31
low charge held on C155; once this capacitor has charged to a logic high the solo can be cleared
by the solo clear bus via section C of IC26. If the solo switch is held down capacitor C151 dis-
charges and resets the flip flop; the solo is now held on by diode D90 until the switch is released.
The group signal can also be soloed as part of a vca solo group; this is selectable via SW30 to
SW31.
8. Master Module.
The master module controls the 3 main outputs and incorporates inserts, solo in place functions as
well as additional record outputs and meters.
The master summing amplifiers IC2 and IC4 are used to recover voltage from the master left and
right busses and from the master aux left and right busses via FETs Q1 and Q2. The aux inputs
can be muted by switch SW1 which controls the FETs and also activates mutes on the group
module via the mute aux control line. The master module provides a clean 0VA or noise refer-
ence which is sent to all the input and group modules to minimise crosstalk and mains born inter-
ference. This is also used as a reference for the summing amplifiers; capacitors C7 and C16 pro-
vide AC coupling and capacitor/resistor networks C8, C17, R12 and R32 ensure maximum stabil-
ity and high frequency rejection at all gains.
A pan balance control is formed by potentiometer RV1 and the second halves of amplifiers IC2
and IC4. The output from the pan buffer is summed with the bus inject signals at IC5 and IC6 to
provide left, right and mono signals. Note that the pan control only acts on the bus signals not the
bus inject.
Bus inject signals are fed via T filters in the frame to differential amplifiers IC1 and IC3. Pre-set
VR1 and VR2 provide CMR adjustment and capacitors C1, C2, C3, C4, C10, C11, C12 and C13
provide additional high frequency filtering; C5, C6, C14 and C15 provide AC coupling.
The left, right and mono signals pass to the insert points via CMOS switches IC7 and IC8 which
select either master or solo signals depending on the solo in place status. The insert send circuits
are formed by differential output amplifiers IC11, IC13 and IC15. Output symmetry is adjusted by
pre-sets VR3, VR5 and VR7 while high frequency stability into any load is assured by filter
capacitors C34, C35, C36, C37, C49, C50, C51, C52, C64, C65, C65 and C67. Further filtering
is achieved by T filters in the console frame and AC coupling is via C38, C39, C53, C54, C68 and
C69.
The insert return circuits are fed via T filters in the frame to the differential amplifiers IC12, IC14
and IC16. Pre-sets VR4, VR6 and VR8 provides CMR adjustment and capacitors C40, C41, C42,
C43, C55, C56, C57, C58, C70, C71, C72 and C73 provide additional high frequency filtering;
C44, C45, C59, C60, C74 and C75 provide AC coupling. The inserts are selected in or out by
switches SW2, SW3 and SW4.
Post insert signals are fed to the VCAs which adjust the signal level and perform signal mutes via
control from faders RV2, RV3, CMOS switch IC25 and amplifiers IC24 and IC26. Pre-set VR15
sets the nominal VCA gain to +10dB and VR9, VR11 and VR13 trim the distortion to a mini-
mum.
The VCA outputs connect to differential output amplifiers IC19, IC21 and IC23. Output symme-
try is adjusted by pre-sets VR10, VR12 and VR14 while high frequency stability into any load is
assured by filter capacitors C82, C83, C84, C85, C93, C94, C95, C96, C104, C105, C106 and
Summary of Contents for XL4
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