Service manual

4. Mono Input Module.

The input module houses the analogue insert, EQ, VCA, mute, pan and bus feed circuits along

with logic circuits to control routing and other major functions.

Audio signals are received from the input pod via differential amplifier IC9 and fed to the insert

and EQ circuits. The order of these elements is determined by switch SW3. ST1 connects the

input module to the test input bus: this is for factory or service use only and the links should be

set to the normal position at all other times.

The insert send circuit is formed by the differential output amplifier IC10. Output symmetry is

adjusted by pre-set VR1 and high frequency stability into any load is assured by filter capacitors

C46, C47, C48 and C49. Further filtering is achieved by T filters in the console frame and AC

coupling is via C44 and C45.

The insert return circuit is fed via T filters in the frame to the differential amplifier IC11. Pre-set

VR2 provides CMR adjustment and capacitors C52, C53, C54 and C55 provide additional high

frequency filtering; C56 and C57 provide AC coupling.

The EQ is a 4 band full parametric type for which all the active circuits are housed on two ce-

ramic hybrids HD1 and HD2. High performance is achieved by use of laser trimmed precision

resistors and surface mount components. HD1 has the treble and hi mid equaliser, and HD2 has

the lo mid and bass.

Insert and EQ in/out switching is performed by FETs Q1, Q2, Q3 and Q4 in conjunction with

amplifiers IC12 and IC13. The FETs are controlled from the automation system via shift register

IC31 and CMOS switch IC14.

After the insert and EQ the audio signal is buffered by amplifier IC15 and split to fed both pre

fade mute and VCA circuits. The VCA IC16 is controlled from the fader via the vca line and

buffer amplifier IC19. Pre-set VR4 sets the nominal VCA gain to +10dB and VR3 trims the

distortion to a minimum.

FETs Q5, Q6, Q7 and Q8 create the mute circuit in conjunction with amplifier IC17. Control of

the mute and mute indicator is achieved via invertor IC20 and triple input AND gate IC21. The

indicator will illuminate at half brightness if the solo in place is active and the solo line is not, if

the mute all is active or if the mute line is active. If a link is fitted at ST2 the indicator will illumi-

nate at half brightness when the VCA gain falls below -70dB. A comparitor IC19 monitors the

vca line for this function which can also be used to drive a fader start relay RLA1 as an option.

When the mute switch SW6 is pressed it triggers a bi-stable flip flop formed by IC20. When this

bi-stable activates the mute or the automation recalls a mute via the mute auto and R146 the

indicator will illuminate at full brightness.

The direct output can be sourced post fade, pre fade or pre insert and EQ. Switches SW4 and

SW5 make this selection and the output level is then adjusted by potentiometer RV13 before

being amplified by IC18.

Pre and post VCA signals are fed to the pan circuits formed by potentiometer RV14 (+RV114)

and amplifiers IC22 and IC25. Six summing buffers formed by IC23, IC24 and IC26 are used to

drive 42 of the modules bus sends. Transistors Q12, Q13, Q14, Q15, Q16, Q17, Q20 and Q21