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AD149 - Zeigermann

1. Return 1 calibration control Return 2 calibration control Split monitor Matrix 1 External 2 level control External 2 ON Boom mic to external 2 External 1 amp 2 source Boom mic to external 1 29 Communications master Internal microphone Internal microphone level 32 Talk to External 2 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 8 2 Metering of monitor 1 is performed pre fader and matrix amplifiers Metering of PFL is performed pre fader It is necessary to be able to audition in left right stereo ie a form the human brain understands an X Y or A B stereo microphone and an M S stereo microphone whether the channel panpots are set centrally or hard left and hard right thus creating conflicting monitor reguirements It is also necessary to be able to audition X Y M S in isolation Similarly facilities must be provided to monitor main and auxiliary outputs whether they be in the M S or L R domain It is a bonus to be able to determine the potential of these various signals in their after life ie in post production The signal s to be auditioned on the left and right unbalanced outputs of monitor 1 and monitor 2 will be selected from the bank of switches 1 to 9 These switches are not interlocked in order that any desired mix of signals may be achieved Swi
2. AT lt ma HI L3WZNOW EH n Txny LI VI WIT Lar p ve ina T xnv l auch RR r lt q bom L3W NOW K swa Non Oot TE f HT SAIN Da 4 l u re gt anent pa La lo 7 5 7 Ki swa a KK x M 2 MS TIQ INT7INOD Dera T a h a 2 pig 2e 0334 SEX E wl Usd NE L Se awal ly IL NI LNO JJ IZZ xx gt gt asonvivann EEEL a TULE 36 FIG 4 37 MICROPHONE LINE MODULE 1 48V phantom power 2 12V tonader power 3 Line input H Y____ O 5 High pass filter 1 6 High pass filter 2 Avata O seer 48V PH MINGAIN Max Te LAES 4 Phase change 7 Mid freguency 1 8 Mid frequency 2 SO MF 9 EQ selector 10 Channel insert 11 Aux 1 source selector 12 Auxiliaries ON 13 Aux 2 source selector 14 Auxiliary stereo link 15 Matrix 16 Routeing to L R output mute 17 Limiter 18 Routeing to monitor 19 Pre fade listen 20 PFL indicator LED 21 Overload LED 22 Limiter LED 23 Release 24 Attack 25 Threshold O oe oo AUX 1 10 ON PAN r POST oo AUX2 10 LIM 5 10 PFL 5 O 0 O OL O 5 LIM 10 Q REL 20 v 30 TH LO 50 00 38 26 Channel insert jack 27 Input gain con
3. 4 Right Aux 2 Signal 5 Ret1 R Ret2 R Signal 6 Shield Shield 7 Ret 1 L Ret 2 L Signal 8 Shield Shield 9 Shield Shield 10 Shield Shield 11 carries an unbalanced L R output and unbalanced stereo return 1 for connection to a camera or DAT recorder 12 carries unbalanced auxiliary outputs and unbalanced stereo return 2 for connection to a camera or DAT recorder L R AUX Pin 1 Left Aux 1 Signal 2 Right Aux 2 Signal 3 Shield Shield 4 Ret 1 L Ret2 L Signal 5 Ret 1 R Ret 2 R Signal 6 Shield Shield POWER OUT 18 is a 4 pin HIROSE connector to supply 12V DC 100mA to power external equipment eg two non diversity radio microphones Pin 1 Power ground 2 Power ground 3 DC 12V Switched 4 DC 12V Unswitched Pin 3 depends on the position of the mixer ON OFF switch Connector 18 may also be used for powering two or three PORT A FLEX units Each unit has an in and an out power socket so that several units can be daisy chained Typical usage could be FLEX EQ a headphone distribution amplifier 35 and a four output stereo distribution amplifier BLOCK DIAGRAM PARTI OT F 4 MS 110 zxnv 134 ki Met 210029 TXNY 138 6e 4 XIV U 134 T MS ara ka T 138 WI ino 2 A
4. FIG 1 This spacing which does not apply to other directional microphones actually improves stereo imaging Samm oa A 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 The narrower beam is a slight disadvantage in that in order to provide a solid central image the included angle must be less than that for a pair of cardioid microphones Hence this system is not entirely suitable for wide sound sources The M S technique was rediscovered by Lauridsen and uses a microphone M aimed along the central axis of the sound source and a figure of eight microphone S at right angles to this axis it is assumed that the positive lobe is orientated to the LEFT for the purposes of these notes The outputs of the microphones are combined in a sum and difference matrix amplifier to produce conventional left and right stereo signals Later summation of the L R signals to produce a compatible mono signal is more predictable than when using stereo signals recorded using other formats 2M alternatively the original M signal can be used Thus by careful c
5. type stereo jack MON 1 8 Monitor 2 headphones output appears on an A type stereo jack 9 This output is capable of driving 25R at OdB EXT 2 7 is a mono unbalanced jack carrying monitor signals to a second outstation MONO UNBALANCED JACK STEREO UNBALANCED JACK Tip Signal Tip Left Signal Ring Shield Ring Right Signal Sleeve Shield Sleeve Shield Channel insert jack Tip send Ring return The 6 pin XLR connector EXT 1 17 carries all signals to and from an outstation The balanced return appears only on the headphones output XLR Pin 1 Shield Pin 4 Ret 2 Send Left 5 Ret 3 Send Right 6 Control 33 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 A three position rocker switch BATT EXT 14 selects either internal batteries or an external DC source Power to the mixer is confirmed by the MIX ON LED on the output module This LED flashes when the internal voltage falls below the safe operating level of 10V External powering of the mixer is via a 4 pin XLR 15 XLR Pin 1 OV
6. Body DC OUTPUT XLR PIN 1 OV PIN 3 NOT CONNECTED PIN 2 CHARGE PIN 4 14V DC DO NOT REMOVE THE OUTER COVERS NOTE The power supply unit should be serviced by a suitably qualified engineer Only genuine spare parts with identical specifications must be used It is dangerous to change the specification or modify the product in any way 66 CUSTOMER NOTES AND FACTORY MODIFICATIONS 67 TECHNICAL LIBRARY 68
7. FIG 17 Whichever path is selected no constraints will be placed on the auxiliaries as mixing in the M S domain is a legitimate technique When auxiliaries are not being used for usual applications they may be used to create a mix different from the main mix or identical with it but in the opposite domain A recording made in the M S domain will be ready for the application of all possible post production techniques Of the eight paths through the mixer we believe that numbers 1 2 and 3 will be the ones most frequently used with 4 amp 4a having no likely usage When using stereo microphones it must again be stressed that odd numbered modules are occupied by the X A M microphone and that even numbered modules are occupied by the Y B S microphone A combination of M S X Y and spot microphones may be mixed either in the L R domain or the M S domain In each case the stereo microphone must be matrixed to the appropriate mixing domain When all inputs are in X Y form mixing will normally be done in the L R domain Blumlein s microphone techniques have advantages over all others X Y and A B such that it is worthwhile using M S microphones even when mixing is to be done in the L R domain For example the M microphone will be placed in the optimum position for a mono image whereas mixing to mono the signals from an X Y stereo pair introduces phase anomalies Any M S microphone or input will be in the M S domain at the pre and post fad
8. Pin 3 NC 2 Charge 4 12V 15V DC A suitable external power supply is Audio Developments AD100 09 but any external DC source must be capable of delivering 750mA at 12V SUB 1 16 is a 15 way D connector which may be used to drive an external meter bridge and supply the necessary DC voltages The four meters read Left Right Auxiliary 1 and Auxiliary 2 outputs When a meter bridge is being used the mixer s meters may be routed permanently to monitor 1 or PFL All signals are unbalanced SUB 1 is also employed when a recorder is to be controlled remotely CONV IDC CONV IDC PIN 1 1 Chassis PIN 8 15 V voltage rail 2 3 Spare 9 2 OV 3 5 N C contact Remote 10 4 PFL left output 4 7 Common Remote 11 6 PFL right output 5 9 N O Contact Remote 12 8 Aux 2 output 6 11 PFL control 13 10 Aux 1 output 7 13 V voltage rail 14 12 Right output 15 14 Left output CONV refers to the normal numbering of a D type connector but note that some IDC types are numbered as indicated in 34 HIROSE connectors 10 13 are provided for single cable connection to the mixer 10 8 11 and 12 8 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 L R AUX Pin 1 Left Aux 1 Signal 2 Left Aux 1 Signal 3 Right Aux 2 Signal
9. in the centre of a wide stage or expanding the stereo image and adding ambience on long shots and if mono compatibility is of great importance this format is the clear winner The majority of the listening audience still hears a mono mix It has been shown that more ambience is preferred when listening in stereo than when listening in mono Recordings made using the M S technique satisfy these preferences as the presence of the S signal increases ambience with the M signal being true mono Because of the way the pair of microphones responds to reverberant information a well done M S recording preserves a high degree of realism When using the M S technique the microphone system can be positioned in order that the forward facing capsule produces the optimum mono signal with the best possible frequency response whilst maintaining easily adjustable stereo perspective and ambience whereas recordings made with X Y techniques can suffer from centre stage 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 These same listeners will also be disturbed by the phasing effects caused by the movement across the faces of badly positioned spot or highlighting microphones and by the fact that images at l
10. 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 The return signal from EXTERNAL 1 is fed to the PFL mix busses and PFL level to monitor 2 is set by potentiometer 16 to be balanced against monitor 1 level on monitor 2 path MONITOR MODULE PCBs FIG 15 DIL 1 selects MON 1 only facility to EXT 1 bypassing CH MON 27 switch DIL 2 selects talk monitor facility on EXT 1 DIL 3 selects facility of SPLIT MONITOR 22 on monitor 2 output 58 EXTERNAL 182 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 External 2 has its own on off switch 25 and screwdriver operated level control 24 but has no provision for talking back to the mixer At all times a monitor signal will be present
11. lt z NZ M S AR X Y M S CH e 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 However during our research it has been made very clear to us that the Sennheiser MKH 416 short gun microphone is going to be a very popular choice for the M signal When using gun microphones for the M signal it must be borne in mind that they become more directional with increasing frequency and have LF and MF side lobes Very odd effects can arise if used against a moving background A stream of traffic say will change its perspective as it moves across the various lobes It should be noted that the sensitivities of the 12V tonader and the 48V phantom powered versions of this microphone are not the same 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
12. of the sound stage and an insensitive engineer can easily make the microphone appear out of context with the overall stereo image As the signal from the soloist s microphone arrives in the mix ahead of the basic pickup one solution is to delay this signal 10 15ms with respect to the main signal or even to fall in the region of early reflections another is for just sufficient of this signal to be added to the mix to increase the presence of the soloist Precise positioning of the spot microphone within the overall picture is essential in order that the image does not shift with changing frequency and intensity When using the X Y format a crossed pair of omnidirectional microphones with an included angle of 60 90 provides a very stable image of the soloist without blasting or proximity and directionality effects but with a well defined sense of space When using the M S technique further M S pairs can be used as soloists microphones each subsidiary pair will be steered to its correct position within the sound stage and its included angle will be less than that of the main pair So that maximum flexibility is maintained during post production these spot microphones will be recorded on separate pairs of tracks on the tape For ENG interview work it is perhaps legitimate to adopt a less purist approach without making too many compromises A mono microphone may be mixed into the M channel ONLY with the result that its image will take
13. production a monitor signal in the L R domain may have its potential evaluated by converting to M S with MTX 1 23 and width changed before re converting to L R MTX 2 13 Also when in the L R domain the monitor signal may be steered BAL 11 to match a visual image MTX 2 13 will also reveal mono compatibility M of a L R stereo signal on monitor 1 left and out of phase components S on monitor 1 right Both of these signals may be isolated using the BAL control perhaps in conjunction with the MONO 14 switch Similarly any M S signal appearing on monitor 1 may have its M S relationship changed using the monitor BAL control 11 without affecting any previous settings before being converted to L R by MTX 2 13 Operating on monitor 1 is a dim control 12 which lowers the output by 20dB This dim function is automatic when the internal microphone 30 is routed to L R 18 and or AUX 19 outputs Dim does not affect a monitor 1 signal that is routed to the headphones The relationship between monitor 1 monitor 2 headphones and PFL has been fully described on pages 22 amp 23 Split monitoring is a facility unique to AD149 and operates on both monitor 1 and monitor 2 outputs the function being selected by SPLIT 22 Split monitoring is set at the factory to operate simultaneously on monitor 1 and monitor 2 when SPLIT 22 is selected but if not required on 57 monitor 2 this may be disabled by DIL switch 3 on the
14. 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 Because of the spacing between the capsules large image shifts can stem from quite small movements within the sound source hence close miking is not advisable Also sounas arriving from the extremes of the sound source may cause problems when deriving a compatible mono signal and when disc cutting There are four main near coincident techniques e The ORTF technique was developed by the French broadcasting organisation Two cardioid microphones are spaced 170 mm apart with an included angle of 110 e The NOB system was developed by the Dutch broadcasting organisation Two cardioid microphones are spaced 300 mm apart with an included angle of 90 e A system developed by Faulkner uses two forward facing figure of eight microphones spaced 200 mm apart The microphones are positioned further back from the sound source than is usual with other near coincident techniques The results show many of the qualities of the Blumlein technique and a natural balance between close and distant elements within the sound source e The binaural technique was specially developed for listening to playback on headphones but the recordings are considered by some listeners to be
15. type the other for IDC Refer to connection details on page 33 50 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 Refer to FIG 13 Low battery indicator the preset VR3 associated with this facility is mounted on the right hand PCB of the output module The low reading is set at the factory and corresponds to a set of batteries having discharged to 10V Ona VU meter low volts is at OVU On a PPM meter it is indicated by a separate marking yellow on a BBC scale and red on an N10 and SDR scale Refer to FIG 13 FIG 14 51 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 8 3 on the output XLR Switch the appropriate meter to the selected output and adjust the preset to give a reading of OVU PPM meter the driver PCB has three calibration controls presets VRI adjusts the reference level VR2 and VR3 adjust the law of the m
16. unsatisfactory when heard on loudspeakers This system uses a dummy head usually made from polystyrene with omnidirectional microphones placed into the ears This technique provides excellent imaging in both horizontal and vertical planes A development of the technique uses two omnidirectional or figure of eight microphones set approximately 90 mm on either side of a circular non reflective baffle This allows sufficient leakage between the microphones to make reproduction over loudspeakers a satisfying experience In recent times attempts have been made to bring to loudspeaker listening the naturalness and the depth and sense of space present when listening on headphones to dummy head recordings These features are usually missing from recordings made with coincident X Y microphones To this end it is necessary that the signals have a natural interaural relationship but this can only be achieved with some form of dummy head technique The Schoeps KFM6U sphere microphone has been designed to satisfy these requirements A 180 mm diameter sphere has two omnidirectional microphones set on opposite sides of the sphere and produce a stereo signal with natural interaural 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 t
17. up a central position in the final L R stereo presentation During post production the width and ambience of the background may be changed but the balance between the M S pair and the mono microphone remains fixed If a single M S pair is used the M microphone should be pointed between the interviewer and the interviewee This technique will provide a more stable and coherent image than mixing into the M channel a microphone moving between sources and consequently with a changing background unless this microphone is so close to the source that its background pickup is negligible compared with the pickup of the M S pair If an M S microphone is too close to the sound source small movements of the source lead to large changes in the angle of incidence and thus excessive movement in its position within the sound picture This is particularly true when the S signal has a high gain Conflict will occur when the situation demands a close mic position for the sake of clarity 14 In all cireumstances 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 15 NEAR COINCIDENT MICROPHONE TECHNIQUES These techniques provide good positional information together with a satisfying
18. wider the position of dialogue can be changed within the stereo image without affecting the stereo ambience and equalisation can be applied without affecting the mono signal 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 Similarly to reduce the width of a stereo image at particular frequencies the gain of the S signal is reduced at those frequencies Later research has suggested that an equaliser should also be inserted in the M signal so that when the S signal is increased at specific frequencies the M signal may be reduced slightly at the same frequencies in order to maintain overall frequency balance Similarly if the S signal is reduced then the M signal is increased slightly at the same frequencies Graphic equalisers would appear to be the obvious choice for shuffling but they are made up of a series of narrow band therefore ringy filters and this can lead to a ripply frequency response Far better results will be obtained by using a constant Q parametric equaliser with a very low Q setting eg 0 2 so that just one filter
19. will be panned hard left X and hard right Y and any spot microphone will be panned to its correct position in the final L R image CH 1 on the monitor module and MON selected on both channels of an X Y pair auditions each stereo microphone MON on a spot microphone is solo in place usage of the monitor system When monitoring an X Y microphone MTX 1 BAL MTX 2 will reveal the potential of angular changes to the microphone or possibly a change of position without having to gain access to the microphone All auxiliary sends will be in the L R domain 62 MIXER PATHS BOLINO gt 8 AILIN BILIN gt id Lao 43074 gt 1Nd1N0 14990601 FIG 17 63 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 At this stage take the opportunity of also auditioning the out of phase components S signal Throughout the experiment note the effect of introducing the phase inversion switch on the right input signal C
20. 6 space was at a premium by the time we arrived at the monitoring section and several what appeared to be compromises had to be made The compromises proved so flexible and versatile they have been retained in all succeeding models Because of space constrictions monitoring had to be simplified with the following result The main monitor path MONITOR 1 is addressed via the MON switch on each input module The secondary monitor path MONITOR 2 feeds the stereo headphones jack and is addressed via the PFL switch on each input module BUT monitor 1 output automatically drives monitor 2 output until any PFL switch is pressed 22 when logic changes the source of monitor 2 output to the stereo PFL busses When all PFL switches are released once again monitor 2 equals monitor 1 This system has now been refined even further when using monitor 1 as the main monitor probably for loudspeaker listening it is possible to route PFL which normally only appears on headphones to monitor 1 by selecting SPLIT monitor Pressing a PFL switch will now have the following effect any stereo signal being auditioned on monitor 1 will be mixed to mono and presented to monitor 1 left output only PFL will be mixed to mono and presented to monitor 1 right output only As will be seen later page 54 mono PFL can be isolated and presented to both left and right outputs simultaneously The monitoring system allows an input channel to be audi
21. 7 Separate Penny amp Giles output faders 18 and 19 are employed for maximum flexibility but may be linked by a ganging clip A pair of limiters may be switched into the main L R output LIM 4 and linked for stereo operation LINK 5 A choice of fast or slow attack and release times may be made via the two DIL switches on the left hand PCB When the limiters are being used as a stereo pair they should have their attack times and release times set identically LEDs 3 indicate when limiting is taking place A matrix 6 may be inserted in the main L R output path LEFT HAND PRINTED CIRCUIT BOARD NOTE WHEN DIL Sw IN ON POSITION ATT AND REL IN FAST MODE FAST RH OUTPUT FIG 12 48 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 amp R and on AUX 1 amp 2 or interrupted tone in 3 second bursts may be selected to L and AUX 1 by switch 14 By the simple addition of two links cutting a track and removing a through pin on the right hand PCB the user may more logically place the interrupted tone on the R and AUX 2 outputs Line up tone is calibrated on the BBC scaled meters to PPM4 giving a line output level of OdBu with L amp R and AUX 1 amp 2 controls set to maximum Alternative calibration levels are poss
22. 70mA 29 TECHNICAL SPECIFICATION MECHANICAL AD149 is supplied with 6 8 or 10 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 350 411 472 B 325 386 447 DIMENSIONS IN MILLIMETRES WEIGHT 6 I P 8 P 10 I P 8 4 10 0 11 6 WEIGHTS IN KILOGRAMS 30 EQUALISATION CURVES AD149 HF and LF EQ Plot 20 10 100 1000 10000 100000 Frequency AD149 MF and HPF EQ Plot 10 100 1000 10000 100000 Freguency 31 LF Boost LF Cut HF Cut HF Boost MF1 Boost MF2 Boost MF3 Boost MF4 Boost MF1 Cut MF2 Cut MF3 Cut MF4 Cut CONNECTOR PANEL 1 5 6 7 8 9 48 QUTPUTS SUB 1 a 5 RET PF 17 V YON W 16 AUX 1 AUX 2 LEFT RIGHT OO U POWER Option XLR amp Jack in single housing 2 4 Microphone input Line input an N 3 Main Left Right output Auxiliary 1 2 output Left Right return jack socket Auxiliary 1 2 return jack socket External 2 output jack socket Monito
23. ABBREVIATIONS PPM peak programme meter VU volume unit VR variable resistor X Y coincident stereo microphone A B spaced apart stereo microphone M S middle side techniques and microphone described by AD 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 Should you have any problems or require any further information on FLEX EQ or the M S microphone technique please do not hesitate to contact us on 01543 375351 or by fax on 01543 361051 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 by Audio Developments Ltd are not user serviceable There are no user serviceable parts associated with any such power supply unit THE OUTER COVERS MUST NOT BE REMOVED Such a power supply unit is solely for use with audio mixers and sound processors hereafter called the equipment manufactured by Audio Developments Ltd Always use a cord set accepted by a National Approved Body EARTHING GROUNDING When using an external power supply unit that is connected to the mains supply to drive the mixer it must be CONNECTED TO EART
24. CONTENTS SCENARIO INTRODUCTION UNPACKING VISUAL INSPECTION SPECIFIC POINTS IMPORTANT SAFETY INSTRUCTIONS POWERING M S NOTES AD149 AUDIO MIXER TECHNICAL SPECIFICATION EQUALISATION CURVES CONNECTOR PANEL CONNECTIONS MODULE LAYOUT AND FUNCTIONS BLOCK DIAGRAM PART 1 MICROPHONE LINE INPUT MODULE BLOCK DIAGRAM PART 2 OUTPUT MODULE ADJUSTMENTS AND CALIBRATIONS MONITOR MODULE MIXING PLAYTIME DIL SWITCHES AD100 09 POWER SUPPLY UNIT CUSTOMER NOTES AND FACTORY MODIFICATIONS TECHNICAL LIBRARY OOO 22 27 30 61 62 63 64 65 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 Because of the lower noise floor of modern digital recorders the level of input signals may be reduced We have taken advantage of this fact and lowered the slope ratio of the limiters to 7 1 By so doing not only is signal distortion greatly reduced but also the artefacts associated with limiters become much less noticeable or objectionable Also sixty years after the event sound engineers have come to realise the potential of Blumlein s M S
25. H In certain types of malfunction or breakdown earthing provides a path of least resistance for electric current and considerably reduces the risk of electric shock DANGER Incorrect connection of the equipment grounding earthing conductor can result in the risk of electric shock Where possible obtain a pre wired mains lead from a reputable supplier with the correctly fitted mains connector for the type of mains outlet in use otherwise one correctly wired and checked by a qualified electrical engineer If your mains lead is not suitable for the mains outlet have the correct plug fitted by qualified personnel The MAINS PLUG of this equipment is the primary disconnect device Therefore in the final application ensure it remains close to the equipment and easily accessible 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 NICADs may be recharged in situ through the 4 pin POWER IN connector The circuit for recharging is already incorporated within the mixer A voltage in the range 15V to 24V DC 250MA is required on PIN 2 of the POWE
26. IN INI te a TW Ii 2v T1Vo o et 8 10 A Jdo e d 1 134 240 T a k Q S SV Sg 7 5 S ev iVvo e k ev fo 7 a x j 43134 WOLL09 ad ev YTY 1 Tdd ILIW dOL WA 10 l H20 MONITOR 1 RIGHT MONITOR 1 LEFT PFL RIGHT PFL LEFT PFL CONTROL PRIVATE LINE BOOM FIG 11 46 OUTPUT MODULE 1 Meter 1 2 Meter 2 3 Limiter 4 L R output 5 Limiter link 6 L R output matrix 18 Output fader left 19 Output fader right F AW Developments Ltd OW a 4 5 B AN Lisa OF Of L R m AUX Oi Si A A 7 Oi 1K m a LO OR INT O LIM TONE HR O LINK AUX i MTX MTX 5 oo Q 10 AUX OE l d 15 H eee Q _og STEREO 30 4O 50 70 00 L R 47 7 Mixer ON LED 8 Battery indicator switch 9 Meter illumination swit 10 L R or Aux 1 2 to mete 11 Monitor 1 to meters 12 PFL to meters 22 Remote stop start 13 1kHz or 10kHz line up 14 Cont
27. R lt 20R lt 20R lt 20R lt 20R FREQUENCY RESPONSE HARMONIC DISTORTION OVERLOAD INDICATOR POINT CROSSTALK 18dBm 600R LOAD CLEAN FEED UNBALANCED L R and AUX 1 amp 2 MONITOR 1 amp 2 EXTERNAL 1 INSERT SEND CLEAN FEED L R and AUX 1 amp 2 MONITOR 1 amp 2 0 1dB 0 1 5dB 10Hz to 20kHz 20Hz to 20kHz OdB OUTPUT 15dB OUTPUT lt 0 05 1kHz lt 0 3 DB 40Hz to 20kHz ILLUMINATES 15aB at the PRE FADER lt 70dB 40Hz to 15kHz INTERCHANNEL 8 INTERGROUP 28 NOISE MIC lt 126dBEIN 20Hz to 20kHz 200R SOURCE with respect to the input LINE gt 70dB SNR 20Hz to 20kHz EQUALISATION HF 10dB 10kHz VARIABLE SLOPE 15dB MAX 15kHz LF 10dB 100Hz VARIABLE TURNOVER 15dB MAX 30Hz MF 15dB PEAK 8 DIP RECIPROCAL Q 1 2 CENTRE FREQ 18dB 1k4Hz MFI 418dB 1k8Hz MF2 18dB 2k3Hz MF1 MF2 18dB 3k8Hz HPF 1 PRE TRANSFORMER 12dB OCTAVE 3dB 150Hz HPF 2 3dB 90Hz 12dB OCTAVE HPF 1 HPF 2 REFER TO CURVES OUTPUT LIMITER THRESHOLD 8dB RATIO 7 1 ATTACK 2 SETTINGS INTERNALLY SWITCHABLE 1 4ms 2 0 8ms RELEASE 2 SETTINGS INTERNALL SWITCHABLE 1 250ms 2 80ms MIC LINE LIMITER THRESHOLD 0dB RATIO 7 1 ATTACK COUNTER CLOCKWISE 0 5ms CLOCKWISE 10ms CENTRE 4ms RELEASE COUNTER CLOCKWISE 10ms CLOCKWISE 700ms CENTRE 300ms FACTORY SETTINGS FOR ATTACK AND RELEASE TIMES OUTPUT LIMITER SLOW MIC LINE LIMITER CENTRE CURRENT CONSUMPTION 8 INPUT 3
28. R IN XLR When driving the mixer from an external power source PIN 1 is the Ov connection and a voltage in the range 12V to 15V DC should be supplied to PIN 4 The power source should be capable of delivering approximately 400mA allowing some capacity for phantom powering If an external power supply unit PSU is to drive the mixer and simultaneously charge a set of NICADs a current capability of at least 650mA is required It is poor practice to run a PSU at its limit therefore we recommend a minimum of 750mA Audio Developments AD100 09 PSU is a suitable unit WARNING When NOT using the PSU AD100 09 supplied for the mixer ensure your 4 pin XLR is correctly wired to match the POWER IN connector Failure to do so may result in the breakdown of the internal DC DC converter Make this check even if using a PSU which may have been supplied to you in the past eg AD100 06 AD100 05 PSU is NOT suitable for use with an AD149 mixer and must not 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 Increasingly it is being reali
29. a 20dB attenuator pad thus degrading the signal to noise ratio to enable the amplifier to accept the full voltage range from a typical microphone 24 Now it is possible to produce a virtually overload proof input stage in which a pad is redundant and an external attenuator required only on very rare occasions With such an amplifier the gain control element can be placed in the ideal position ie the feedback loop ensuring the best possible noise performance we have just described AD149 s microphone amplifier Any audio mixing system is inevitably and at all stages a compromise between headroom signal to noise ratio dynamic range sensitivity We believe that we have achieved the state of SHIBUI Some boom microphone operators dislike wearing combination headsets preferring to use the boom microphone itself for talkback purposes In this case privacy is essential between boom operator and sound operator Once a module has been assigned to the boom microphone an internal DIL switch will guarantee the required privacy a private line This is a feature also available to a boom operator wearing the standard headset when a guaranteed private conversation between boom and mixer is required By a second internal DIL switch the boom microphone may be routed to the monitoring section for audition in isolation by external 1 and or external 2 without interfering with the sound mixer s requirements For a mixer of its type an
30. bars are available for the faders on adjacent modules rendering a stereo microphone module totally unnecessary All existing evidence indicates that a stereo module is an exercise in compromise a pair of mono modules with faders ganged for stereo operation will always offer more versatility and control but not one handed operation Personal experience tells us that ganged equalisation is rarely what is actually required in the L R domain and is NEVER required in the M S domain Ganged equalisation is also of necessity less sophisticated than that which it is possible to include in a mono module 26 All mixer inputs and outputs are electronically and mechanically suppressed against radio frequency interference 27 TECHNICAL SPECIFICATION ELECTRICAL REFERENCE MAX GAIN MAX INPUT LEVEL INPUT IMPEDANCE MIC POWERING MAX OUTPUT Odb 775mV at 1kHz unless otherwise stated MIC 80dB LINE 45aB MIC MAX GAIN 42aB MIN GAIN LINE MAX GAIN 7dB MIN GAIN STEREO RETURNS 18dB INSERT RETURN 18dB EXT 1 RETURN 18dB MIC gt 1k5R LINE gt 10kR STEREO RETURNS 250kR INSERT RETURN gt 10kR EXT 1 RETURN gt 100kR 48V PHANTOM amp 12V TONADER 24dBm 600R LOAD L R 0 24dB TRANSFORMER BAL 24dBm 600R LOAD 18dBm 600R LOAD 18dBm 600R LOAD AUX 182 TRANSFORMER BAL MONITOR 1 amp 2 UNBALANCED EXTERNAL 1 amp 2 UNBALANCED INSERT SEND UNBALANCED 18dBm 600R LOAD OUTPUT IMPEDANCE lt 60
31. coding or decoding The matrix amplifier adds and subtracts the M and the S signals after hard sums M S L and M S R If the positive lobe of the figure of eight microphone is to the right then M S R and M S L If these left and right signals are now added to derive the equivalent mono signal easy sums show that L R 2M If the matrix amplifier is used for this process then automatically L R 2S In other words an existing L R signal can be matrixed to M S and then subjected to any treatment which is applicable to M S signals manipulation of width of image and ambience etc for the FINAL L R presentation This is a very convenient way of effecting such changes on L R signals When using X Y techniques such changes have to be made by repositioning the microphone pair When the signal is in M S format traditionally if a tradition there be the stereo spread is controlled by varying the level of the S component A narrower spread is obtained by reducing the level of the S component Similarly the width is increased by increasing the S component This technique also has the effect of altering perspective and ambient content without affecting the mono signal A refinement of the method is to control the width by a balance control increasing S at the same time as decreasing M and vice versa This has the effect of maintaining overall level of the stereo signal To steer the output of an M S pair to any position within the final st
32. d size AD149 has an ultra sophisticated auxiliary section When sourced post fader and with level controls at maximum auxiliary signals are at the same level as and track with the main L R output from the module and are controlled by the channel fader In this case auxiliary outputs are available even when the L R output is switched off It is normal practice for auxiliary level controls to act only as attenuators but when sourced pre fader an extra 10dB gain is introduced into the auxiliary paths We believe this to be unique to AD149 An auxiliary stereo link converts auxiliary 1 level control into a master control for both paths and auxiliary 2 level control into a panpot across the auxiliary outputs from the module By combining the last two features AD149 can be configured not only as a four output 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 However if the mixer and recorder are connected via the insert points send AND return rather than the channel outputs clean feeds by selecting appropriate insert switches sample mixes may be auditioned at the time of production 25 For stereo operation linking
33. echniques 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 They possess an excellent low frequency response and although fairly immune to wind and blasting effects they are particularly adept at responding to traffic air conditioning plant and structure borne vibrations They provide a good sense of space and openness but for a given direct reverberant sound ratio they require the closest placement to the sound source They have the maximum potential for pickup of unwanted sounds although with minimum colouration When deciding upon an omnidirectional microphone there is a choice to be made between the type which is designed to have a flat response to an on axis signal direct or free field and the one designed to have a flat response to a reverberant sound field random incidence or diffuse field ie with an HF tip up in the on axis frequency response The MKH20 contains treble accentuation circuitry permitting usage in both direct and diffuse sound fields and also gives the microphone a directional effect at high frequencies THE MATRIX PROCESS Conventional left right stereo signals may be produced directly by using X Y techniques or indirectly by using M S techniques In the latter case the signals have to undergo a further process variously called matrixing en
34. er auxiliary points M signals may be mixed on AUX 1 and S signals on AUX 2 then matrixed to L R on the auxiliary outputs Alternatively a L R signal may be recorded from the main output and an M S signal from the auxiliary outputs Spot microphones would be added only to the AUX 1 mix When mixing in the L R domain and using one or more M S stereo microphones the panpots on M and S channels will be centred and the S switch 15 selected on the S channels to create a matrix across the M and S channels With CH 1 selected on the monitor module MON on the M channels will audition an M microphone on monitor 1 L amp R and headphones L 8 R outputs When setting up M S microphones the S channels may be monitored in the same manner BEFORE the S switch is selected After selecting the S switch the complete M S microphone may be monitored automatically in L R stereo At this stage the potential of these M S microphones may be checked by changing the M S relationship ie by varying the input gain of the S channels 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 61 Earlier we mentioned conflicting monitor requirements a problem arises when monitoring an S channel after its S switch has been selected In this case S would appear on MON left and S on MON right not very useful To overcome this difficulty swi
35. ereo 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 If the S signal is phase reversed the final presentation will be changed from L R to R L Reversing the phase of S is a useful technique if the orientation of an M S pair has been changed during a recording For example a boom may have been changed from an over the top position to an up and under position In a situation where several M S pairs cover the sound stage the S level control can be used to reduce to narrow stereo or even mono in times of trouble or when making difficult cross fades between pairs of microphones MATRIX AMPLIFIER WITH WIDTH CONTROL MATRIX AMP FIG 3 a If a mono signal is to be derived from fully modulated left and right signals simple addition will result in over modulation of the mono channel due to the increase in level caused by centrally situated signals Some manufacturers reduce this resultant level by 3dB and some by 6dB Mixing M S signals is a valid and very powerful technique particularly when matching sound to visual images A mono signal is directly available the stereo image can be made narrower or
36. eter VR2 adjusts the upper sector of the scale and VR3 adjusts the lower sector To initiate calibration set each preset to its mid position BBC scale using the tone generator and millivoltmeter as described above adjust mixer levels for a reading of OdBu on the millivoltmeter from a main output Switch the appropriate meter to the selected output and adjust VR1 for a reading of 4 Increase the output signal to 8dBu and adjust VR2 for a reading of 6 Decrease the output signal to 8dBu and adjust VR3 for a reading of 2 Repeat this procedure until an accurate set of readings is obtained without further adjustment to any of the presets being required Now check all points 1 to 7 on the scale to determine whether they are within specification N10 scale for a meter calibration of TEST OdBu With a main output signal of 6dBu adjust VR1 to give a meter reading at 6 Increase the signal to 6dBu and adjust VR2 to obtain a meter reading at 6 Lower the output signal to 18dBu and adjust VR3 to obtain a meter reading at 18 Repeat this procedure to obtain an accurate reading at each of these three points Now check the calibration of all meter points SDR scale with a main output signal level of 6dBu adjust VR1 to obtain a reading of 12 Increase the output signal to 6dBu and use VR2 to obtain a reading of 0 on the meter Lower the output signal to 18dBu and adjust VR3 to give a reading of 24 Repeat the procedure to obtain an acc
37. extra features that have been incorporated within AD149 by adopting minimum signal path topology and introducing circuit blocks only when required the mixer s noise performance has been maintained at the level achieved by AD146 Five modules are available any combination of input modules a microphone line b mono line c stereo line together with an output module and a monitor module only the latter two having dedicated positions within the frame The monitor module is based on the one proved and approved in AD146 the first four output mixer in the 140 series The order of selector switches has been changed to simplify the process of A B comparisons between sends and returns to and from the recorder By popular request each stereo return has been fitted with a calibration preset A second EXTERNAL circuit has been included for use by a director producer and monitoring capabilities available to both external circuits have been increased A master safety switch has been added to the communications circuitry making accidents very unlikely 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 post production 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 When designing AD14
38. fter the microphone amplifier for correct and predictable combining of the two filters when selected simultaneously Operating frequencies are to be found in the TECHNICAL SPECIFICATION as are all parameter details High pass filter HPF 2 operates independently of the equaliser To control the gain of the input amplifier a limiter may be switched into circuit 17 limiting action being indicated by LED 22 Limiter release time 23 attack time 24 and threshold 25 may be adjusted externally factory settings and values at the clockwise and counter clockwise positions of the presets are detailed in the TECHNICAL SPECIFICATION Despite the limiter on the input amplifier overload can still occur in later stages The limiter also operates on a line input On the mother board a DIL switch will be found between module positions 1 2 3 4 etc When selected to right the DIL switch will link the limiters of the pair of modules for stereo operation The presets of each module should have the same settings for perfect parallel tracking The mixer is supplied with the modules unlinked All limiter link DIL switches are accessed by removal of the back panel covering the mother board There is no requirement to remove input modules It is ESSENTIAL that X M L signals are inserted in odd numbered channels and that Y S R signals are inserted in the even numbered channel ABOVE Following the microphone amplifier is the equaliser swi
39. h out of phase images can occur when using non coincidental microphones shuffling should be restricted to frequencies below about 300Hz ie to frequencies which arrive in phase at both microphones 19 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 As may be appreciated shuffling is an extremely versatile technique but its effects are largely unpredictable therefore each recording must be treated on its own merits Shuffling as described takes place at low frequencies and has no effect at high frequencies audible noise is not increased which is not the case with simple overall width increase If shuffling techniques are to be used during post production the monitoring system must be optimised for precise stereo imaging This effectively eliminates many of the loudspeakers used as studio monitors MATRIX AMPLIFIER WITH WIDTH AND POSITION CONTROLS AND SHUFFLER WIDTH SHUFFLER MATRIX AMP POSITION BALANCE STEER 20 FURTHER READING British Patent Specification 394 325 AD Blumlein Improvements in and relating to So
40. he left and right outputs of the matrix Thus if an M S microphone is set up with incorrect orientation of the S microphone 41 changing phase of the S microphone channel will rectify the situation without having to disturb the microphone But see also M S NOTES 42 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 in place signal MON is independent of L R routeing 16 and is derived from the output of the panpot and S switch 15 if selected Pre fader listen 19 with its LED indicator 20 is a third way of aurally monitoring the module The overload LED 21 illuminates 3dB before clipping at the input to the fader The Penny amp Giles fader 34 is calibrated 10dB down from its fully open position allowing the operator to work with 10dB of gain in reserve Faders on adjacent modules can be coupled for stereo operation by the use of standard ganging clips 43 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 bo
41. hoice of type and position for the M microphone the optimum mono signal can be achieved with a minimum of off axis colouration Of all stereo recording techniques M S is the one that offers the engineer the most control and flexibility not only during recording but also during post production By varying the ratio of the signals sent to the matrix amplifier the width of the stereo image can be adjusted By changing the pickup pattern of the M microphone a remotely controlled polar response being advantageous in this context the apparent distance from the sound source and hence the amount of ambient information in the M signal can be controlled The most popular choice for the M signal is a cardioid microphone In this case after matrixing the two signals the resultant left right stereo is equivalent to an X Y pair of hypercardioid microphones The cardioid is the only M microphone which does not encode rear sounds as front sounds overall pickup from the rear being low Angular distortion is low over the pickup angle and there is uniform directional encoding of reverberation If an omnidirectional microphone is used for the M signal the X Y equivalent is a pair of back to back cardioid microphones with their common axis parallel to the axis of the figure of eight microphone This arrangement is useful when performers can be arranged on both sides of the microphone pair If a figure of eight microphone is used for the M signal the X Y equ
42. ible via the internal preset RIGHT HAND PRINTED CIRCUIT BOARD TO CHANGE IDENT TONE TO RIGHT OUTPUT S1 gt x Se p MARKER zo Remove through pin TONE is SENS 51 K COMPONENT SIDE VIEW R45 Remove through pin from Y2 as indicated Cut track between X2 and VI Add link between X1 and X2 Add link between Y1 and Y2 NOTE Only make connection to component side pad of Y2 eI FIG 13 49 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 Refer to FIG 13 The remote stop start facility is accessed via the D connector SUB 1 Pin 3 normally closed Pin 4 common Pin 5 normally open Some recorders require a pair of contacts to be opened in which case use pins 4 amp 3 and some require a pair of contacts to be closed in which case use pins 4 8 5 NOTE 1 A common timing circuit is used for interrupted line up tone and remote marker tone It is recommended therefore that the interrupt button INT 14 is not operated during recording 2 Care should be taken when wiring the REMOTE at the D connector There are two conventions in use one for the common wire
43. inuous or interrupted 15 Line up tone to L R ou 16 Line up tone to auxiliar outputs 17 Aux outputs matrix 20 Aux 1 master control 21 Aux 2 master control 23 Aux stereo link 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 PEL right by use of switches 10 11 12 When no switch is selected meters read main L R output thereafter switch 11 overrides switch 10 and switch 12 overrides switches 10 and 11 Switch 11 reads the signal entering monitor 1 path a signal that can be either in the L R domain or in the M S domain Battery status is read on the upper meter by BATT 8 and the meters may be illuminated by ILL 9 overuse of this function will rapidly drain the batteries When the voltage drops below a safe operating level the MIX ON indicator LED 7 will flash Output signals to be metered follow output faders matrix amplifiers and limiters When the auxiliary paths are being used as a stereo pair their output potentiometers 20 and 21 may be linked 23 for one handed operation AUX 2 becoming the stereo master A matrix amplifier may be inserted across auxiliary 1 and 2 outputs MTX 1
44. ivalent is a crossed pair of figures of eight each being at 45 to the central axis of the sound source Of all M S techniques this form provides the most even distribution of reverberant pickup 11 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 gt 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 When M lt S M omnidirectional the resultant cardioids become more hypercardioid M cardioid the rear lobes of the resultant hypercardioids are increased in size and the included angle increases M figure of eight the included angle between the resultant crossed pair is greater than 90 All things being equal which of course they never are once an MS pair has been installed varying the input gain of the S channel will not only alter the width of the resultant L R presentation but also effect changes as outlined in the above table Whereas if an X Y pair is being used changes would involve physical manipulation alterations to included angle to position or replacement with a different type of microphone Refer to FIG 2 12 M S X Y TRANSFORMATIONS M S T U Il gt x
45. ly 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 FUSES External Battery DC Supply Supply Limiter threshold is set at the factory at 8dBu PPM 6 but an internal preset potentiometer allows adjustment to any other level above OdBu The limiters are to be found on the left hand PCB of the output module LH output ident as an alternative to continuous tone on both left and right outputs and AUX 1 2 outputs the LH and AUX 1 outputs can be pulsed with tone for three seconds Microphone powering the mixer will remain unconditionally stable if the powering on unterminated input channels is switched off this also improves the noise performance and crosstalk Powering 48V phantom or 12V tonader may be selected before or after the microphone is connected to the module Module fix screws Hexagon head screws are used to fix the modules and back cover The size being 1 5mm HEX A F with a 2 5M thread If it becomes necessary to remove modules or back cover it is strongly advised using a good quality hexagonal head driver Use of a screwdriver however desperate is not recommended Surfaces every working surface is covered by a hard plastic membrane which is printed on the reverse side These surfaces may be cleaned by most solvents and without fear of the legends being erased
46. ng the monitor BAL control 11 hard left and select MONO 14 thus isolating the in phase signal from the S channel Alternatively and if the engineer has requested a restricted swing on the BAL control 11 selecting either of the MTX switches and MONO 14 will achieve the same result When mixing in the M S domain M channels will be panned hard left and S channels will be panned hard right Spot microphones will be panned left to mix with M channels only Any X microphone will be panned centre and any Y microphone will be panned centre and have its S switch 15 selected thus converting the X Y microphone to the M S domain MON on an M channel will audition the M signal on monitor 1 left output and MON on an S channel will audition the S signal on monitor 1 right output By selecting MONO 14 on the monitor module each of these signals will appear on monitor 1 left and right outputs If the M and S channels are selected simultaneously to MON the resultant M S signal is incomprehensible but can be converted to the L R domain by selecting MTX 2 13 on the monitor module By using the monitor BAL control 11 this L R signal can now have its width changed and potential realised without changing channel settings An M S main mix may be matrixed to the L R domain for the final output from the mixer by MTX 6 on the output module before any final limiting When mixing in the L R domain without M S microphones X Y A B microphones
47. nt 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 OdBu at pin 101 indicated on FIG 6 Turn SET O preset counter clockwise until the reading at pin 101 reduces by not more than 0 2dB Increase input gain control 27 for a reading of 1dBu at pin 101 and switch in the limiter 17 Turn the threshold control until the reading at pin 101 is reduced to OdBu atwhich point the limiter LED 22 should illuminate This is the setting requested by customers leaving 18dB before clipping within the channel We believe that this setting is over cautious and unfortunately destroys input headroom which the limiter is actually intended to protect The range on the threshold preset is 5dBu ccw to 15dBu cw If set at 15dBu the limiter and overload LEDs would operate together For optimum use of the limiter we suggest it be set at 12dBu ie 6dB before clipping The DC voltages on IC10 should be approximately 2 6V at pin 10 and 2 0V at pin 12 ie a difference of 0 6V 45 BLOCK DIAGRAM PART 2 T ans 134 TIXI A WALNOD dad A 2MS 11d TMS qd SIRI woe T NOW J
48. ny sound engineers have experienced the power of FLEX EQ our industrial strength equaliser and wish to be able to use it when making original recordings 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 tribute to and celebration of the genius of Alan Blumlein 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 We d reckoned however without the persistence nay insistence of our customers for a mains operated version of the AD146 with four auxiliaries we ve called it AD144 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 Visual Inspection Identification please make a separate note of the serial number for your own capital equipment records Ensure that it agrees with the number on the invoice packing note The
49. of 10dB but film sound recordists have always had their own particular method of working and in order to guarantee the capture of everything from Blow winds and crack your cheeks rage blow to the merest zephyr they open channel faders to maximum and perform any active mixing on the input gain controls This maximises the dynamic range of the input amplifier but throws away the aforementioned safety net in the process Unfortunately it also reduces headroom later in the signal path and ensures a less than optimum signal to noise ratio It also seems to negate the raison d tre for the linear fader To accommodate alternative operating methods we have replaced our usual switched input gain control with a potentiometer and added an additional safety net in the form of a limiter controlling the gain of the input amplifier ALC This limiter has however a more important r le 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 Once upon a time it was possible to achieve a gain swing of only 30dB in the input stage necessitating the introduction of
50. oltage at PIN 10 of IC 1 should be approximately 0 6V different from that at PIN 12 The right output can be set using the above procedure but the preset and IC numbers change to correspond with the output being calibrated The link function has no individual setting of its own To ensure this works within specification it is important that L and R outputs are set up as a pair After following the above procedure the DC voltages at PINS 10 and PINS 12 of the ICs should be identical Tolerance 0 05V with typical figures at PIN 10 of 2 6V and PIN 12 of 2 0V There are two DIL switches associated with the attack and release times one for the left output the other for the right output 53 THIS PAGE IS BLANK 54 MONITOR MODULE 1 Channels to monitor 2 L output to monitor 3 R output to monitor 4 L R output to monitor 5 Stereo return to monitor 6 Aux 1 output to monitor 7 Aux 2 output to monitor 8 Aux 1 2 output to monitor 9 Stereo return 2 to monitor 10 Monitor 1 output level control 11 Monitor 1 balance 12 Monitor 1 output dim 13 Matrix 2 14 Mono of monitor 1 15 Monitor 2 output level control 16 PFL level control 17 Talk to External 1 circuit 18 Talk to L R output 19 Talk to Aux 1 amp 2 outputs At MONITOR O CH em OR OL 2 Openi CO aux 1 C aux 2 AUX STEREO 0 ZA o EXT2 COMMS
51. om 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 PRIVATE LINE It has come to our attention that many boom operators dislike having a personal microphone attached to their headset instead they prefer to use the boom microphone itself for communication with the sound mixer This of course precludes conversation during programme Under this system complete privacy must be guaranteed To create a private line between boom operator and mixer DIL switch 3 on the main PCB of the boom microphone module should have its slider moved downwards This does not interfere with normal operation of the module At the end of a take pressing S 15 S Safety isolates the boom microphone from all sections of the mixer except the operator s headphones jack and GUARANTEES COMPLETE PRIVACY of communication between EXTERNAL 1 and sound operator MIC LINE MODULE PCBs Note By request DIL switch 3 is now fitted to only one module The mixer is despatched from the factory with this module installed in position 1 in the chassis with the facility set ON The module may of course be placed in any other position in the chassis DIL 1 E UE j pl L 44 LIMITER CALIBRATION Refer to page 49 1 for use of external test equipme
52. ompare the vitality of the M mono mix from the M S domain with the dull and rather lifeless mix from L R MONO If a stereo line module is available creation of a Blumlein Loop will allow both the effect of phase inversion on the S signal and the differential application of equalisation within the M S domain to be appreciated Refer to page 11 2 and 3 64 MOTHER BOARD 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 PCB EXT 1 CH MON DIL SWITCHES DIL 2 DIL 3 DIL 1 DIL 3 bypass DIL 1 EXT 1 R talk monitor DIL 2 65 Link Pre fader Select Select Pre fader Fast Slow Fast Slow Disable Disable MON 1 Enable LTL T 11 on off on off 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 110V 120V AC source or a 220V 240V AC source Ensure that the AC Voltage Selector Switch on the front panel is in the correct po
53. on external 1 output Selected by DIL switch 1 on the right hand PCB of the monitor module there is a choice of two signals a a mono mixdown of the signal appearing on monitor 1 output In view of the fact that during production the sound operator is more likely to be interested in PFL monitor 1 output may be customised to the boom operator s requirements probably the main output so that he may audition his microphone within the overall context This will probably also satisfy the sound operator s requirements monitoring the final mix together with PFL override b the same signals that are available to external 2 but independently and externally selected There is a choice CHS MON 27 between MON as a above and CHS which is a mono mix of all channels selected to MON but WITHOUT CH 1 necessarily being selected Refer to FIG 16 In the case of external 1 BOOM 1 28 will override the selection made on CHS MON 27 and route the boom microphone to the operator s headset In the case of external 2 BOOM 2 26 will override the selection made on CHS MON 27 and route the boom microphone to the director s producer s headphones This facility must already have been selected on the boom microphone module Refer to microphone line module section External 1 has the additional capability of its own split monitor selected by DIL switch 2 on the right hand PCB of the monitor module Whenever communication is taking place f
54. onal standard sic AD149 is supplied with interrupted tone on the left hand output but can easily be changed by the end user to the more logical right hand output 23 The input modules have features new to the AD140 series of mixers several of which are unique to Audio Developments many being taken from our list of customers suggestions In particular we have been able to accommodate the requirements of film sound recordists and for non European methods of working Whilst electronic components continue to shrink in size mechanical components and human fingers steadfastly refuse so to do Throughout the AD140 series reducing the size of modules has also reduced the panel area available for connectors We know that connectors mounted on side panels are totally unacceptable so when insert points were demanded the only possible position for the jack was at the top of the module fascia at least this makes it possible to dress insert cables along with their input and output counterparts Clean feeds may be switched pre or post fader and we are assured that they will only be used when recording from microphones enabling usage of the second module connector for channel output The highly acclaimed discreet and discrete transformer balanced microphone amplifier designed for AD146 has been incorporated into AD149 s microphone line module Under normal circumstances the channel fader operates around the zero mark giving a safety net
55. ow frequencies are often narrower than those at high frequencies In view of the narrowness of the angle subtended by a TV or cinema screen at a typical viewing position Why stereo is a question frequently asked Why not is the reply more frequently being given even stereo dialogue is becoming increasingly common Advantages of stereo include a more accurate portrayal of the local acoustic separation of voices with space and air between them correct placement and perspective of locally occurring sounds and sound effects 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 There is a choice of capsules available when using this crossed pair or X Y technique The earliest of these techniques were developed by Blumlein ONE of his techniques uses a pair of figure of eight microphones set at an included angle of 90 Best used in large spaces where reflections from boundary surfaces are minimal and where strong signals are not presented to the rear quadrants this technique produces a very natural sound When cardioid or hype
56. r 1 output jack socket Monitor 2 output jack socket SEISJE 32 a 4D 43 44 gt 10 13 10 Left Right output return multiway 11 Left Right output return connector unbalanced 12 Auxiliary output return connector unbalanced Auxiliary output return multiway Off On switch external 8 internal External DC power input Subsidiary connector Talk send 8 return DC power output 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 8 Outputs Pin 1 Shield Pin 2 Signal Pin 3 Signal In the case of an unbalanced line inputs and outputs pins 1 amp 3 should be connected This will not lead to a loss of level When the option of separate connectors for microphone and line has been selected the channel output clean feed signal appears on a mono unbalanced jack in the centre of connector 2 otherwise connector 2 carries channel output Main 3 and auxiliary 4 outputs are transformer balanced and are at line level The unbalanced stereo returns enter the mixer on two standard A type unbalanced stereo jacks L R 5 and AUX 6 Unbalanced monitor 1 output is on a mono unbalanced A
57. rcardioid microphones are used the included angle is usually 90 120 Some authors reserve the term X Y to refer only to a crossed pair of cardioid microphones The included angle determines the width of the stereo image and is selected with other factors in mind distance from and width of the sound source and polar response of the chosen microphones The polar and frequency responses together with sensitivities should be matched as closely as possible otherwise considerable colouration and image shift can occur with changes in pitch When cardioid capsules are used they are usually placed fairly close to the sound source giving a high ratio between direct and reverberant sound and good rejection of unwanted sound at the rear of the microphone pair This means that in TV recording the microphone appears on camera A longer range system is required for picking up dialogue in drama etc Even listeners in stereo will have difficulty with text if an X Y pair is set out of sight and probably with neither microphone pointing directly at the sound source Even with an optimally positioned X Y pair of cardioid microphones there is no guarantee that the resultant recording will fill the space between the loudspeakers Post production techniques are available to overcome this and other problems but experience has shown that to take advantage of these techniques the capsules should be CROSSED OVER and spaced apart at a distance of approximately 50 mm
58. rom mixer to external 1 the monitor signal remains on the right earpiece and communication appears on the left earpiece Refer to FIG 16 59 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 The level of the internal microphone is controlled by preset 31 Communication from EXT 1 to the sound operator is initiated at the outstation and feeds the PFL mix busses Like other PFL signals it is under logic control and replaces any other signal on monitor 2 output ie the operator s headphones The level of this return signal is controlled by potentiometer PFL 16 Toa TALK to L R TAK fo AUX 1 2 LE FIG 16 INTERNAL MC K gt CHAMON 300M 2 L CHs MON MOND gt SNS kas BTI MON 1 OP MOND gt FROM BOOM MIC 60 MIXING 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 Refer to
59. rom 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 This is non destructive SIP solo in place usage of the monitor 1 path rather than destructive in the recording studio sense A mix different from the main mix may be set up on the monitor 1 path using CH 1 only and independent of the L R channel routeing This could be a mix minus The identical contribution of any channel to both the mix minus or monitor mix and main output will be controlled by the channel fader The output from monitor 1 path and to monitor 2 output is controlled by ganged potentiometer 10 It is now possible to insert a Blumlein Loop into monitor 1 path MTX 1 23 MTX 2 13 with a zero to zero balance width control 11 between the two matrix amplifiers When the balance control is fully counter clockwise L only the LH signal appears on monitor 1 amp 2 outputs Similarly when fully clockwise R only the RH signal appears on monitor 1 amp 2 outputs Selecting MONO 14 will place these LH amp RH signals on both sides of monitor 1 amp 2 outputs thus can PFL be isolated on monitor 1 output when SPLIT 22 is selected See last this page The balance control may also be used to compensate for an off centre position when monitoring on loudspeakers At ANY TIME during recording or post
60. section may be used to achieve the required result ADO66 13 FLEX EQ is such a filter set This equaliser also satisfies a further requirement the transition to the equalised part of the frequency spectrum should be as gentle and smooth as possible The skirts of the FLEX EQ low Q filters are of the order of 6dB per octave Shuffling is too powerful and complex a technique to cover adequately in these application notes but it is worthwhile listing some of the situations in which the technique will be advantageous Black records become easier to cut and reproduce when the width is reduced at low frequencies FM stereo reception noise can be reduced by reducing the width around 7kHz Reduction of low frequencies in the S channel helps to eliminate structure borne vibrations Increasing the width at low frequencies will bring into coincidence high and low frequency components of an image which have become separated because of imperfections in microphone polar patterns eg where cardioid microphones become more omnidirectional at low frequencies Dryness and lack of spaciousness are inherent in recordings made with coincident cardioid microphones The sense of space can be improved by increasing the difference signal below about 700Hz This can also lead to an improvement in stereo imaging away from the stereo seat When shuffling techniques are applied to recordings made with near coincident microphone techniques or techniques in whic
61. sed that of the coincident microphone techniques the rediscovered M S middle side technique has many advantages over the other coincident techniques particularly when working in unknown or difficult situations Several leading manufacturers are now producing integrated M S microphones but many are of the electret variety exhibiting typical frequency response aberrations Our own extensive research and experimentation have shown that the highest quality and maximum flexibility are obtained when using the new generation of discrete true condenser microphones An extremely high quality M S system can for instance be assembled from the new SENNHEISER range of studio condenser microphones MKH20 30 40 50 60 70 together with the MZD30 which clips two microphones together in piggy back style and aligns the capsules in the same plane It should be noted that these microphones use RF technology and therefore offer high immunity to moisture in the atmosphere With such a system not only can the most suitable choice be made for the M signal microphone omnidirectional cardioid hypercardioid short gun long gun but also there is no requirement for extra microphone powering units and or matrix amplifiers as AD149 is able to supply all the control necessary for professional stereophonic recording and post production For stereo TV and film M S is the obvious choice it permits the easy matching of audio and visual images focusing performers
62. serial number label is on the back cover adjacent to the battery compartment Configuration check that the correct number and combination of input modules have been installed If for any reason you wish to change the positions of the modules do not do so until after completion of any acceptance tests Any tests then made will be to a known configuration and can be compared with our factory records Temperature check the meter glasses for condensation If the package has been in transit during cold weather leave the mixer for at least 12 hours to allow it to return to normal room temperature Any measurements or subjective tests then made will be to a known temperature reference Specific Points Battery compartment the mixer has an integral battery compartment to accept 10 size C cells and is formed as part of the bottom transversal extrusion This helps to lower the centre of gravity as well as adding to the rigidity of the frame DC DC converter is mounted on the top side of the battery housing and is underneath the fader section of the output and last four input modules In order to facilitate the testing and calibration of all modules a set of two extender modules is available from the factory Connectors for convenience the connector panel is labelled for reading from above All connectors are in line with their corresponding module Fuses to protect the mixer and internal power supply are mounted on the power supp
63. sition for the source in use Operating the equipment at the wrong voltage could be hazardous Care must be taken to connect the LIVE NEUTRAL and EARTH pins of the PSU s IEC mains connector to the corresponding terminals associated with the AC source The ON OFF switch contains an indicator that illuminates when the PSU is operational FOR SAFETY REASONS AD100 09 POWER SUPPLY UNIT MUST BE CONNECTED TO MAINS EARTH Any maintenance to the PSU or its mains cable assembly should be performed by a qualified engineer CHARGING If nickel cadmium cells are fitted in an AD140 series mixer they may be recharged in situ from AD100 09 power supply whether the mixer is in use or not Maximum current is set at 250mA in addition to the 500mA of current supplying the audio electronics The charging circuit has its own ON OFF slide switch and LED indicator DO NOT ACTIVATE THE CHARGE CIRCUIT UNLESS THE MIXER IS FITTED WITH NICKEL CADMIUM CELLS FUSES Two 20mm ANTI SURGE fuses protect AD100 09 against fault conditions Should either fail it is strongly recommended that the cause be traced Refer to the TECHNICAL LIBRARY Only suitably qualified personnel should service the power supply unit The fuse holder on the front panel contains the mains fuse 250mA HRC TYPE T 240V AC For continued safety the specified fuse link must be fitted in the mains fuse holder when a replacement is required Ensure it is of a type approved by a National Approved
64. t is independent of the channel mute 16 When sourced pre fader an additional 10dB gain is available in the auxiliary signal paths when the level controls are set to their calibration dots When the channel fader is on its calibration mark auxiliaries may be switched between pre and post fader without any change in signal level The auxiliary stereo link ST 14 configures the two auxiliary paths as a stereo pair the auxiliary 1 level control becomes the master gain potentiometer and the auxiliary 2 level control pans the module signal between auxiliary 1 and 2 outputs When in stereo mode switch 11 is the source selector switch 13 being redundant Thus post equaliser and with auxiliary 1 sourced pre fader AD149 is two independent stereo mixers in one chassis where auxiliary 1 level control effectively becomes a second channel fader with a gain reservoir of 10dB The unbalanced post fader channel output or clean feed is available from CONN 2 By special request the mixer may be fitted with separate connectors for microphone and line inputs In this case the channel output will appear on the jack in the centre of the LINE input connector The channel output can be selected to pre fader via DIL switch 2 on the main PCB S 15 enables a matrix amplifier to be created across adjacent pairs of input modules This feature receives in depth treatment elsewhere in the manual Changing the phase of an S signal swaps over t
65. tch 2 selects the main left output from the mixer to monitor 1 8 2 left and right outputs Switch 3 selects the main right output from the mixer to monitor 1 8 2 left and right outputs Switch 4 selects the main stereo output from the mixer to monitor 1 8 2 MONO 14 mixes any two channel signal appearing on monitor 1 path and presents it to both left and right outputs of monitor 1 in this case a mono mixdown of the main output from the mixer L R 2 3 produces the same result Switch 5 routes the calibrated 20 stereo return 1 to monitor 1 8 2 The return will probably be the signal from the playback head of the tape recorder By alternating adjacent switches 4 and 5 A B comparisons to and from tape may be made Stereo return 2 9 with its calibration control 21 is identical with stereo return 1 Stereo return 1 is also called L R return and stereo return 2 is also called auxiliary return Switches 6 7 8 provide the same functions for the auxiliaries as switches 2 3 4 do for the main mixer output Signals for output monitoring are taken from the final mixer outputs ie after the faders output matrix amplifiers and limiters 56 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 f
66. tch 9 Within the equaliser it is possible to select 7 and or 8 four frequencies for the peak dip mid frequency band Because of the inherent inaccuracy of the centre detent mechanism it is not Audio Developments practice to fit such devices to equaliser amplitude controls HF 28 MF 29 LF 30 40 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 pre fader channel signal is always present on the jack TIP Thus at all times two output signals are available from the module pre fader from the insert point and post or pre fader from the clean feed A possible and unusual usage during production has already been detailed on page 25 The two auxiliary paths have a common ON switch 12 but each path has its own pre or post fader source selector 11 and 13 The level controls 31 and 32 are scaled from oo to 10 with a calibration mark at zero If sourced post fader the level control acts as an attenuator and when at maximum auxiliary signals track with and are at the same level as the module s main output L R Under no circumstances does auxiliary operation depend upon channel routeing ie i
67. techniques to this end facilities have been incorporated to take advantage of these techniques The result is AD146 a four output mixer This was followed by AD148 edit mixer Based on AD146 two comprehensive left and right monitor modules have been added for editing purposes If a mic line module is included for commentary or voice over purposes its input gain switch can be changed to a potentiometer and its gain structure changed to ensure consistent level matching with a fixed mechanical point of reference Unfortunately this way of working does reduce headroom and also compromises a mixer s noise performance After AD146 AD148 it was back to the drawing board Our customers were still demanding a two output mixer Despite past assurances to the contrary T powering is still required And could we incorporate auxiliaries And could we possibly bring it to market at entry level We have and we have and that s MERCURY AD147 AD149 completes the 140 series of mixers and has a repertoire of party tricks not to be found in any other mixer not even for ready money The design team took as its starting point our list of all the ideas and suggestions presented to us over the past few years Many of these requests came from film sound recordists a sub set of recordists we have unintentionally neglected in the past Since the days of R amp D for AD146 channel insert points suddenly became de rigueur lIt transpires that ma
68. tioned in three ways a PFL pre fader listen b AFL after fader listen c SIP solo in place non destructive The output module is almost identical with the one designed for AD146 but with simplified meter switching At rest the meters read L R output but this can be overridden in turn by auxiliary 1 8 2 outputs monitor 1 output and stereo PFL Attack and release times of the main output limiters may be selected on DIL switches on the module s left hand PCB A matrix amplifier see M S NOTES may be inserted in the main L R output and across auxiliary 1 amp 2 outputs By request auxiliary masters are potentiometers rather than faders but we have included a link switch so that they may be operated as a stereo pair 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 When designing AD146 we asked our customers on which side they would prefer interrupted pulsed line up tone logically and unanimously the right hand output was requested Since that time we have been accused of attempting to create a new standard but have yet to receive a request for line up tone to the suggested new internati
69. trol 28 High frequency control 29 Mid frequency control 30 Low frequency control 31 Auxiliary 1 level control 32 Auxiliary 2 level control 33 Panoramic potentiometer 34 Channel fader LIM LINK o PRIVATE LINE CLEAN FEE 300M L gt R gt MONIL gt MONIR 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 When switched to line input 3 no damage will occur to external equipment should microphone powering remain selected momentarily Such is the isolation a microphone and line level input may remain connected simultaneously when separate input connectors are employed Phase change 4 is pre transformer and operates on both microphone and line inputs The first high pass filter 5 is pre transformer and likewise operates on both microphone and line inputs In this position the high pass filter protects the transformer from low frequency saturation caused by wind traffic air conditioning etc The second high pass filter 6 is placed a
70. und transmission Sound recording and Sound reproducing systems British Patent Specification 780 337 PB Vanderlyn Improvements in or relating to Binaural Sound Transmission Systems British Patent Specification 781 187 PB Vanderlyn Improvements in or relating to Electrical Sound Transmission Systems Stereo Shuffling New Approach Old Technique Michael Gerzon Studio Sound July 1986 Applications of Blumlein Shuffling to Stereo Microphone Techniques Michael Gerzon J Audio Eng Soc Vol 42 No 6 In later sections we refer to the creation of a Blumlein Loop This is a section of signal path in the M S domain in which Blumlein s techniques may be applied 21 AD149 AUDIO MIXER Audio Developments has for more than 25 years set the standards for portable audio mixers With AD149 we have created a new standard for the twenty first century by offering potential and a degree of sophistication together with a simplicity never previously encountered in a mixer of its type or size we have created a product worthy to stand alongside and be used with FLEX EQ the world s most powerful equaliser AD149 is equally at home with its handle attached in a studio console or in a post production editing suite and is available powered either by internal batteries or mains only In both cases a suitable mains power supply is available for the mixer AD146 was designed to be a discreet and supremely quiet mixer Despite all the
71. urate reading at each of these three points Now check the calibration of all meter points 92 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 Issue 4 does not indicate an early improvement in circuitry simply a change in layout to make testing simpler With no signal present VR1 should be adjusted to give a reading in the range 1 5V to 2 5V at PIN 12 of IC 1 VR2 should be adjusted to give a reading in the range 2 5V to 3 5V at PIN 10 of IC 1 Apply a signal at 1kHz to the mixer to give a level of OdBu at L output Then select the limiter function and adjust VR1 until the output signal starts to fall typically 0 2dB The DC voltage at PIN 12 of IC 1 should be approximately 2 0V After setting VR1 adjust the output signal to just greater than 8dBu with the limiter deselected Introduce the limiter and adjust VR2 until the output signal falls to 8dBu This is the THRESHOLD setting If a different threshold setting is required alter the signal levels accordingly The DC v

AD149 - Zeigermann

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