TL AUDIO M4 TUBE CONSOLE

USER MANUAL

TL AUDIO M4

TUBE CONSOLE
M4 INTRODUCTION..... 3 M4 MIXER TECHNICAL SPECIFICATION.... 4 Mic Input:..... 4 Line Input:..... 4 Phase Rev:..... 4 High Pass Filter:..... 4 Frequency Response:.... 4 Distortion:..... 4 Noise:...... 4 EQ:..... 4 Insert Point:...... 4 Track Output:..... 4 Fader:..... 5 L+R Outputs:..... 5 Aux Sends:..... 5 Talkback:..... 5 Stereo Returns:.... 5 Monitoring:..... 5 Power Supply:..... 5 Digital I/O:..... 6 Dimensions:...... 6 M4 MIXER OPERATION..... 7 Phase Reverse..... 8 Insertion Points.... 9 Aux Sends..... 9 Track Level Control..... 9 Pan Control..... 10 Mute Switch..... 10 Aux Masters..... 11 Monitor and Headphone Level.... 11 PFL Balance Level..... 11

M4 Introduction

The M4 is the perfect solution for the modern day studio. Anyone who has used or heard our outboard equipment, will be familiar with its ability to create a warm, smooth, and clean sound that can inject wonderful feel into your recordings. Our acclaimed VTC console has also now been accepted as a great sounding must have in the professional recording environment, with many high profile users. The M4 offers you the quality of our outboard, in a desk that is more compact and affordable than the VTC but still offers you the same great sound. It has been designed to maximise todays recording techniques, with the addition of an optional ADAT output for easy digital connection to your recording device and software. It makes the perfect front end to any digital recording set up, taking away that clinical, sterile sound whilst adding warmth and depth to your recordings giving you the sound that you have been longing for. Everything about the M4 has been designed to give you maximum pleasure, from the unbelievably great sounding 4 band sweepable EQ section, to the numerous valve stages and digital output options. You can be sure that the desk is not only a fantastic piece of engineering, it is also great eye candy! Available in 16, 24 and 32 channel options the M4 combines that classic valve sound with modern functionality.

M4 User Manual

M4 MIXER TECHNICAL SPECIFICATION.

Mic Input:

Balanced XLR socket with switchable 48V phantom power, Gain range +16dB to +60dB with 30dB pad, Frequency response +0, -2dB, 20Hz to 40KHz (at 40dB gain), Input noise (EIN) -127dBu (150 ohm source, 22Hz to 22KHz), Switchable +48V Phantom Power. Balanced TRS jack socket, Input impedance 22Kohm, Gain range -20dB to +20dB, Maximum input level +26dBu. Applies to Mic and Line inputs.

Line Input:

Phase Rev:
High Pass Filter: -3dB @ 90Hz, second order. Applies to Mic and Line inputs. Frequency Response: (Line Input to Track Output) +0, -0.5dB, 10Hz to

40KHz.

Distortion: Noise:
0.4% typical (see note). -85dBu, 22Hz to 22KHz, (Line Input to Track Output, Input gain and Track level @
4 Band, with shelving LF/HF and peaking LM/HM, EQ On switch and LED, HF +/-15dB @ 10KHz, HM +/-15dB @ 500Hz to 18KHz, LM +/-15dB @ 50Hz to 2KHz, LF +/-15dB @ 100Hz. Balanced send and return on TRS jacks, Nominal level switchable to +4dBu or -10dBu, Insert On switch and LED. Insert Pre (EQ) switch. Channel direct out, independent of mute switch and Track Pre EQ switch,

Insert Point:

Track Output:

fader,

Level trim +/-15dB, Nominal level switchable to +4dBu or -10dBu, Noise -85dBu / -97dBu (+4dBu / -10dBu nominal), Maximum level +22dBu / +12dBu (+4dBu / -10dBu nominal), Balanced output on TRS jack.

Fader:

+12dBu
100mm K Series, Mute and PFL switches and LEDs, Routing to L+R busses via Pan control, Drive LED with illumination increasing from +4dBu to indicating valve signal level, Peak LED illuminating @ +19dBu, monitoring channel input amplifier and post fader signal. Balanced mix busses, Balanced insertion points with +4dBu / -10dBu switch, Separate L and R master faders, Output via balanced XLR connectors, Noise -72dBu, Maximum level +26dBu. Aux 1 and 2 switchable Pre fader, Aux 3 and 4 post fader, Channel send level controls plus master level with PFL switch, Balanced outputs with +4dBu / -10dBu switches. XLR socket for mic with level control, Switches with LEDs to route to Aux 1 and Aux 2.

L+R Outputs:

Aux Sends:

Talkback:

Stereo Returns: Two, balanced stereo returns with +4dBu / -10dBu switches,
Level and balance controls and PFL switches with LEDs.

Monitoring:

Balanced outputs on TRS jacks, High quality level control with 29mm knob, PFL relative level trim control with +/-20dB range, Switch with LED to select balanced 2 Track return, LS mute switch with LED, Headphone output with independent level control, Twin illuminated 45mm VU meters with Peak LEDs, Front panel accessable 0VU trims. External 2U rack mounting supply, 2 metre cable attached to desk with plug and socket on PSU, PSU switchable for 110-220V 60Hz or 220-240V 50Hz use, Typical power consumption 200VA (16 channel), 250VA (24 channel), 300VA (32 channel).

Power Supply:

Digital I/O:

module

Optional digital ouput module for L+R outputs, and I/O for each group of 8 channels. Outputs follow Track outputs, inputs normalled to analogue Line inputs. Please see separate sheets for digital specifications. All consoles are 815mm (32) deep, plus at least at rear of console for PSU and audio connections, All consoles are 222mm (8.75) high. Length of 16 channel console 694mm (27.3), Length of 24 channel console 950mm (37.4), Length of 32 channel console 1206mm (47.5). (Dimensions include wood trim).

Dimensions:

100mm (4)

Note: 0dB

Distortion measured Line Input to Track Output at +4dBu input and
gain over a bandwidth of 20Hz to 20KHz. The distortion is predominately tube generated second harmonic. Increasing the Drive level by applying more input gain progressively increases the distortion. The above figures are representative of typical production consoles, but are not guaranteed limits for any particular console. These specifications are subject to change without notice.

M4 MIXER OPERATION

Input Selection
You must ensure that the correct input connector, mic or line, is being used from the required source. You can select the type of input by pressing the 'LINE' switch at the top right of each channel strip in or out. In the "up' position the mic input is selected; depressing the 'LINE' switch selects the line input as the source. Note that you can have mic and line inputs connected at the same time but will only be able to select a single input at a time.

Input Gain Control

The gain control should be set to obtain the best signal to noise ratio, whilst preserving adequate headroom. Any changes in gain level should be gradual to avoid sudden overload or severe distortion. Extra care should be taken with higher level inputs, and high gain settings should be used sparingly to avoid an increase in the noise floor and the introduction of distortion.

Line Input

A typical line input will require less gain than a microphone signal as it is a 'hotter' source. You should have the gain set to a minimum when connecting a line input, then gradually increase it to achieve the required level.

Microphone Input

When connecting a microphone to the M4, start with the gain set to a minimum value and gradually increase until the sound source is just tickling 0dB on the meters when the source sound is at average output level. You can than choose how much you would like to drive the valves to produce the required sound. If Phantom power is needed, activate it before setting the gain by depressing the button marked '48V' at the back of the channel strip. Although the M4 provides 48V of phantom power, microphones requiring less than 48V can still be connected without any difficulties. CAUTION: Operation of the phantom power switch, or plugging a microphone in with the phantom power applied, may cause an audible click or thump in your loudspeakers. To avoid this happening, ensure that the channel fader and stereo master faders are set to a minimum before operating the switch or plugging in a microphone. Switching between mic and line with high input gain settings may also cause an audible thump if the level control is not turned down.

Phase Reverse

The phase reverse switch, located to the bottom left of the gain control and labeled 'PHASE', is used to invert the phase of the input signal. It is active on both mic and line inputs. This function could be required when processing a signal that is out of phase with other signals in a mix, in which case the resultant phase error typically appears as a loss of low frequency content, due to cancellation of out of phase components. Phase reverse is commonly used when recording the bottom of a snare drum (if also using a mic on top of the snare), the back of a guitar cab (if also recording signal from the front of the cab), and when performing the stereo recording technique known as an MS pair.

High Pass Filter

This low cut filter provides 12dB per octave of gain reduction with the -3dB point being at 90Hz. Like the phase reverse switch, the high pass filter is active on both mic and line inputs, and is ideal for removing low frequency rumble. The filter can be useful in restricting 'popping' on vocals or even low frequencies caused by contact with microphone stands or microphone cables. Popping is an undesirable thump that is caused by close-miking certain spoken or sung letters, namely 'P' or 'B'. These particular letters cause a sudden expulsion of air that can result in an audible thump. As this thump has a lot of low frequency content the high pass filter can help to reduce the problem, as can using a pop filter (a device usually made out of nylon material similar to stockings) suspended in front of the microphone. The low cut filter is easily bypassed for quick A/B comparison.

30dB Pad

Occasionally when using sensitive condenser microphones the source signal may be too loud for the input preamp. In this situation, to avoid any overloading or distortion of the mic preamp stage, the 30dB pad can be used to reduce the input gain to a more manageable level. The 30dB pad only applies to the microphone input.

Equalisation

Before switching the EQ into circuit, it is advisable to set the cut/boost controls to their centre, or flat, position. The EQ is brought into circuit with the 'EQ' push switch, signalled by a green LED. Each channel has four bands of equalisation: shelving low frequency (LF) (i.e. it extends from the selected frequency to the extreme low frequency limit of the equaliser's response.), peaking sweepable
low-mid (LM) (i.e. it boosts or cuts a section of the audio spectrum around its selected centre frequency only.), peaking, sweepable high-mid (HM) and shelving high frequency (HF). The LF shelf operates at a frequency of 80Hz, while the HF shelf is set at 12kHz. The EQ slopes have a second order 12dB/octave response, and an associated gain control on both bands provides up to 15dB of cut or boost on each selected frequency, controlling the full range of frequencies below the LF corner frequency and above the HF corner frequency. Both mid bands have a fixed Q of 0.7 (which corresponds to a bandwidth of around 1.5 octaves) allowing +/- 15dB cut or boost over a moderately broad band of frequencies. The centre frequency is selected via the dedicated variable frequency control, and the required amount of cut or boost is applied using the associated gain control. The range of frequencies selectable is 50Hz to 2kHz on the LM band, and 500Hz to 18kHz on the HM band, giving a wide spread of frequencies with good overlap in the 500Hz to 2kHz region. You should frequently A/B the sound you are Equalising by pressing and depressing the EQ button, it is astonishing how quickly the ear can adjust to changes. By making frequent comparisons you can make sure you do not stray from the required sound. It is also worth spending some time getting used to the EQ on the M4 - it sounds great and you'll be amazed how versatile and musical it can be.

Insertion Points

Although the insert points are configured to be pre EQ, you can make them post EQ by depressing the button marked 'POST' in the insert section (under the EQ section on each channel strip). There is also a button to enable and disable the insert within the signal chain, this allows for easy A/B comparison of the signal and is also great for live set ups and recording when you want to quickly disable an insert (i.e. a gate).

Aux Sends

Each channel strip has 4 auxiliary sends, two of which can be set to pre fade send. Pre fade sends would typically be used for creating headphone cues, whilst post fade sends are used for effects sends (i.e. reverb, etc). Aux 1 and Aux 2 are switchable to pre, Aux 3 and Aux 4 are permanently fixed to post fade.

Track Level Control

This control sets the level of the signal being sent via the direct outputs, in enables you to create a different mix to tape than what is being heard through the main stereo bus from the channel faders - ideal for live situations. The direct output is also selectable to become Pre EQ by pressing the button located to the bottom right of the track level knob. If you want the level to tape to be the same value as the fader then leave the knob in the central position, set to 0dB.

Pan Control

The pan control positions the image within the stereo field, from fully left in the anticlockwise position, through centre at the dented position to fully right in the clockwise position. The gain law is -3dB at the centre.

Mute Switch

The channel may be muted or switched on without affecting the level set on the channel fader. Red LED indicators show which channels are currently muted.

PFL Switch

When PFL (Pre Fade Listen) is activated a yellow LED illuminates above the button on the channel strip and also in the master section. PFL allows you to monitor the incoming source before it reaches the channel fader and the signal is sent to the main output. It is normal to use PFL when setting the gain level for an incoming source.

Channel Fader

A 100mm fader is located at the bottom of the channel, and sets the level of the channel's signal being fed to the stereo mix bus. The fader provides up to 10dB of gain at its highest point.

Drive and Peak LEDs

The yellow Drive LED provides a visual indication of the signal level through the input valve stage, and therefore the extent of 'warming' or valve character being introduced. The drive LED will gradually illuminate as the input level or gain is increased, over the range +6dBu to +16dBu. The red Peak LED operates as a conventional warning that clipping is about to occur. The operating level of both input and post fader stages is monitored, and the LED illuminates at a threshold of +21dBu, when there is less than 5dB of headroom remaining to the direct output. Normal operation would be to set the input gain so that the Drive LED is illuminating regularly, with occasional illumination of the Peak LED occurring on loud transients.

Stereo Mix

Two 100mm faders control the stereo mix output level.

Aux Masters

Each aux send features a rotary master level control, which governs the overall level from the aux output. An associated PFL switch allows each aux send to be auditioned in isolation, by placing the aux signal (pre the master level control) on the PFL buss. An operating level switch is provided adjacent to the rear panel connector which selects whether each aux send functions at -10dB or +4dB, allowing easy interfacing with all types of equipment.

Effects Returns

The two stereo effects returns are each equipped with a rotary fader and a L/R balance control. Both returns are fed directly into the stereo mix. A PFL switch allows each return to be auditioned in isolation. A mono signal can be fed to either of the returns by connecting it to the left hand return input only. This will automatically feed the mono signal equally to both left and right hand sides of the stereo buss simultaneously. An operating level switch is provided adjacent to the rear panel connector which selects whether each aux return functions at -10dB or +4dB, allowing easy interfacing with all types of equipment. The effects returns are typically used to feed the outputs of FX devices back into the stereo mix, adding 'wet' signal to the 'dry' stereo mix. However, the returns can also be used as simple extra line inputs for signals that require no EQ or FX to be added to them via the mixer.
Monitor and Headphone Level
The M4 provides a stereo monitor output, for connection to a power amplifier and monitor loudspeakers, plus a front panel headphone output. The Monitor level control governs the level of signal fed to both these outputs. The monitor signal normally follows the main stereo output, but will automatically switch over to the PFL buss whenever any PFL button is pressed, this condition being indicated by a yellow LED. Similarly, the monitor signal will follow the 2T return when the 2T return switch is activated in the master section.

PFL Balance Level

The PFL Balance control allows adjustment of the PFL signal level relative to the main stereo monitor level, as the PFL signal could be considerably louder than the stereo output - depending on the mix and sound source.

2-Track Return

When recording the stereo mix output onto DAT or CD-R, for example, it is sometimes useful to be able to monitor the output from the mastering machine, in place of the mixer stereo output, as confirmation that the signal is actually being recorded (this is particularly useful when using a four headed DAT machine or a three -headed analogue 2T machine, since the off-tape signal can be monitored). This is achieved by selecting the 2T Return switch near the monitor level control. This facility may also be used for playback after recording.

Loudspeaker Mute

This switch mutes the rear panel monitor output. This is particularly useful when using headphones, enabling the main monitors to be muted without needing to turn off their amplifiers. This is also useful for temporarily muting the monitors without needing to alter any fader levels, for instance during a telephone call.

Metering

Two illuminated VU meters on the M4 will normally monitor the main stereo output, but automatically switch to monitor the PFL buss when any PFL switch is engaged. Similarly, when the 2T return is selected as the monitor source (via the relevant select switch - see section 4.22) the meters will automatically switch to monitor the 2T return. The meters are calibrated to indicate 0VU when a signal level of +4dBu is generated at the main outputs. A pair of red Peak LEDs operate on the stereo buss as a conventional warning that clipping is about to occur. The LEDs illuminate at a threshold of +21dBu, when there is less than 5dB of headroom remaining on the main outputs. Normal operation would be to set the stereo buss fader levels so that occasional illumination of the Peak LEDs occurs on loud transients.

Digital Output Option

The optional DO8 card can be fitted to the back of the M4 and each card provides 8 channels over ADAT lightpipe. This professional protocol makes for easy connection when conducting computer based recording, and makes the M4 the perfect front-end solution for digital recording set ups. There is also the optional DO2 card that fits into the back of the master section of the M4 and provides stereo digital output in SPDIF format (RCA Phono connectors). The DO2 is has a fixed 24 bit word length, but the sample rate is switchable between 44.1, 48, 88.2 and 96 kHz. These are selectable from the back of the digital card.

Wordclock Input

A rear panel input (on the back of the DO2 & DO8 card) is provided for connecting the M4 to an external master clock source. The wordclock input connector is a BNC-type terminated in 75 ohms.
A FINAL WORD We hope you will enjoy your new M4 console, we're confident that once you start using it you'll wonder how you managed without one! For best results, switch your M4 console on 30 minutes before the start of your session to allow the tubes to fully warm up. Enjoy!

2.10 Aux Outputs. The Aux outputs are provided on unbalanced, 2 pin jack connectors. The mating connectors should be wired as follows: - Sleeve = Ground (screen), - Tip = Signal Phase (+ or hot).
2.11 Aux Returns. Six stereo inputs are provided, for effects returns or other line level sources. The connectors are 3 pin jack sockets, and the mating connectors should be wired as follows: - Sleeve = Ground (screen), - Tip - Ring = Signal Phase (+ or hot), = Signal Non-Phase (- or cold).
If unbalanced signals are used, the screen and ring should both be connected to ground. The aux returns are normalled so that if a mono signal is connected to the left input only, this signal is fed equally to left and right return paths: thus enabling easy connection of mono effects devices or line sources. 2.12 Main Stereo Output. The main outputs are via balanced, 3 pin male XLR connectors operating at +4dBu. The mating connectors should be wired as follows: - Pin 1 = Ground (screen), - Pin 2 = Signal Phase (+ or hot), - Pin 3 = Signal Non-Phase (- or cold). If an unbalanced output is required, pins 1 and 3 should both be connected to ground. 2.13 Unbalanced Stereo Output. The main stereo output is also duplicated on unbalanced mono jack connectors operating at 10dBu. The mating connector should be wired as follows: - Sleeve = Ground (screen), - Tip = Signal Phase (+ or hot).
2.14 Master Insertion Points. The master insertion points are interfaced via a 3 pin, 0.25 switched jack socket on the rear of the unit. The pin connections are: - Sleeve = Ground, - Tip = Send, - Ring = Return. The insertion point is unbalanced. If used as an additional send only (e.g. as a send to a tape machine or monitor mixing desk), the Tip and Ring should be wired together, to preserve the signal path through the insertion point. The master insertion point is active on both the balanced and unbalanced stereo outputs. 2.15 Mix B Output. The Mix B outputs are via balanced, 3 pin jack connectors. The mating connectors should be wired as follows: Balanced outputs: - Tip = Signal Phase (+ or hot), - Ring = Signal Non-Phase (- or cold), - Screen = Ground. If unbalanced signals are used, the screen and ring should both be connected to ground. 2.16 Control Room , Studio and Alternate L/S Outputs. All three of these monitor outputs are via balanced, 3 pin jack connectors. The mating connectors should be wired as follows: - Sleeve = Ground (screen), - Tip - Ring = Signal Phase (+ or hot), = Signal Non-Phase (- or cold).
If an unbalanced output is required, the screen and ring should both be connected to ground. 2.17 Stereo 2T Returns (2TA and 2TB).

PK SIG SOLO

+10 +5 STAT
AUX SEND MUTING (11) Each send can be completely muted by individual on/off switches: thus preventing any low level bleed-through of effects and allowing an instant comparison of dry and processed signals.

3.5 Equalisation Section

The VTC has been praised for its classic, musical sounding EQ, capable of overall contouring, creative shaping and corrective treatments. The EQ stage shares the warmth, transparency and smoothness of the TL Audios outboard EQ units. The four band EQ comprises three sections, all within easy reach of the engineer: High Mid Parametric, Low Mid Parametric and HF/ LF Shelving. In addition, part or all of the EQ is assignable to the main channel or tape monitor signal paths making it a very practical and flexible tool. The EQ stage is post valve stage/insert point, and pre fader.
HIGH MID PARAMETRIC EQ (12)
H-MID +/-15 2K 500 +15 5K Hz
Three pots control Parametric Cut/ Boost: +/-15dB Centre Frequency: 500Hz - 18kHz Q: Variable from 0.8 - 7.0 (1.25 - 0.15 octaves)

the action section:

When the Q control is turned fully clockwise to its minimum value the filters notch is wide. At this setting it will have an effect on a wider range of frequencies, thus providing a more broadband and musical effect. When turned fully anti-clockwise the notch of the filter is narrow and so a more limited frequency range is affected. This setting provides a more severe, corrective EQ action.
LOW MID PARAMETRIC EQ (13)

L-MID +/-+Hz 2K Q

Cut/Boost C e n t r e 2kHz Q octaves)

Frequency

+/-15dB 50Hz 0.8 - 7.0 (1.25 - 0.15
LM Parametric EQ works in the same way as the HM band. Note the wide overlap of the two bands in the centre frequency range of 500Hz 2kHz, making the parametric section very useful for creative and corrective manipulation of the many sound sources with energy in the mid frequency band. The lower frequency area of this parametric also substantially overlaps with the LF shelving control, allowing even greater control of low frequency, bass end material. EQ ON (14)
The EQ switch found at the base of the lower mid parametric section switches the EQ ON for the main channel signal path only. When the indicator LED is lit, the equaliser is active. Dedicated switches are used to apply EQ to the monitor signal path (see Section 3.6). HF and LF SHELVING (15) T h e Baxendale shelving filters operate 15 at: H F 12kHz (12dB/ octave) LF 80Hz (12dB/octave) Cut/Boost +/- 15dB HF and LF shelving is normally in the main channel path but can be switched to Mix B (see Section 3.6).

HF -15 +15 LF -15 +15

3.6 Mix B Monitor Section

PAN (16)

PAN MIX B
The Monitor section is labelled Mix B and 16 comprises a Pan pot , Mute switch, Signal Present and Peak LEDs, a Solo LED, 17 EQ assign switches, Source, Auto and Status switching, and a high quality 60mm Alps fader. The Mix B signals are all mixed and fed to a separate pair of outputs in the Master Section and can be 26 also be routed to the Stereo Mix, Control Room, Studio or Headphones outputs.

L R MUTE PK SIG

dB STAT

+10 +-5 -10

AUTO SRCE-CH E Q

-20 -30 -40 -50 -80

HM/LM EQ
A dedicated pan pot with centre detent controls the stereo imaging of signals in the Mix B signal path.

ROUTING

There is no individual multitrack tape routing system for the Mix B channels, since the group routing switches are not accessible from the Mix B section. However, a completely separate mix can be processed via the Mix B faders and fed to a recorder via the consoles dedicated Mix B stereo outputs in the master section. MUTE (17) The large illuminating mute switch can be activated manually to cut the signal on its monitor channel. It will also illuminate and mute the signal for that channel if the SOLO IN PLACE function is activated elsewhere on the console.
PEAK (18) The peak indicator starts to illuminate when the signal is about to overload the monitor channel input stage. In the absence of channel meters (which can be purchased as an optional extra) the peak indicator is a useful, quick guide to signal level.
In practice the red peak light is activated at a level of +18dB or above, allowing some advance warning when bringing up the monitor input gain before the headroom limit of +26dB is reached.

SIGNAL PRESENT (19)

This is a green LED which illuminates to show that a signal is present on the monitor channel path when it reaches a level of -30dB.
SOLO (20) The solo button is found at the top of the function button array and in its default mode acts as a mono PFL (pre fade listen). When the SOLO IN PLACE function is activated on the Master Section, the monitor channel solo button will activate the solo in place function instead of PFL. In the latter mode the monitor channel solo button is linked to both main channel and monitor channel mute status indicators. SOURCE-CHANNEL (SRCE-CH) (21) Routes the channel signal to the monitor, in place of the tape return signal. Note that this is different from the Flip switch which reverses channel and tape return signals. In practice the Source-Channel button may be used to set up two separate mixes running side by side - one on the main channel faders and another on the Mix B faders. This can be useful for purposes of comparison or later editing of separate mixes. HF/ LF EQ (22) This button assigns the channel high and low frequency EQ filters to the Mix B section signal path. LM/HM EQ (23) This switch reassigns the channel parametric mid EQ filters to the Mix B signal path. Note: Both the above are dedicated monitor channel EQ status switches and independent of the main channel EQ On status switch. In practice this means that even when the EQ switch located on the main channel is in the off position, EQ is still available for the monitor section should the assign buttons be activated.

SOLO (31)

Each channel solo switch activates PFL or SOLO IN PLACE mode (see Master Section for details of these two modes of operation, plus AFL which applies to certain master section signals). In its default mode the solo switch will activate PFL mode (pre fade listen). In this mode, the solod signal is fed to a separate PFL stereo mix buss, which replaces the normal Control Room output signal of the desk. All other outputs from the console remain unchanged in this mode, so signals from the Left/Right outputs to a master recorder (for example) will not be disrupted. The PFL signal is mono in the sense that the solod signal is fed equally to both left and right outputs, and is pre the channel pan control. PFL/AFL active is signalled by a red LED adjacent to the active switch and by a yellow LED on the Master Module VU meter panel.
However, if SOLO IN PLACE is activated on the Master Section, the solo button will not function as a PFL, but as a Solo In Place. In this mode any channel on which the solo switch is activated will cause all the other channels and Mix B paths to be muted. Note that this will affect outputs to the recorder so programme material may be lost if care is not taken. AUTO and STATUS (32) If automation is fitted the Auto switch allows a channels automation stage to be bypassed and the Status switch acts as a local status on/off switch (see 24 and 25). BUSS (33)
Each channels individual tape output (a balanced quarter inch jack socket on the rear connector panel) works by default as a direct post fader output to the recorder, with desk channels 1 - 24 feeding recorder inputs 1 - 24, for instance. However, when the Buss button is selected on any channel, the tape output of that channel is fed from the output of one of the relevant group faders. And this relationship between group outputs and channels is defined in groups of eight: Group 1 signal will appear at tape outputs of channels 1, 9, 17 etc. Group 2 signal will appear at tape outputs of channels 2, 10, 18 etc. and so on for groups 3 to 8. (This will not affect the signal running through either the main channel or Mix B stage of that particular desk channel. Only the tape output is connected to the group fader signal.) In effect the group becomes normalised to the tape outputs in a system providing maximum flexibility for an eight group console. This enables all the tracks on a multitrack tape machine to be accessed via the VTCs
channel tape outputs without any need for re-patching. ROUTING BUTTONS (34) As previously mentioned (in 27) the pan pot acts as an odd/even signal feed for the routing matrix. On selection of one of the group routing buttons 1-2, 3-4, 5-6, 7-8, the post fade signal will be sent if panned left to the odd number selected and if panned right - to the even number of your choice. Selection of the L/R buss switch will route the post fade signal to the main mix buss. MAIN CHANNEL FADER (35)

The Mute button cuts the Stereo Return signal path but is not automatically muted when the SIP function is in operation. This allows the engineer to listen to Channel and Mix B sound sources and their effects by simply selecting a solo button on the input channel. Note that none of the Stereo Returns will be automatically muted while in SIP mode, but if the engineer wishes to monitor a source sound on the input channel with a single effect, a combination of SIP and AFL is possible. For example, a vocal may be solod on one input channel and its reverb signal AFLd on the relevant Stereo Return. HEADPHONE SENDS The post fade signal from the effects returns may be sent to either or both Phones 1 and Phones 2 outputs. Once selected there is an individual gain control on each Stereo Effects return to govern the amount of signal level fed to the Phones section. 4.3 HEADPHONE MATRIX
PHONES 1 & PHONES 2 The VTC offers a very versatile headphone mix section where stereo foldback can be sourced from any or all of these signals: Control Room, Mix B, Aux 3/4, Aux 7/8 and External. The solo button functions as a PFL, and it is assumed that Aux 3/4 and Aux 7/8 will be used for headphone cue mixes as they are the main pre fade sends. In this case Aux 3 and 7 will appear on the left of stereo and Aux 4 and 8 on the right. The headphone mix can be checked in the control room by using the Solo (PFL) on the Phones section. The External input allows reference monitoring for performers from any external source such as a click track, CD or cassette. Other 2-Track sources can be routed to the Phones section by using the Control Room master section to select 2TA or 2TB, and then activating the C/Room switch on Phones 1 and/or Phones 2. The External input, unlike the 2-Track inputs, is normalised for stereo or mono operation should a mono source signal be required (simply plug into the left hand input). It could also be used as an additional headphone mix from sources such as Auxes 1/2 or 5/6 (should the need arise) by patching these sends to the External source input. 4.4 OSCILLATOR
The On switch activates the Oscillator, and a second switch allows you to choose between a 1kHz and 10kHz line-up tone. Signal level from the oscillator is governed by a Level control and the tone is routed to all the groups and the main stereo outputs, pre fader. The tone can then be fed to any or all of channel tape outputs by activating the Buss buttons on the required channels. 4.5 MIX B

2.5 kohms 10kohms minimum 100 ohms 47 ohms +26dBu +20dBu +20dBu +70dB +32dB 20Hz to 20kHz +0, -1dB

-97dBr -89dBr -75dBr

-94dBr -92dBr -75dBr -127dBu
0.02% 0.03% 0.03% -100dB @ 1kHz, -83dB @ 15kHz
Due to a policy of continuous development, the above specifications are subject to change without notice. The figures represent typical values for signal paths stated. E & OE.
2.3 2.4 3. 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4. 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 5. 6.
Valve Replacement. Valve Path Identification. Input Bays. Mechanical Construction. Adding Modules to Sub-fitted Consoles. Input Modules. Replacing Mute Switches. Input Circuit Description. Input Stages. Equaliser. Faders and Routing. Module Fault Finding. Master Section. Mechanical Construction. Master Module Circuit Description. Master L+R Outputs. Group Outputs. Mix B Outputs. Aux Outputs. Stereo Returns. Oscillator. Talkback. Headphones. Solo System. Control Room Output. Studio Output. Logic Control. External Monitor Inputs. Metering. Meter Bridge Option. Calibration Procedure. Signal Flow Diagrams.
1. Power Supply Distribution. 1.1. Mechanical Construction. The VTC console mechanical construction consists of a number of bays, each of which houses 8 input channels, plus a further bay for the Master Section. Each bay operates as a sub-system with its own grounding, PSU Regulators, and balanced audio signal connection between bays. The external PSU provides rectified but unregulated DC which is connected via a heavy duty multicore cable to the console. Inside the console frame, the raw DC is bussed to every bay where it is separately fused and regulated. 1.2. Power Supply Fault Finding.
CAUTION: THE POWER SUPPLY AND CONSOLE CONTAIN HIGH VOLTAGES (UP TO 250V DC) AND HIGH POWER CAPACITY, WITH A RISK OF PERSONAL INJURY AND FIRE. SERVICE SHOULD BE PERFORMED BY COMPETENT QUALIFIED PERSONNEL, IN ACCORDANCE WITH CORRECT ENGINEERING PRACTICE. IF IN ANY DOUBT, REFER SERVICE TO THE RETAILER OR DISTRIBUTOR OF THE CONSOLE. The external power supply contains a transformer with a number of secondary windings. These secondaries are individually fused, rectified and smoothed. The fuse ratings and the power supply rails to which they refer are marked on the chassis adjacent to each fuse. CAUTION: FOR CONTINUED PROTECTION AGAINST FIRE, REPLACE FUSES WITH CORRECT TYPE AND RATING ONLY. DISCONNECT THE POWER SUPPLY FROM THE MAINS BEFORE REPLACING ANY FUSE. Fig. 1 is the view of the power supply connector from the outside, with the multicore cable disconnected. The voltages are approximate values, when operated from 230V AC mains supplies. Note that the 16V heater supply is floating, and cannot be measured with respect to ground. The power supply contains bleed resistors to discharge the capacitors when the console is not connected, but may take several minutes to discharge fully. The power supply should only be operated off load by a qualified technician. Never disconnect or reconnect the multicore cable whilst the power supply is connected to the mains or there is any voltage present on the power supply outputs. The regulator module for each bay is located underneath the valve PCB (PC334), in the rear section of the console. To access the regulator module the top cover should be removed, and PC334 removed by disconnecting the two IDC cables at the front of the board, removing the fixing screws and gently lifting the board upwards. The PSU connector that links PC334 to the regulator module should be disconnected before PC334 is finally lifted clear of the console frame. The regulator module will now be accessible. It consists of PC357 mounted onto an aluminium heatsink. Refer to the circuit diagram CD1357. An 8 way plug and socket (CN3) brings the unregulated DC onto the module, where the various rails are immediately fused and then regulated. Failure of any fuse or regulator will normally affect only its own bay, however the loss of one power rail may cause noise injection onto the busses, so all routing switches in the failed bay must be turned off (or the input modules removed), should the remainder of the console be operated in this condition.

The voltage regulators may be individually adjusted by carefully measuring at the output connectors (CN1 and CN2) or the test points marked on PC357. The voltages should be adjusted to: HT: Phantom Power: V+: V-: H+: +180V +/-1V. +48.0V +/-0.1V. +15.2V +/-0.1V. -15.2V +/-0.1V. +6.2V +/-0.1V.
Note that adjustment of H+ by RV5 will also cause a change in H-, as the supply is centre tapped to 0V by R20 and R21. As the H- rail is bussed through the desk, some interaction of adjustment between bays may occur if re-adjusted in the console. When on load, some regulation of the heater supply may occur. This is acceptable as the valve circuits will continue to operate within their specifications with the heater voltage (H+ to H-) as low as 9V. Complete removal of the regulator modules requires the 4 fixing screws to be removed, CN2 and CN3 to be disconnected and their mating cable assemblies to be carefully fed through the module side cut-out as the module is lifted clear of the console. When re-fitting the regulator module, the cables must be guided back through the module cut-out as it is lowered into the console. Take care to leave the valve IDC cables accessible when re-fitting the module. The regulated DC is taken from the module via CN1 (HT, H+ and H-) to the valve board PC334, and via CN2 (V+, V- and 48V) to the input backplane, PC356. Note that in the Master Section, V+ and V- power from CN2 is taken to PC355, and no connection is made to 48V.
2. Valve PCBs. 2.1. Circuit Overview. The console valves are located on PC334 for the channel bays and PC345 for the Master Section. Refer to CD1334 and CD1345 respectively. Note that the signal paths for the Master Section are marked on PC345 component legend layer, and that 2 valves are intentionally not fitted. Each valve stage consists of one half of an ECC83/12AX7A twin triode operating on an HT voltage of approximately 175V after filtering. A pair of complementary high voltage discrete transistors in the anode circuit act as voltage followers, providing higher current drive and power transfer from the stage. The voltage gain is controlled by local feedback, and is individually trimmed at the NE5532 buffer stage which is inverting for the channel path Insertion Send and Master Section, and noninverting for the Monitor path. Refer to the Calibration Procedure for trimmer adjustment. The HT and heater supplies are linked directly from the Regulator module (PC357), whilst all signal, ground and +/-15V supplies are connected to the valve PCBs via their two IDC cables.
CAUTION: THE REAR SECTION OF THE MODULE AND VALVE PCBs CONTAINS CONSOLE TOP COVERS SHOULD NOT CONNECTED TO THE POWER SUPPLY, TECHNICIAN.
CONSOLE CONTAINING THE REGULATOR HIGH VOLTAGES, UP TO +250V DC. THE BE REMOVED WHILST THE CONSOLE IS EXCEPT FOR SERVICE BY A QUALIFIED

replacement as they age. When replacements do become necessary, they should be obtained from the console supplier. ECC83/12AX7A valves are quite commonly available, but the various manufacturers differ greatly in quality and audio performance, and replacement with the same type as originally supplied with the console will ensure consistency of performance. After replacing a valve, the signal path gain should be checked as described in the Calibration Procedure, but no valve bias or other adjustment is necessary. 2.4. Valve Path Identification. The Master Valve paths are identified along the rear edge of the PCB (see above). The channel valves are in line with their respective input modules, and when viewed from the rear of the console the trimmer for the MONITOR (TAPE) PATH is on the LEFT, and the CHANNEL PATH is on the RIGHT.
3. Input Bays. 3.1. Mechanical Construction. The input modules are carried in a steel cradle which is mounted between the console bulkheads. The cradle provides mounting screw points for the modules, plus two rigid PCB backplanes into which the input modules are plugged. All connections to the input modules are made via a two part DIN41612 connector on each of the backplanes. To remove a module, the large black countersunk screws at the top and bottom of the module should be taken out, after which the module can be simply pulled clear of the console. Note that consoles fitted with third party Automation Systems may be installed with additional flying leads to the module and/or faders, and care must be taken not to damage these leads as the module is withdrawn. Both backplanes are passive, i.e. they contain connections only, with no active circuitry (refer to CD1356 and CD1337). The upper backplane, PC356, (nearest the VU meters) carries the power distribution to the input modules, as well as the inputs and outputs for the module, and balanced Aux busses. The power connection may be checked by removing the middle two modules, and measuring the voltage rails as marked on the rear of CN30. The non-patchbay standard console has a separate 16 way IDC cable for each module, carrying the Line Input, Insertion Send + Return, Monitor (Tape) Input and Direct Output to the small PCB (PC335) onto which are mounted the rear panel jack sockets. These IDC cables are secured in place in the console frame, and terminated onto PC356. Consoles with internal or external patchbays have longer IDC cables, taking the above signals from PC356 either directly to the patchbay PCBs or to multiway connectors. Irrespective of any patchbay, the microphone input for each module is via a rear panel mounted XLR connector with an individual screened cable terminated directly onto PC356, close to the module connector. This ensures minimal PCB track length for the mic signal, to achieve good noise immunity. The lower backplane, PC337, carries the balanced buss signals along with PFL and Solo signals. 3.2. Adding Modules to Sub-fitted Consoles. Each Input Bay is normally fitted with eight input modules, although some consoles may be subfitted with individual module blanks or full bay blank panels. When retrofitting modules to consoles initially supplied part fitted, the new modules can be simply plugged into the backplanes. The valves for the new channels will also need to be fitted to PC334, and the console calibration procedure followed. Note that modules should be dedicated to particular positions in the console. If they are moved to another position, the relevant valve stages should be recalibrated, and the engraved mute buttons exchanged. CAUTION: THE CONSOLE POWER SUPPLY MUST BE SWITCHED OFF BEFORE ANY MODULES OR VALVES ARE PLUGGED IN OR OUT.

apparent on various paths. Two valve positions, along with their associated trimmers and ICs, are intentionally not fitted to PC345. The master front backplane, PC336, is linked to the input bay backplanes, PC337, by short IDC cables carrying the balanced busses. These cables plug into the underside of the PCBs, to avoid fouling the input modules. It is unlikely that these cables will need to be removed, but if it should be necessary, all of the input bay modules should be removed from the console, and the IDC cable disconnected from the socket on the underside of PC337. The backplane can be lifted clear of the bay after removing the six screws which secure it to the cradle. The IDC cable must be fed through the bulkhead, and can then be removed. When refitting the cable, ensure that the plug is fully seated into the socket on the underside of the PCB. The majority of the Master section inputs and outputs are via IDC cables connected to the underside of the upper backplane, PC355. The IDC cables are terminated on the jacksocket connector PCBs on the rear panel, or taken to the patchbay. Note that the IDC cables are held in place with clips on the console frame, and their function identified with labels on the cables themselves and the silk screen of PC355 (e.g. Groups, Inserts). 4.2. Master Module Circuit Description. Refer to the Master module block diagram in the specification section of this manual, the circuit diagrams, and the expanded block diagrams in the following sections. The expanded block diagrams include the locations of the various circuit blocks, and main signal names as used on the circuit diagrams. 4.3. Master L+R Outputs. Refer to the expanded block diagram, fig 3. The L+R mix amplifiers are hybrid designs, using a low noise balanced IC first stage on PC336 followed by a valve stage on PC345. Due to the length of cabling that would otherwise be necessary, a L+R sub-mix is formed on the upper Master section, consisting of the stereo return, MixB to L+R path, talkback and oscillator. The sub-mix is buffered and balanced, and routed via the upper backplane, PC355, into the main mix on PC336 by the signals ANC L and R. The mix busses are connected to the mix amplifiers IC16 and IC17 (see CD1336 sheet 4), via the IDC cables at CN4 and CN5 (from the input modules), CN6 from the group fader modules and CN2 from the ancillary sub-mix. The first stage mix amplifier outputs L VIN and R VIN are routed via CN1 to the valve stages on PC345, from where they are returned on the same connector as L VOUT and R VOUT. These signals are immediately routed out to the insertion points by the signals L SND and R SND, via CN2 and PC355. The insertion returns L RTN and R RTN are routed to the L+R master fader module, PC339, as signals L FDR and R FDR via the Master module IDC cable fitted to CN4. The buffered post fade signals L WPR and R WPR are returned on the same IDC cable to PC336, and thence to the output stages on PC355 as signals L OUT and R OUT. The output stages are shown on CD1355 sheets 2 and 3. There are separate buffered stages for the balanced outputs at a nominal level of +4dBu and the unbalanced outputs at a nominal level of 10dBu. The balanced outputs have a trimmer for balance, RV5 and RV6. The L+R level trimmers are located at the valve stages on PC345 - refer to the calibration procedure for setup instructions. The output level is monitored by the meter controller as signals MTR L and MTR R on PC355.

CD1347. Following the balanced receiver stages IC2A and IC2B, the return is taken to the balance control, RV3, and buffered by IC4A and IC4B. The sensitivity of the returns is +4dBu by default, but may be changed to -10dBu by fitting jumpers J1 and J2. The stereo returns are controlled by a 60mm fader, followed by a +10dB buffer (IC3A and IC3B), and routed to the L+R sub-mix. Additional switches on PC347 also provide AFL monitoring and routing to the headphones. 4.8. Oscillator. The oscillator circuit is contained on PC348. Refer to CD1348 sheet 3. Two oscillators provide 1KHz and 10KHz waveforms. The 1KHz is generated by IC1B, with level trimmed by RV3. Similarly, the 10KHz is generated by IC1A, with level trimmed by RV2. These trimmers are located near the sub-front for PC348, but can be accessed and adjusted by propping open the upper master front panel. The oscillators are routed to the groups and L+R mixes pre-fade by the On switch SW5. The trimmers should be adjusted to give +10dBu at the outputs when the faders are at their 0dB position. There is no provision for trimming the oscillator frequencies. When the oscillator switch is in the Off position, the gain of the IC1A and IC1B stages is reduced by the signals E1,E2,E3 and E4, causing the oscillators to shut down, to eliminate any risk of crosstalk. The oscillators can therefore only be adjusted when SW5 is in the On position. 4.9. Talkback. The talkback mic amplifier and routing is also located on PC348. Refer to CD1348 sheet 4. The input from the microphone is on screened cable, directly from the socket on the lower master module to CN1 on PC348. This connector carries a further connection from the logic controller, PC351, which is the talkback on/off signal derived from the talkback On switch near the microphone. Care must be taken when removing either master module to ensure that this cable is not damaged. The microphone signal is amplified by IC6, with gain controlled by RV8. The amplified signal is only passed to the routing switches if the logic control signal is at 1 (+15V). A logic 0 (0V) will mute the talkback signal. The talkback control logic may be either momentary or latching, depending on jumper configuration on the logic PCB (see below). Talkback can be routed to the groups plus L+R busses, studio and headphones. Both the routing switches and On button must be enabled to route talkback through to the outputs. 4.10. Headphones. There are two similar stereo headphone circuits, located on PC349. Refer to CD1349. Each headphone circuit has five sources selected by the push buttons on PC349. These sources are Control Room, MixB, Aux 3/4, Aux 7/8 and the EXT input. The sources are additive, i.e. more than one source may be selected and they will be mixed together. The mix points PHONES 1L etc. are linked out onto the upper master module inter-connect IDC cable, to enable the headphone sends from the stereo returns to also be added. The Aux 3/4 and 7/8 sources route the odd numbered Aux to the headphone left output, and the even numbered Aux to the right output, to facilitate stereo

switch inner. Failure to ensure correct alignment may result in the switch cap springing off suddenly if the switch is operated quickly. The push buttons are controlled by similar circuits. For example, the Control Room L+R push button, SW2, is debounced by IC1B and toggled by the flip-flop IC2A (see CD1351 sheet 2). The output from IC2A is used to turn on the LED via Q2. The flip-flop array is initialised to a predetermined state at power-on by the RESET signal from IC15A. The toggled signals, CR L+R~, etc are active low (as identified by the label ~), and are gated by IC13C, etc (CD1351 sheet 4) to produce active high signals taken out on CN18 to PC352. The gating at IC13C is determined by the state of signals PFL and STD SOLO i.e. if PFL is active or the studio is soloed, the main Control Room sources are inhibited. Solo In Place or PFL mode is controlled by IC7A (CD1351 sheet 2), generating the signals SOLO MODE, used to disconnect the PFL buss on PC336 (see above) and SOLO EN which is routed out onto the input module backplanes, PC337. Switching the Control Room and metering outputs over to the AFL/PFL buss is controlled by the signals PFL and its compliment PFL~ (CD1351 sheet 4). The gate IC14C activates switch over only if Solo In Place is not selected, using the SOLO signal. PFL SIG and AFL SIG are active high, diode ORed signals, activated from the various solo switches on the console. The Studio source selection operates similarly to the Control Room selection, but with an added logic multiplexer to perform the Studio Follow Control Room function. Follow CR is generated by IC6B (CD1351 sheet 3), and controls the gates IC17A/B, etc. Talkback and Control Room dim are controlled by the signal T/B ON at CN18 pin 12. This signal is either momentary if jumper J2 is fitted (the default setting), or latching if J1 is fitted. T/B ON is also taken from PC351 on a flying wire loomed with the talkback microphone cable to PC348 on the upper Master Module. If talkback does not appear on the outputs but the switch illuminates, check that the talkback destination is selected on the upper Master Module and the output fader is open, and that the flying cable is connected to PC348. The logic power supplies on CD1351 are labelled VL+ and VL-. These voltage rails are derived from the master section +15V and 0V respectively, but are decoupled from the audio circuit supplies by R18, R19 and C28, etc. 4.15. External Monitoring Inputs. The console has three stereo monitoring inputs: 2TA, 2TB and EXT. The inputs are on jack sockets on the rear of the master section (or patchbay), with balanced receiver located on the upper master backplane, PC355 (see CD1355 sheet 5). The two track returns are dedicated stereo inputs, but the EXT input is normalled for stereo or mono operation. Each of the external inputs is set to +4dBu nominal sensitivity by default, but may be changed to 10dBu by fitting jumper links to PC355. These jumpers may be accessed by propping open the upper master module. The links that should be fitted are: 2TA: 2TB: EXT: J3 and J6, J2 and J5, J1 and J4.

The external monitoring inputs are routed off PC355 by the IDC cable at CN7, to the Control Room and Studio module, PC352. 4.16. Metering. The console is fitted as standard with retro-style VU meters for the eight groups plus left and right outputs. Each of these meters also has a peak LED adjacent to it. Control of the meters and LEDs is from PC344, located on the master section rear panel and connected to the backplane, PC355, by an IDC cable. The circuit diagram for the meter controller is CD1334, which shows the meter trims accessible from the rear panel, and the peak detect circuits. There is an overall peak threshold trim, also accessible from the rear panel. The default calibration for the trimmers is 0VU = +4dBu and peak LED threshold = +18dBu. 4.17. Meter Bridge Option. The meter controller, PC344, and rear panel of each input section carry a 25 pin D-type connector for connection of the optional LED bargraph meter bridge. The circuit diagrams for the meter bridge are CD1353 (input sections) and CD1354 (master section). The master section of the bridge includes Send and Return switching, which is bussed on 3 pin headers to all input sections, where it selects between the tape send (Direct Out) or return (Monitor) input. Power to the meter bridge is also conveyed on the D-type connector. There is a master calibration trimmer on the rear of each meter bridge PCB, which should be used to set the 0VU point of the bargraphs in that section, plus an individual bargraph offset trim which should be used to set the on threshold of the lowest LED in the bargraph. The offset trim will need to be re-adjusted if the lowest LED segment illuminates when there is no signal present. To access the trimmers, the relevant rear section of the meter bridge needs to be removed - this is possible without removing the entire meter bridge from the console.
5. Calibration Procedure. For the first channel installed: 1. +4dBu 1KHz tone to LINE input, Gain @ 0dB, Channel Fader @ 0dB. BUSS switch off, EQ off. Trim Channel Valve for +4dBu @ DIR OUT. 2. Route to all Groups and L/R. Group and L/R Faders to 0dB. a): With Channel Pan fully left, trim Group 1/3/5/7 and L Valves for +4dB at their respective OUTPUTS. Trim 1/3/5/7 and L METERS for 0VU. b): With Channel Pan fully right, trim Group 2/4/6/8 and R Valves for +4dB at their respective OUTPUTS. Trim 2/4/6/8 and R METERS for 0VU. 3. MIXB SOURCE to Channel, MIXB Master to 0dB, MIXB routed to L/R. a): b): 4. With MIXB Pan fully left, trim BL Valve for +4dBu at MIXB L OUT. Check +4dB at L OUT. With MIXB Pan fully right, trim BR Valve for +4dBu at MIXB R OUT. Check +4dB at R OUT.

MIXB SOURCE to MON. Input to MON, Mon Gain @ 0dB. Trim Mon Valve for +4dBu at MIXB R OUT.
Subsequent Channels: 1. +4dBu 1KHz tone to LINE input, Gain @ 0dB, Channel Fader @ 0dB. Trim Channel Valve for +4dBu @ DIR OUT. 2. MIXB SOURCE to MON. Input to MON, Mon Gain @ 0dB, MIXB Pan fully right, Trim Mon Valve for +4dBu at MIXB R OUT.