TL Audio VTC - Manual (Page 49)

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routed via IDC cables and PC355 to the sub-mix on PC349 in the upper Master Module. The sub-mix
adds in the locally sourced AFL signals from the Aux Send Masters and Stereo Returns. The signal
“PFL L OUT” and “PFL R OUT” are routed back via PC355 to the Control Room and Studio output
PCB, PC352, located on the lower Master Module front panel.
4.12. Control Room Output.
The AFL/PFL mix has a +/-20dB gain trim stage at IC1A and IC1B (CD1352 sheet 3), before being
passed to the switch array that forms the Control Room source selector. The main sources available
to the Control Room are the L+R mix, MixB, and the external inputs 2TA, 2TB and EXT. Selection
of the main sources is additive (i.e. more than one may be selected at a time), but they are muted
when PFL is active or when the Studio output is soloed.
The Control Room source mix is formed at IC8B and IC8A (left and right respectively). These
amplifier stages have their gain modified by -3dB when Mono mode is selected, and are followed by
a -12dB gain reduction at IC4B and IC4A when the Talkback “On” button is active (even if talkback
is not routed to any destination - this enables a “Control Room Dim” function to be obtained, without
talkback).
The Control Room level is determined by RV2, followed by the +10dB buffers IC2A and IC2B. The
signals “CR L” and “CR R” are routed to the output driver stages on PC355, and the output jack
socket PCB or patchbay. Switching to alternative loudspeakers and power-on speaker thump
protection delay is achieved on PC355 by two relays, RL1 and RL2 (see CD1355 sheet 4). “ALT
LS~” is a logic control signal, whilst “PSU MON” is linked to +15V at CN11 on PC355. The
alternative loudspeaker outputs are located on the meter controller (see below), and remain on the
rear of the console when the patchbay option is specified.
The Control Room signal path switching is under logic control from PC351 - see below.
4.13. Studio Output.
The studio sources are selected in a similar manner to the control room outputs, in this case at IC23B
and IC23A. There is an additional Studio “On” switch controlling IC16, and talkback to the studio is
added at IC17B and IC17A. The Studio level is determined by RV3, followed by the +10dB buffers
IC3A and IC3B. The signals “STUDIO L” and “STUDIO R” are routed to the output driver stages on
PC355, and the output jacksocket PCB or patchbay.
4.14. Logic Control.
The Control Room, Studio, Talkback and Solo Modes are all controlled by the logic circuitry on
PC351. This PCB is mounted adjacent to the square push button switch array on the lower Master
Module front panel. Refer to CD1351.
The square push button switches are all momentary operation and are manufactured with a short
wiring loom and four way PCB header, enabling easy service replacement without soldering. All of
the switches are identical, and may be freely interchanged (but note cap colours!). The switch
functions are marked along the edge of PC351. Switch LEDs may be replaced from the front of the
panel by carefully pulling off the coloured cap and diffuser, and extracting the old LED with a pair of
small nosed pliers. The replacement LED should be carefully aligned with the locating tab in the
switch body, and pushed fully down into the switch. When replacing the switch cap, note the
orientation of the two small slots in the cap which must be aligned with the protrusions on the white