TL Audio VTC - Manual (Page 44)

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apparent on various paths. Two valve positions, along with their associated trimmers and IC’s, are
intentionally not fitted to PC345.
The master front backplane, PC336, is linked to the input bay backplanes, PC337, by short IDC
cables carrying the balanced busses. These cables plug into the underside of the PCBs, to avoid
fouling the input modules. It is unlikely that these cables will need to be removed, but if it should be
necessary, all of the input bay modules should be removed from the console, and the IDC cable
disconnected from the socket on the underside of PC337. The backplane can be lifted clear of the bay
after removing the six screws which secure it to the cradle. The IDC cable must be fed through the
bulkhead, and can then be removed. When refitting the cable, ensure that the plug is fully seated into
the socket on the underside of the PCB.
The majority of the Master section inputs and outputs are via IDC cables connected to the underside
of the upper backplane, PC355. The IDC cables are terminated on the jacksocket connector PCBs on
the rear panel, or taken to the patchbay. Note that the IDC cables are held in place with clips on the
console frame, and their function identified with labels on the cables themselves and the silk screen
of PC355 (e.g. “Groups”, “Inserts”).
4.2. Master Module Circuit Description.
Refer to the Master module block diagram in the specification section of this manual, the circuit
diagrams, and the expanded block diagrams in the following sections. The expanded block diagrams
include the locations of the various circuit blocks, and main signal names as used on the circuit
diagrams.
4.3. Master L+R Outputs.
Refer to the expanded block diagram, fig 3.
The L+R mix amplifiers are hybrid designs, using a low noise balanced IC first stage on PC336
followed by a valve stage on PC345. Due to the length of cabling that would otherwise be necessary,
a L+R sub-mix is formed on the upper Master section, consisting of the stereo return, MixB to L+R
path, talkback and oscillator. The sub-mix is buffered and balanced, and routed via the upper
backplane, PC355, into the main mix on PC336 by the signals ANC L and R.
The mix busses are connected to the mix amplifiers IC16 and IC17 (see CD1336 sheet 4), via the
IDC cables at CN4 and CN5 (from the input modules), CN6 from the group fader modules and CN2
from the ancillary sub-mix. The first stage mix amplifier outputs “L VIN” and “R VIN” are routed
via CN1 to the valve stages on PC345, from where they are returned on the same connector as “L
VOUT” and “R VOUT”. These signals are immediately routed out to the insertion points by the
signals “L SND” and “R SND”, via CN2 and PC355. The insertion returns “L RTN” and “R RTN”
are routed to the L+R master fader module, PC339, as signals “L FDR” and “R FDR” via the Master
module IDC cable fitted to CN4. The buffered post fade signals “L WPR” and “R WPR” are returned
on the same IDC cable to PC336, and thence to the output stages on PC355 as signals “L OUT” and
“R OUT”.
The output stages are shown on CD1355 sheets 2 and 3. There are separate buffered stages for the
balanced outputs at a nominal level of +4dBu and the unbalanced outputs at a nominal level of -
10dBu. The balanced outputs have a trimmer for balance, RV5 and RV6. The L+R level trimmers are
located at the valve stages on PC345 - refer to the calibration procedure for setup instructions. The
output level is monitored by the meter controller as signals “MTR L” and “MTR R” on PC355.