Q2 OPERATION AND MAINTENANCE MANUAL 9601 83
The VCA master module contains two VCA group master faders
and their associated cut switches. A reference voltage of -5V is fed
to the faders and applied to ICs 12A and B where it is offset by
a fraction of the original reference voltage. The output of the
ICs is fed via an enable switch to the VCA group buses from
where it will be received by modules assigned to that VCA bus.
The VCA group cut switch is a two pole switch. One pole is used
to illuminate the switch LED and the other switches the -5V
reference to the VCA buses to give a mute. The mute switch
feeds the buses after the VCA enable switch so that it can be
used even if VCA fader control is not selected.
The remainder of the module is taken up by a stereo effect
return. It is possible to select between input A and input B by
a switch, the output of which goes to IC1A and 2A, the balanced
input stages. Following the left side only the signal then goes
to a gain trim stage formed by IC1B and then through the LEFT
CUT switch. A width control is next formed by ICs 4A and 5A.
This stage may be bypassed when not in use. The left and right
signals are combined in this stage to give an image which can be
reduced from full stereo to mono and expanded again into stereo
but with the left and right channels reversed.
A phase reverse circuit formed by IC3A operates on the right
signal only and again is bypassed when not in use. IC4B forms
a simple 2 band equaliser for the left signal which is then sent
to the fader and buffered by IC6B on its return. A feed of the
pre-fade signal is sent to IC18, an SSM2402. The left and right
pre fader signals both use this chip as a mute IC. The left and
right signals are also combined to give a mono pre fader signal.
From the fader buffers the left and right signals both go through
IC17, again an SSM2402, which cuts the post fader effect return
signals. A pan stage follows and from here the signals can be
routed to the various buses.
VCA MASTER MODULES