CONTENTS SCENARIO 1 INTRODUCTION UNPACKING VISUAL INSPECTION SPECIFIC POINTS 3 3 3 3 IMPORTANT SAFETY INSTRUCTIONS 6 POWERING 7 M-S NOTES 8 AD149 AUDIO MIXER 22 TECHNICAL SPECIFICATION 28 EQUALISATION CURVES 31 CONNECTOR PANEL CONNECTIONS 32 33 MODULE LAYOUT AND FUNCTIONS BLOCK DIAGRAM PART 1 MICROPHONE/LINE INPUT MODULE MONO LINE INPUT MODULE STEREO LINE INPUT MODULE BLOCK DIAGRAM PART 2 OUTPUT MODULE ADJUSTMENTS AND CALIBRATIONS MONITOR MODULE 37 38 46 50 55 56 60 64 MIXING 70 PLAYTI
SCENARIO Time was when it became necessary to update the ubiquitous AD145 PICO mixer. Our survey showed two main requirements: as well as Audio Developments' build and audio qualities, narrower and shorter modules were required, and the simple but effective equaliser from PICO had to be retained. By this time, 4-track recording equipment had begun to trickle into the marketplace (Nagra D etc), so we decided to give the new mixer four outputs.
Being latter-day converts, we have included circuitry to take full advantage of all M-S techniques - even shuffling - in both production and post-production. AD149 is Audio Developments' Blumlein. tribute to, and celebration of the genius of Alan We appeal to all AD149 users to break with tradition and, just on this occasion, study the manual to reveal all the mixer's secrets. THIS IS ESSENTIAL. Well - we HAD every intention that AD149 would complete the 140 series.
INTRODUCTION Unpacking If there are any signs of damage to the outside of the carton, please notify us or your supplier immediately, regardless of the unit's apparent physical condition. This is in case a claim has to be made at a later date because of previously undetected transit damage. The packaging material should not be discarded until the mixer has been acceptance tested and a suitable transit/storage case is available for secure, safe storage.
Fuses - to protect the mixer and internal power supply are mounted on the power supply/converter board. Access is gained by removing the output module. 20mm, 1A ANTI-SURGE HRC fuses are used - one for the internal battery power supply and one for the external DC supply. Limiter threshold - is set at the factory at +8dBu (PPM 6), but an internal preset potentiometer allows adjustment to any other level above 0dBu. The limiters are to be found on the left-hand PCB of the output module.
ABBREVIATIONS PPM VU VR X-Y A-B M-S peak programme meter volume unit variable resistor coincident stereo-microphone spaced-apart stereo-microphone middle-side; techniques and microphone described by A D Blumlein PCB printed circuit board HPF high pass filter ALL DIL SWITCHES ARE ILLUSTRATED AND SET AT THE FACTORY AS SHOWN ON BLOCK DIAGRAMS. (Refer to page 74 ) We wish you many trouble-free hours of use from your mixer. As a company, we are fully committed to BS EN ISO 9001.
WARNING IMPORTANT SAFETY INSTRUCTIONS The user of electrical products must be familiar with their potential dangers, and fundamental precautions must always be taken. Please read the following text carefully. Power supply units manufactured and supplied by Audio Developments Ltd are not user serviceable. There are no user-serviceable parts associated with any such power supply unit.
POWERING The mixer may be powered from either internal cells or an external DC power source. The integral battery compartment requires a total of 10 size-C cells. Access is gained via a captive lid which is retained by two, 90-degree-turn buckles. The lid hinges outwards 45 degrees from the back panel. When installing new cells, the row nearest the hinge should be fitted first. Either conventional dry, or rechargeable nickel-cadmium cells may be used.
M-S NOTES GENERAL BACKGROUND Of the various techniques that have evolved for stereophonic recording, the so-called COINCIDENT, NEAR-COINCIDENT and SPACED-APART techniques have found favour in the recording of classical music - being better suited to preserving natural perspectives and balances; whereas for the recording of popular music, the favoured technique is one which uses many microphones closely positioned to their sources for maximum isolation.
and ambience, whereas recordings made with X-Y techniques can suffer from centrestage high-frequency deficiency caused by the off-axis degradation of HF response of many directional microphones. Critical and discerning listeners are aware of the image shifting with changing frequency caused by less-than-perfect microphone polar patterns or the use of unmatched pairs of microphones.
COINCIDENT MICROPHONE TECHNIQUES (Intensity Stereo) A crossed pair of microphones is used with the capsules USUALLY arranged in a vertical plane and as close to each other as possible; the angle included by the capsules is symmetrical with respect to the central axis of the sound source. The angular accuracy of the stereo image is independent of the distance from sound source to microphone, but the resultant recording can seem rather dry and lacking a sense of space.
The use of hypercardioid capsules offers a good compromise between crossed pairs of cardioids and crossed pairs of figures-of-eight. The beam of a hypercardioid is narrower and the 'reach' longer than that of a cardioid, therefore these microphones can be used at a greater distance from the sound source for the same direct/reverberant sound ratio but, because of the presence of a rear pickup lobe, there is an increase in the sense of space.
(Note: it is assumed that M=S, ie the microphones have the same sensitivity and that there is the same amount of gain in each of the two signal paths.) When M>S M=omnidirectional: the resultant cardioids become more omnidirectional. M=cardioid: the rear lobes of the resultant hypercardioids are reduced in size and the included angle decreases. M=figure-of-eight: the included angle between the resultant crossed pair is less than 90°.
M-S / X-Y TRANSFORMATIONS (M=S) FIG 2 (An X-Y pair of cardioid microphones matrixes to a sub-cardioid and figure-of-eight microphone.) Sounds arriving where the M- and S-patterns intersect are reproduced fully left or fully right and define the included angle of sound which is spread completely between the loudspeakers. A very effective M-S combination for use where normally a single gun microphone would be used is a hypercardioid microphone (M) in conjunction with a figure-of-eight microphone (S).
SPOT MICROPHONES Very great care must be taken when using highlighting microphones within a stereo sound picture. When directional microphones are used, problems include blasting and proximity effects, and image shift as the sound source (soloist) moves. A 'spot' microphone can adversely affect the balance of the surrounding part of the sound stage and an insensitive engineer can easily make the microphone appear out of context with the overall stereo image.
In all circumstances, a camera-mounted stereo microphone is quite inappropriate. When it becomes necessary to employ spot or mono microphones for the majority of the pickup, the addition of a stereo pair will produce the impression of solidity and give a sense of presence, particularly when the main audio is ambience, as in sports events.
NEAR-COINCIDENT MICROPHONE TECHNIQUES These techniques provide good positional information together with a satisfying sense of space as they rely on both intensity and phase differences. The microphones are set close enough together to be effectively coincident at low frequencies and far enough apart for there to be a time delay between sounds from the left and right extremes of the sound source.
differences. Unlike a dummy-head, this microphone has a flat frontal frequency response and lacks those cues which give front/rear information in headphones listening and which only lead to colouration in loudspeaker listening. None of these near-coincident microphone techniques is strictly mono compatible. [Although the use of omnidirectional microphones is rightly preferred, wherever possible, by many engineers, it is worth recalling a few of their frequently overlooked characteristics.
overall level of the stereo signal. To steer the output of an M-S pair to any position within the final stereo picture, the outputs of the matrix amplifier are mixed, differentially, into the main L-R signal. [Refer to FIG 3(a) and FIG 3(b)] It is essential that the relative phase of all stereo signals is maintained. If X or Y is phase reversed, the stereo image will be imprecise with a lack of low frequencies. A mono reduction will now be the S-signal - which is not a normal audio experience.
SHUFFLING This is a fancy name for frequency-conscious width control and based - naturally - on Blumlein's work. By inserting an equaliser in the S-signal, the gain may be changed in a frequency-conscious manner which can lead to improvements in directionality in certain types of stereo recordings. To increase the width of a stereo image at a particular frequency or over a range of frequencies, the gain of the S-signal is increased at those frequencies.
By increasing the S-signal (over the full frequency range), the stereo image of some recordings can be extended beyond the left and right loudspeakers. This is yet another of Blumlein's discoveries and contained in the original patent. It is also a very useful technique for expanding the soundstage of a recording made, for whatever reason, with a too-narrow stereo image. Results may be dramatic but, equally, they may be phasey, confusing and unconvincing.
FURTHER READING British Patent Specification 394,325. A D Blumlein. Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing systems. British Patent Specification 780,337. P B Vanderlyn. Improvements in or relating to Binaural Sound Transmission Systems. British Patent Specification 781,187. P B Vanderlyn. Improvements in or relating to Electrical Sound Transmission Systems. Stereo Shuffling: New Approach - Old Technique. Michael Gerzon. Studio Sound: July 1986.
AD149 AUDIO MIXER In the new millennium (cliché), it is noticeable that sound recordists who work away from the controlled environment of the studio, wishing to produce a more nearlyfinished recording - requiring much less work in post-production - now demand more facilities and control from their portable mixers.
Our customers know we are totally committed to providing them with facilities for working in the M-S domain. The new monitor module enables engineers to take advantage of ALL Blumlein's techniques; both during recording and during postproduction. We believe that the monitor path is as important as the main signal-path and one that tells less than the whole truth is valueless.
An addition is the remote stop/start switch for use with suitably equipped tape recorders, eg Nagra IVS and D. Linked with this switch is the ability to automatically precede and terminate each recording with an ident tone - selected by a DIL switch mounted on the right-hand PCB. For some time now, line-up tone has proved controversial and contentious - a veritable hornet's nest.
however, a more important rôle: no longer do we have to tolerate the mixer output being limited because of the output from a particular microphone; the microphone can now be controlled at source. Odd/even pairs of microphone/line input modules may have their limiters linked for stereo operation by a DIL switch on the mother board - and situated between the relevant pair of modules. Past technical limitations have been responsible for these less-than-perfect ways of operating.
By combining the last two features, AD149 can be configured not only as a fouroutput mixer but also as two independently-controlled stereo mixers in the same chassis. Unusually for such a mixer, an ‘insert’ switch has been included in the microphone/line module for use during production. The availability of portable 8-track recorders enables up to eight microphone signals to be recorded separately, ensuring maximum flexibility during post-production.
It is intended that mono line modules shall be fitted in pairs - in odd/even positions within the chassis. Between the pair, a small PCB is plugged into the mother board, inserting matrix amplifiers across the pairs of modules - creating the same facilities as are available in the stereo line module. Unlike the microphone/line module, there is no gain in the auxiliary paths of the mono and stereo line modules - auxiliary level controls are attenuators only.
TECHNICAL SPECIFICATION - ELECTRICAL REFERENCE 0db=775mV at 1kHz unless otherwise stated MAX GAIN MIC LINE 80dB 45dB MAX INPUT LEVEL MIC @ MAX GAIN -42dB LINE @ MAX GAIN -7dB STEREO-RETURNS +18dB INSERT RETURN +18dB EXT 1 RETURN +18dB INPUT IMPEDANCE MIC LINE STEREO-RETURNS INSERT RETURN EXT 1 RETURN MIC POWERING 48v PHANTOM & 12v TONADER MAX OUTPUT +24dBm (600R LOAD) +24dBm (600R LOAD) +18dBm (600R LOAD) +18dBm (600R LOAD) +18dBm (600R LOAD) +18dBm (600R LOAD) OUTPUT IMPEDANCE <60R <20R <20R
NOISE MIC LINE EQUALISATION HF: LF: MF: <-126dB EIN 20Hz to 20kHz 200R SOURCE (with respect to the input) >70dB SNR 20Hz to 20kHz ±10dB @ 10kHz VARIABLE SLOPE ±15dB MAX @ 15kHz ±10dB @ 100Hz VARIABLE TURNOVER ±15dB MAX @ 30Hz ±15dB PEAK & DIP RECIPROCAL Q=1.
TECHNICAL SPECIFICATION - MECHANICAL AD149 is supplied with 6, 8, 10 or 12 input modules. A separate meter bridge fitted with 4 VU or PPM meters is supplied to read outputs Left, Right, Aux 1 and Aux 2. The mixer’s meters can then be dedicated to monitor outputs. A B 6 I/P 350 325 8 I/P 411 386 10 I/P 472 447 12 I/P 533 508 DIMENSIONS IN MILLIMETRES WEIGHT 6 I/P 8.4 8 I/P 10.0 10 I/P 11.6 12 I/P 13.
EQUALISATION CURVES AD149 HF and LF EQ Plot 20 15 10 5 dB LF Boost LF Cut 0 HF Cut HF Boost -5 -10 -15 -20 10 100 1000 10000 100000 Frequency AD149 MF and HPF EQ Plot 20 MF1 Boost 15 MF2 Boost 10 MF3 Boost MF4 Boost 5 MF1 Cut dB 0 MF2 Cut MF3 Cut -5 MF4 Cut HPF2 -10 HPF1 -15 HPF1&2 -20 10 100 1000 10000 Frequency 31 100000
CONNECTOR PANEL (1) (5) (6) (7) (8) (9) (18) (17) (16) Option-XLR & Jack in single housing (2) (4) (3) (1) (2) Microphone input Line input (10) (11) (3) Main Left-Right output (12) (4) (5) (6) (7) (8) (9) Auxiliary 1-2 output Left-Right return jack socket Auxiliary 1-2 return jack socket External 2 output jack socket Monitor 1 output jack socket Monitor 2 output jack socket (13) (14) (15) (16) (17) (18) 32 (11)) (12) (14) (13) (10) (15) Left-Right output/return multiway Left-Right ou
All input and output impedances and levels are to be found in the TECHNICAL SPECIFICATION. All inputs to, and outputs from AD149 are to be found on the connector panel. Module connector (1) accepts balanced microphones, line 1, stereo left Module connector (2) accepts balanced, line-level inputs, line 2, stereo right. XLR (Inputs & Outputs) Pin 1 Pin 2 Pin 3 Shield Signal + Signal - In the case of an unbalanced line-inputs and outputs, pins 1 & 3 should be connected.
The unbalanced, send outputs have low-impedance with a capability of driving headphones of 25 ohms impedance or greater. (Refer to page 68) The balanced (or unbalanced) signal from the outstation feeds on to the PFL mixing buss and is routed by grounding the control line (Pin 6) at the external source. Thus, a two-way conversation can take place between mixer and a boom operator with the boom operator being able to listen to programme when no communication is taking place.
HIROSE connectors (10) → (13) are provided for single-cable connection to the mixer. (10) & (11) and (12) & (13) can be used simultaneously. (10) carries the balanced L-R output and the unbalanced L-R return (stereo-return 1). (13) carries the balanced AUX 1 and AUX 2 outputs and the unbalanced AUX return (stereo-return 2).
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BLOCK DIAGRAM - PART 1 FIG 4 37
MICROPHONE/LINE MODULE (26) Channel insert jack (1) 48V phantom power (2) 12V tonader power (27) Input-gain control (3) Line input (4) Phase change (5) High-pass filter 1 (28) High-frequency control (6) High-pass filter 2 (7) Mid-frequency 1 (29) Mid-frequency control (8) Mid-frequency 2 (30) Low-frequency control (9) EQ selector (10) Channel insert (11) Aux 1 source selector (31) Auxiliary 1 level control (12) Auxiliaries ON (13) Aux 2 source selector (32) Auxiliary 2 level control (14) Auxili
FIG 5 39
The microphone amplifier has been described in detail in the introduction. Switches (1) and (2) select 48v phantom and 12v tonader power for condenser microphones. The switches are interlocked with tonader taking precedence over phantom. Powering may be selected before or after connecting the microphone, but switch off all powering on unterminated modules to ensure unconditional stability of the mixer.
Following the equaliser is an insert point, accessed via the standard 'A' type jack at the top of the module. Because of lack of PCB and panel space, input and output are, of necessity, unbalanced. Tip = send; Ring = return. The channel insert switch INST (10) enables external equipment to remain permanently connected to the channel. The insert socket is wired in order that a prefader channel signal is always present on the jack TIP.
changing phase of the S-microphone channel will rectify the situation - without having to disturb the microphone. But see, also, M-S NOTES.
The routeing switch (16) to the left and right mix busses is, in effect, the channel mute. Panoramic potentiometer - panpot - (33) routes the module's signal proportionately between the left and right mix busses. MON (18) routes the true (L/R) output from the module to the monitor module where it can be treated as an AFL (after-fader listen) signal or as an SIP (solo-inplace) signal. MON is independent of L-R routeing (16) and is derived from the output of the panpot and 'S' switch (15) if selected.
BOOM Once a module has been assigned to a boom microphone, DIL switch 1 mounted on the module's sub-board will route the signal to the monitor module where it can be independently selected to either or both of the external circuits, eg to boom operator and director/producer. This feature is operative when the DIL switch slider is moved to the right. Once this assignment has been made, we suspect it will remain in place during the lifetime of the mixer.
LIMITER CALIBRATION Refer to page 61, #1 for use of external test equipment. Switch off the limiter and set the presets for Release, Attack and Threshold to the centre. Set the bias preset on the main PCB - labelled SET 0 on FIG 6 - to its centre. Apply a 1kHz signal to the channel for a reading of 0dBu at pin 101 indicated on FIG 6. Turn SET 0 preset counter-clockwise until the reading at pin 101 reduces by not more than 0.2dB.
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MONO LINE MODULE (22) Channel insert jack (1) EQ split (2) Matrix 1 (23) Input-gain control (3) Line-input 2 (4) Phase change (24) High-frequency control (5) High-pass filter 1 (6) High-pass filter 2 (7) Mid-frequency 1 (25) Mid-frequency control (8) Mid-frequency 2 (26) Low-frequency control (9) EQ selector (10) Auxiliary 1 ON (11) Aux 1 source selector (27) Auxiliary 1 level control (12) Auxiliary 2 ON (13) Aux 2 source selector (28) Auxiliary 2 level control (14) Auxiliary stereo link (15) M
FIG 7 48
For optimum performance at line level, this module employs a double-balanced, instrumentation-grade input amplifier (3 x ICs) rather than the inferior differentiallybalanced amplifier (1 x IC). Isolation between the two inputs (Line 1 and Line 2) is so high, they may remain connected to the mixer simultaneously. Line 2 input is selected by switch (3). Following the input amplifier is the continuously-variable, input-gain control (23) and phase change (4).
These two matrix amplifiers may be inserted across the signal paths to create a 'Blumlein Loop' within which input gains can be used to change stereo width (or rebalance a L-R input), phase can be used to reorientate the L/R output from the modules and insert points to introduce FLEX-EQ for shuffling. Following MTX 2, the faders are available to steer the L/R output to its correct place within the final L-R picture.
STEREO LINE MODULE (20) Left-path insert jack (1) Matrix 1 (21) Right-path insert jack (2) Input reverse (3) Phase change (4) High-pass filter, left (22) Input-gain control (5) High-pass filter, right (23) Input-balance control (24) Channel-output steer control (6) Matrix 2 (7) Auxiliary 1 ON (8) Aux 1 source selector (25) Auxiliary 1 level control (9) Auxiliary 2 ON (10) Aux 2 source ssselectorselectror selector (26) Auxiliary 2 level control (11) Auxiliary stereo link (12) Left-path selector (2
FIG 9 52
We have already stated our philosophy behind this module and the reason for the omission of limited and limiting equalisation. As with the mono line module, the stereo line module employs (two) double-balanced, instrumentation-grade input amplifiers for optimum performance at line level. It is important to notice that, unlike typical stereo modules, the two signal paths remain separate from the input to the output of the module - thus enabling different equalisation to be applied to each signal path.
have to apply an HPF to the S-signal only, in order to reduce low-frequency content (with respect to the M-signal). Still within the 'Blumlein Loop' is the input-balance control BAL (23). For maximum flexibility, this control is zero-to-zero, ie when fully anti-clockwise, only the left-hand signal is available and when fully clockwise, only the right-hand signal is available. This control changes the width of a stereo signal from mono to enhanced stereo (through to a meaningless S-signal).
We believe that mono auxiliaries are related to the module’s input signal rather than its output signal, therefore post-fader auxiliaries are derived pre the steer control and L or R or L+R selection. Similarly, we believe that a stereo auxiliary is related to the module’s output; therefore when (11) is selected the auxiliary signal is derived post the steer control. Selective use of BAL (23) and STEER (24) allows different balances to be achieved on stereo auxiliary and the module’s stereo output.
BLOCK DIAGRAM - PART 2 FIG 11 56
OUTPUT MODULE (7) Mixer ON LED (8) Battery indicator switch (1) Meter 1 (9) Meter illumination switc (10) L-R or Aux 1-2 to meter (11) Monitor 1 to meters (12) PFL to meters (2) Meter 2 (22) Remote stop/start (13) 1kHz or 10kHz line-up t (14)Continuous or interrupte line-up tone (3) Limiter LEDs (4) L-R output limiters (15) Line-up tone to L-R outp (16) Line-up tone to auxiliary outputs (5) Limiter link (6) L-R output matrix (17) Aux outputs matrix (20) Aux 1 master control (18) Output fader left
This module controls all metering of PFL and output signals, and also the level of main and auxiliary output signals. Calibration is achieved when the faders and auxiliary potentiometers are at maximum. The upper meter (1) reads left output, auxiliary 1, monitor 1 left, PFL left and the lower meter (2) reads right output, auxiliary 2, monitor 1 right, PFL right - by use of switches (10), (11), (12).
Line-up tone, when selected, replaces the normal signals on the main, L-R output (15) and on the auxiliary outputs (16). The frequency of line-up tone may be selected between 1kHz and 10kHz (13). Tone is normally continuous on L & R and on AUX 1 & 2 or interrupted tone, in 3-second bursts, may be selected to L and AUX 1 by switch (14).
REMOTE REM (22) is a latching switch to start and stop a tape recorder fitted with a remote stop/start function. Via a DIL switch on the right-hand PCB, it can be arranged for each recording to be 'topped and tailed' with a marker, ie a few seconds of low-frequency tone. To INHIBIT the marker tone, set DIL switch to the left.
ADJUSTMENTS AND CALIBRATIONS Meters - are to broadcast specification and either a VU or a PPM may be selected. A choice of 3 scales is available for the PPM: BBC, N10, SDR. Line-up-tone oscillator - the preset (VR4) that adjusts its level at the outputs of the mixer is mounted on the right-hand PCB of the output module and can be adjusted from the copper foil side of the board.
VU meter - there is one preset, on the VU meter PCB, for meter adjustment. Set an input module for a line input and introduce a 1kHz tone from an audio signal generator. Adjust levels to achieve a reading of +4dBu, at a main output, on an AC millivoltmeter - measured across pins 2 & 3 on the output XLR. Switch the appropriate meter to the selected output and adjust the preset to give a reading of 0VU. PPM meter - the driver PCB has three calibration controls (presets).
Main-output limiters - calibration involves two presets per output. Using the 'L' output as the example and referring to FIG 12 … Biasing and threshold are adjusted as follows: VR1 biases the limiter circuit to the point of correct operation and VR2 sets the threshold. (Labelled SET 0 and THR respectively on the left-hand PCB.) Determine whether the left-hand PCB is issue 3 and below or issue 4 and above. If issue 4+, read ‘PIN 5 of IC2’ instead of ‘PIN 12 of IC1’ in the following paragraphs.
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MONITOR MODULE (1) Channels to monitor (2) L output to monitor (3) R output to monitor (4) L-R output to monitor (20) Return 1 calibration control (5) Stereo-return to monitor (6) Aux 1 output to monitor (7) Aux 2 output to monitor (8) Aux 1-2 output to monitor (21) Return 2 calibration control (9) Stereo-return 2 to monitor (22) Split monitor (10) Monitor 1 output-level control (23) Matrix 1 (11) Monitor 1 balance control (24) External 2 level control (12) Monitor 1 output dim (25) External 2 ON (13)
The monitor module is associated with all aural monitoring of input and output signals together with communications between the sound operator and two outstations EXTERNAL 1 & 2. (Metering of monitor 1 is performed pre fader and matrix amplifiers. Metering of PFL is performed pre fader.
CH (1) operates in conjunction with the MON switch on the channels. This MON signal is the same as that which drives the left and right mix busses. If MONO (14) is also selected, the monitored signal becomes a true (mono) AFL (after-fader listen) signal from the channel. "How does a microphone signal sit in the mix?" By alternating CH (1) and L-R STEREO (4) and routeing the appropriate microphone channel to MON, the question is easily answered.
may be disabled by DIL switch (3) on the left-hand PCB. (Refer to FIG 15) Use of split monitoring makes no change to the meters when reading monitor 1, but note that a signal entering monitor 1 path in the M-S domain will mix to monitor 1 left as a stereo-left signal - as it will when MONO (14) is selected. Once the correct level has been set for monitor 1 output (10), the level of this signal to the headphones can be further adjusted by the monitor 2 level control (15).
EXTERNAL 1 & 2 AD149 has the capability of sending signals to two outstations - external 1 and external 2. It is suggested that external 1 be used by the boom operator as it has the facility to talk back to the mixer - it also lacks a level control and on/off switch as these will be available on the operator's belt pack. External 2 has been designed to drive headphones for use by a director/producer etc.
COMMUNICATIONS In order that the sound operator can communicate with any output, the safety switch (Comms Master) ON (29) must be selected: L-R (18) routes the internal microphone to the main output and AUX (19) routes the internal microphone to both auxiliary outputs. [Switches (18) and (19) have a momentary action, ie they are non-latching.] EXT 1 (17) and EXT 2 (32) route the signal from the internal microphone to replace any signal appearing on EXT 1 and EXT 2 outputs.
MIXING We have already established that, during post-production, it is desirable for signals to be in the L-R domain at the input to the fader of stereo modules - but not necessarily stereo pairs of mono modules - in order that auxiliaries shall be meaningful. (Refer to page 53) During recording/production there are eight possible signal paths through the mixer: inputs to the module in M-S or X-Y; mixing in the M-S or L-R domain; mixer output in M-S or L-R.
X-microphones will be panned hard left, and Y-microphones will be panned hard right. Spot microphones will be panned to their correct position in the final L-R image. Earlier we mentioned conflicting monitor requirements; a problem arises when monitoring an S-channel after its S-switch has been selected.
MIXER PATHS FIG 17 73
PLAYTIME The following experiments may be performed on the monitor module. Select a couple of L-R recordings; one in natural stereo and with a centralised soloist, and one in unnatural, panpotted stereo. The object of the exercise is to compare and contrast the two possible mono reductions. The simplest method is to add the left and right signals - but remember those nasty phase distortions. The second method is to matrix the L-R input signal to M-S and extract the M-signal only.
DIL SWITCHES MOTHER BOARD Link → DIL 2 DIL 3 Pre fader Select ↓ ↑ DIL 1 Select → Pre fader → Fast Slow Fast Slow ← → ← → Disable ← DIL 3 Disable → EXT 1 - CH/MON bypass DIL 1 EXT 1/R - talk + monitor DIL 2 MON 1 Enable ← ← Input limiters MIC/LINE MODULE Main PCB Clean feed Private line Sub-board Boom MONO LINE MODULE Main PCB Clean feed OUTPUT MODULE Left-hand PCB Limiter attack Limiter release Right-hand PCB Ident marker tone MONITOR MODULE Left-hand PCB Split - monitor 2 Right-hand
POWER SUPPLY UNIT TYPE AD100-09 The AD100-09 mains POWER SUPPLY UNIT is suitable for driving most of AUDIO DEVELOPMENTS’ range of portable audio mixers. This PSU is a single-rail device providing 500mA of current at +14v DC potential and is used as a substitute for battery power with mixers containing an internal DC-DC converter. The AD100-09 may be powered from either a 110/120v AC source or a 220v/240v AC source.
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CUSTOMER NOTES AND FACTORY MODIFICATIONS 78
TECHNICAL LIBRARY 79
