knobs bearing
these inscriptions. Similarly for re-record selector No. 2, and for Nos. 3 and 4 if the
mixer has provision for 8-track working.
If the mixer has provision for auxiliary stereo working, another Track Monitor
Cassette is required of which only half is employed. By using a standard cassette it
acts as a spare for the multi-track positions.
In the auxiliary stereo Track Monitor Cassette the record selector knobs are
engraved 5 and -, the upper level controls are engraved 5A and 5B and the lower
level controls are unmarked. If, due to a fault, it is necessary to interchange
cassettes the knobs can easily be interchanged also.
6.4
Monitor Channels
Each Track Monitor Cassette contains four monitor channels.
6.4.1 Tape Machine Selection
Each Track Monitor Cassette is provided with a 4-pole change over key
which performs a function similar to the two re-record selectors. Since this key is
used in conjunction with the record/replay key to perform A/B checks on both tape
machines, it is located in the Control Room Monitor Cassette near to the
record/replay key but, to facilitate the understanding of its operation, it is shown on
the block schematic diagram of the Track Monitor Cassette, those leads thereto
which are external to this cassette being shown in broken lines.
6.4.2 Amplifier
The impedance of the secondary winding of the input transformer is about
200
Ω
. The tape machine selector switch which is followed by the record/replay key
(see 7.3.2) is followed by a nominally unity gain Amplifier G in which the overall gain
of the channel is trimmed.
Each monitor channel then consists of:
(a)
An Amplifier G to provide for trimming the gain of the channel.
(b)
A Band Pass Filter
(c)
A coupling capacitor
