Service manual

The insert return circuits are fed via T filters in the frame to differential amplifiers IC3 and IC5.

Pre-sets VR2 and VR7 provides CMR adjustment and capacitors C9, C10, C11, C12, C23, C24,

C25 and C26 provide additional high frequency filtering; C13, C14, C27 and C28 provide AC

coupling.

The EQ is 4 band with full parametric mid frequencies for which all the active circuits are housed

on a removable sub board. The treble and bass circuits are formed around invertor amplifiers IC11

and IC 17. Potentiometers RV1 and RV10 adjust the level and phase of the signals that are feed

back to the non inverting inputs of IC11 and IC17. This controls the boost and cut of the filters.

The feed back is fed via frequency adjustable second order (hi and lo pass) filters which are

formed by amplifiers IC12 and part of IC17. Frequency adjustment of these filters is achieved via

potentiometers RV3 and RV12. The mid frequency circuits are created in a similar way using

invertor amplifiers IC13, IC14, IC15 and IC16 but utilising the band pass output from state

variable filters to provide the frequency and bandwidth adjustment. Potentiometers RV4 and RV5

provide the filter boost and cut adjustment whilst RV6 and RV9 adjust the frequency.

Potentiometers RV5 and RV8 adjust the relative levels of the two feed back paths within the state

variable filters so as to adjust the band width of the EQ.

Insert and EQ in/out switching is performed by CMOS switches IC6 and IC18. These are control-

led from the automation system via shift register IC31 and transistors Q1 and Q2.

Direct output feeds to the stereo pod are provided post insert and EQ but they can be selected to

be pre insert and EQ by links on the pod module.

After the insert and EQ the audio signals are fed to FETs Q5, Q6, Q7 and Q8 which create the

pre fade mute circuits in conjunction with amplifier IC7. 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 illuminate 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 bright-

ness.

The post mute signals feed the VCA circuits formed by amplifier IC10 and VCAs IC8 and IC9.

The VCAs are controlled from the fader via the vca line and buffer amplifier IC19. Pre-set VR4

sets the nominal VCA gains to +10dB whilst VR3 and VR8 trim the distortion levels to a mini-

mum. FETs Q36 and Q37 create post VCA attenuators that ensure maximum cut off when the

fader down or the channel is muted. These are controlled like the mute FETs from triple input

AND gate IC21.

Pre and post VCA signals are fed to the pan circuits formed by potentiometer RV13, RV14 and

summing buffers IC23 and IC26. The buffers drive the 16 groups, 8 stereo auxes and the 2 solo

busses. Transistors Q16, Q17, Q20 and Q21 are used to increase current drive capabilities when

required. A further summing buffer IC24 is used with transistors Q12, Q13, Q14 and Q15 to

provide pre and post fader summed mono signals to drive the 16 mono aux busses. Crosstalk and

noise are kept to a minimum within the module and the console bus system by use of an active

ground reference system. A clean 0VA or noise reference is sent from the master module to all

the input modules. This is buffered by IC27 which provides the active ground reference which is