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Model 750 - Studio Technologies, Inc.

1. SIGNAL x PRESENT PEAK DETECT Auer BUFFER as AMPLIFIER AMPLIFIER INVERTING t 21 W 150 5K GAIN 0 TO 28dB GAIN 0 TO 2808 BUFFER AM AM cg mt AUX 1 48V we 2 ax Ze s im ee um ve ea Marin oj ge INPUT 3 power E XLR F 1 Ke l AM AM AM gt AUX MIX R m f ki 1 f 1 1 He Lu ENEE 2j AUX ACTIVE OUT NORMAL MIC pesi 1 i So 1 48V OF Fee l SV MAIN mwen VV EE n Nes LINE Lou POLARITY INVERT v av 05 MIX L AM gt MAIN MIX R BALANCED SUMMING LINE DRIVER BUFFER CONFIGURABLE Ge t 21 DP 1 25 MAN OUT L OUTPUT gt 1 4 3 COND 4dBu DIP 2 E21 MAIN OUT R K 48V gt 4 C2 Aux OUT L Sides 15V gt es 4 02 Aux OUT L DIP 5 EY 1 2 DIRECT OUT AW 75080 C STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER MIC LINE INPUT CARD LOCATED ON BACK PANEL BLOCK DIAGRAM LOCATED ON FRONT PANEL POLARITY VS INPUT NOMINAL LEVEL IN dBul DRAWING NO DATE PAGE 30600 11 20 96 01 or 07 BI COLOR LED E s BI COLOR LED 20
2. SIGNAL SIGNAL PRESENT PRESENT PEAK PEAK DETECT DETECT A DIFFERENTIAL t 1 INPUT SUMMING Y BUFFER BUFFER BUFFER i 2 2 2 121 LEFT 5 e AE Ug AUX XLR F pou T 1 m queue gt joe i i T AW gt AUX MIX R STEREO LINE INPUT IN L TO OUT Rex 4dBu Pie J k AUX ACTIVE 2 l RIGHT XLR F 3 E IN R TO OUT 1 x MAIN IN R TO OUT R 4 n p m gt MAN uit de ui w gt MAIN MIX R BALANCED LINE DRIVER 2 1 2 LEFT e MAIN OUT L 1 4 3 COND a MAIN OUT R MAIN OUTPUT 1 OR 2 4dBu RIGHT m mar 1 4 3 COND L 18V d 15v gt LOCATED ON BACK PANEL LOCATED ON FRONT PANEL POLARITY VS INPUT NOMINAL LEVEL IN dBul b STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER STEREO LINE INPUT CARD BLOCK DIAGRAM DRAWING NO DATE 11 20 96 30600 PAGE 02 or 07 DIFFERENTIAL INPUT BUFFER REC TB EXT AUDIO INPUT 1 4 3 COND 20 TO 4 VEL TRIM BUFFER t 20 t 81 201 INTERNAL MIC a gt REC TB AUDIO INVERTER Y TB TO SETUP DIRECT OUT
3. SUMMING SUMMING BALANCED BUFFER BUFFER LINE DRIVER i VOICE REC PLAY 2 2 LEFT AW 1 4 3 COND v L R F Lr Fwa TRIM REC MCU L ONLY FN SETUP DIRECT OUTPUT Fa 4dBu R ONLY 5 4 n RIGHT t t w 1 4 3 COND SINE WAVE m T e gt GENERATOR VOICE PLAY 4 me 3 v AUX w SINGLE TONE Lou W gt AUX MIX L 1 MULTI Lo Dann D TONE J 7 AW AUX MIX R 1 HESS NS REC TB AUDIO SOURCE EXT INT DIP 1 REC L R DISABLE ENABLE DIP 2 T AUX ACTIVE REC L ONLY R ONLY DISABLE ENABLE DIP 3 SINGLE TONE 400Hz 1kHz DIP 4 MULTI TONE SEQUENCE BASIC ADVANCED DIP 5 x MAIN v AW MAIN MIX L ati NW MAIN MIX R gt MIC ACTIVE 15V gt sy n quu 007 mw SUPPLY IV a OUT nay STUDIO TECHNOLOGIES INC I MODEL 750 AUDIO MIXER SETUP CARD LOCATED ON BACK PANEL BLOCK DIAGRAM LOCATED ON FRONT PANEL NOMINAL LEVEL IN dBu DRAWING NO DATE PAGE 30600 11 20 96 03 or 07 MAIN MIX L MAIN MIX R AUX MIX L AUX MIX R TB TO SETUP DIRECT OUT
4. ze TB TO SETUP DIRECT OUT i si gt MIC ACTIVE 1 8 REC TB AUDIO TB TO MAIN amp AUX OUT i 0 v LIMITER COMPRESSOR SUMMING ACTIVE BUFFER BUFFER LINE DRIVER t 21 1 21 t 21 LIMITER t 21 51 600 600 f SN COMPRESSOR ad 40dB 1 hd 2 gus sap 5 gt 3 GLEN I LEVEL a F I La 1 ON q gt i LIMITER COMPRESSOR J MODE q i J A MAIN OUTPUT 3 E 36 OR 4dBu 15V LIMTER ICOMPRESSOR T N r gt 2 40dB Me PAD Ta RIGHT 5 t gt XLR M 1 2 gt MAIN OUT L gt MAIN OUT R SUMMING BALANCED BUFFER BUFFER LINE DRIVER T t 21 1 2 t 21 E b LEET 1 4 3 COND AUX MASTER LEVEL AUX OUTPUT 44dBu BALANCED LINE DRIVER RIGHT 2 1 4 3 COND 2 e gt AUX OUT L gt AUX OUT R di STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER 15V LOCATED ON BACK PANEL LOCATED ON FRONT PANEL POLARITY VS INPUT NOMINAL LEVEL IN dBul MASTER OUTPUT CARD BLOCK DIAGRAM DRAWING NO 350600 DATE 11 20 96 PAGE 04 OF 07 MAIN OUT L MAIN OUT R AUX OUT L AUX OUT R LEFT MONO 1 4 3 COND EXTERNAL MONITOR INPUT 1 4dBu RIGHT 1 4 3 COND LEFT MONO 1 4 3 COND EXTERNAL MONITOR INPUT 2 10 OR 4dBu RIGHT 1 4
5. LOCATED ON BACK PANEL LOCATED ON FRONT PANEL POLARITY VS INPUT NOMINAL LEVEL IN dBul METER L METER R PEAK LED L PEAK LED R TO SPKR POT L TO SPKR POT R TO PHONES POT L TO PHONES POT R FROM SPKR POT L FROM SPKR POT R LEFT 1 4 3 COND MONITOR OUTPUT 2dBu RIGHT 1 4 3 COND gt AUX INT SPKR LED AUX INT PHONES LED STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER MONITOR CARD BLOCK DIAGRAM DRAWING NO 30600 DATE 11 20 96 PAGE 05 or 07 1 8 FROM MONITOR CARD L SPKR LEVEL TO MONITOR CARD L FROM MONITOR CARD R gt TO MONITOR CARD R AUX INT SPKR FROM MONITOR CARD AMPLIFIER 1 8 FROM MONITOR CARD L i PHONES LEVEL i FROM MONITOR CARD R z AUX INT PHONE S FROM MONITOR CARD AMPLIFIER INTERNAL MIC t 201 FROM MICROPHONE TO SETUP CARD ON METER SUPPORT CARD VU METER Lee METER L FROM MONITOR CARD gt VU METER Ree METER R FROM MONITOR CARD gt gt CURRENT TO METER LIGHTING LEDS SOURCE QN METER SUPPORT CARD HEADPHONE OUTPUT 1 4 3 COND AC MAINS FUSE POWER HD 15V FACTORY CONFIGURABLE lt No SUPPLY FOR 100 120 220 240V 1 9 15V 50 60Hz OPERATION y POWER SUPPLY 48V 2 LOCATED ON BACK PANEL i LOCATED
6. What This User Guide Covers This User Guide is designed to assist you when installing configuring and using the Model 750 Audio Mixer A limited amount of background technical information is also provided Should you require detailed technical information please refer to the Model 750 Service Guide The Service Guide contains detailed service informa tion including schematic diagrams The Service Guide is not shipped with each Model 750 but is available from the fac tory upon request Figure 1 View of Model 750 Front Panel MODEL 750 AUDIO MIXER man oura 1 M ROUT ro awe L To e 6 9 6 CONFIGURABLE OUTPUT Figure 2 View of Model 750 Back Panel Model 750 User Guide Studio Technologies Inc Issue 3 May 1997 Page 7 Model 750 System Features Mic Line Inputs Four transformer coupled input channels are provided for connection to micro phone or line level signals The circuitry is ruggedized for reliability under tough operating conditions A full set of features is provided for each input channel includ ing selectable input sensitivity 48V phantom power low cut filter phase reverse level control and pan pot For operator assistance a bi color LED pro vides signal present and peak level indica tion Two illuminated push button switches control the routing of the input signal to the
7. so that tip is signal high or hot ring is low or cold and sleeve is shield With an unbalanced source connect the tip to high or hot and both the ring and sleeve to shield If connecting to an unbal anced source in this manner results in hum or noise connect tip to high or hot and ring to shield leave the sleeve unterminated Monitor Output The monitor output is designed for con nection to an audio power amplifier asso ciated with a pair of monitor loudspeakers In mobile applications it may prove com mon for loudspeakers with internal amplifi ers such as those from Fostex to be connected to the Model 750 s speaker output The outputs are electronically balanced line level and can drive bal anced or unbalanced loads of 600 ohms or greater The monitor output utilizes two inch 3 conductor phone jacks for interconnec tion Prepare the mating connectors plugs so that tip is signal high or hot ring is low or cold and sleeve is shield To connect to an unbalanced load con nect the tip to high or hot and both the ring and sleeve to shield Whether these outputs are wired via the patch bay will depend on the specific installation Model 750 User Guide Studio Technologies Inc Model 750 Record Talk Back External Audio Input The Model 750 contains an internal micro phone which is used by the setup section for voice recording as well as by the talk back functions In speci
8. General Audio Parameters Frequency Response 20Hz 20kHz 0 5aB stereo line in main out 1 Distortion THD N 0 04 measured at 1kHz mic in main out 3 S N Ratio 80dB referenced to 4dBu mic in main out 3 Connectors Mic Line Stereo Line 3 pin XLR type female pin 2 high Main Out 3 3 pin XLR type male pin 2 high All Other Audio 4 inch 3 conductor phone jacks AC Mains 3 blade IEC type Mic Line Inputs 4 Type balanced transformer coupled Impedance mic 1k ohms line 9k ohms Common Mode Rejection Ratio 68dB 60Hz typical Level Range Mic 70 to 10dBu Line 30 to 30dBu Range specified to give 4dBu output level master level controls set to unity gain position Microphone Power 48V phantom type Low Cut Filter 3dB at 85Hz 18dB octave slope Status LED bi color signal present peak Pan Type constant energy Pan Attenuation 60dB nominal Stereo Line Inputs 2 Type electronically balanced direct coupled compatible with balanced or unbalanced signals Impedance 24k ohms Common Mode Rejection Ratio 100dB DC 60Hz 70dB 9 20kHz 62dB 40kHz typical Nominal Level 4dBu 8 to 10dBu acceptable Status LED 2 bi color signal present peak Issue 3 May 1997 Page 38 Main Audio Bus Limiter Compressor 2 Type single knee VCA controlled non tracking Threshold 10dBu nominal 6dB above nominal output level Attack Time 2mSec nominal Release
9. While the Model 750 Audio Mixer is quite simple to operate there are nuances to its design that make a detailed discussion worthwhile While you can certainly con sider the Model 750 a small audio mixer its roots are from the much larger audio consoles that are used in broadcast and recording settings We ll start with a dis cussion of the individual sections that make up the Model 750 Then we ll review how the sections work together to become your audio master control Mic Line Inputs Four identical input channels are provided each being compatible with a microphone or line level signal A detailed description of one mic line channel follows Input Sensitivity The mic line button is used to select the sensitivity of the input circuitry In the mic out position the expected nominal input level is 55 to 35dBu In the line in position a 40dB pad is inserted into the circuit making the expected nominal input level 715 to 5dBu The input circuitry is compatible with a wide range of signal levels and is protected from overload In most cases an input signal whose nomi nal level is outside the expected range shouldn t pose a problem Phantom Power The button labeled 48V is used to acti vate phantom power for use with con denser type microphones The 48V power supply and related circuitry was carefully designed to allow virtually any microphone that requires phantom power to operate correctly
10. permanent L R voice segment needs to be re corded By placing the switch to the down position the L R voice segment cannot be changed Issue 3 May 1997 Page 21 Model 750 3 REC L ONLY R ONLY DISABLE Y ENABLE A This switch selects whether the setup section s L Only and R Only voice segments can be re corded In the down position recording cannot take place In the up position recording can take place This feature can prove useful where semi permanent L Only and R Only voice segments need to be recorded By placing the switch to the down position the L R voice segment cannot be changed 4 SINGLE TONE 400HZ Y 1KHZ A This switch selects whether the setup section s single tone feature will generate a 400Hz or a 1kHz sine wave signal In the down position 400Hz will be generated In the up position 1kHz will be generated 5 MULTI TONE SEQUENCE BASIC Y ADVANCED A This switch selects whether the setup section s multi tone feature will generate a basic or an advanced sequence of tones In the down position the basic sequence will be generated In the up position the advanced sequence will be gener ated Refer to appendices A 1 and A 2 for detailed descriptions of the tone sequences 6 AUX INT SPEAKER NO Y YES A This switch selects whether the AUX audio bus will automatically be selected as the audio source for the monitor speaker whenever an input channel or the setup section is assigned to the AUX
11. The Model 750 s master output section contains a variety of buttons and controls associated with the main and AUX audio buses Issue 3 May 1997 Page 30 MASTER SETUP DIRECT OUT AUXOUT O MIC LINE MAIN OUT LIMITER U Ld AUX MASTER LEVEL MAIN i O MASTER LEVEL Figure 12 Detail of front panel showing master output section AUX and Main Master Level Controls Two controls are used to set the overall level of the AUX audio bus The inner knob controls the level of the left channel the outer knob controls the right channel On the front panel note the small arrow graphic symbol and the letter U located at the 1 o clock rotation position This indicates the approximate setting for the level controls to give unity gain and is the position where the controls should nor mally be set Model 750 User Guide Studio Technologies Inc Model 750 Another two controls are used to set the overall level of the main audio bus They too should be set to the unity gain position except in special situations Limiter Compressors A studio quality limiter compressor circuit is associated with each channel of the main audio bus A push button switch selects the off on status when the button is in the out position the limiter compres sors are not active When the button is in the on in position high signal levels on the main audio bus will be automatically attenuated Two green LEDs
12. When the button is in Model 750 User Guide Studio Technologies Inc the off out position power is not applied to the mic line input connector When the button is in the on in position and the mic line button is in the mic out position 48Vdc is applied to the input connector When the mic line button is set for mic and a condenser microphone is con nected changing the phantom power on off status may result in loud pops being generated As such it is best not to change the position of the 48V button while its associated input is live or on air While it is a good idea to leave the 48V button in the off position except when phantom power is required no damage should occur to dynamic or ribbon micro phones when they re connected to the input with phantom voltage present Wow that s why they call it phantom power if a device doesn t require power it doesn t see it Low Cut Filter The button associated with the bent line graphic symbol is used to select the low cut filter function If you are a stickler for semantics it s actually a high pass filter function In the off out position the filter is not placed in the audio path leaving the signal essentially flat In the on in position the signal is routed through the filter circuit removing low frequency energy The filter is useful for eliminating wind noise traffic rumble and AC mains hum It was carefully desi
13. position On the setup section place the main bus assignment button to the on in position Select the main bus as the VU meter source by placing the meter source button to the monitor in position and selecting main stereo This makes the meters most accurate when they are Issue 8 May 1997 Page 20 monitoring the main bus via the moni tor section If you wish to have the meters most accurate when they are connected directly to the main bus set the meter source button to the main out position Designate main output 1 2 or in rare circumstances 3 as the desired primary output This is the output that the meters will be calibrated against If main output 3 is selected set its output level button to the line in position Confirm that the left and right channels of the designated main output are terminated with their normal load impedance Using an appropriate adapter cable connect an audio level meter directly across the left channel of the desig nated main output Ensure that the meter connection does not remove the normal load The level meter must be a precision device that s intended for audio use a general purpose volt meter is not adequate Carefully observing the audio level meter set the main bus left channel master output control so that the out put level matches the desired nominal operating level In most cases this will be 4dBu 10 Observing the Model 750 s left cha
14. 3 COND EXT 2 INPUT LEVEL 10 4 DIP 8 AUX INT SEAKER NO YES DIP 6 AUX INT PHONES NO YES DIP 7 AUX ACTIVE MIC ACTIVE MODE BUFFER MAIN S Quae aw s MONITOR es 1 gure CAL i Te AW Et z PEAK DETECT 5 SUMMING DETECT BUFFER BUFFER MAIN STEREO 1 81 W 1 8 1 21 l ran 1 STEREO D i 1 dz AW AM en 1 MONITOR gt MAIN LEF Tan MODE 4 BUFFER l 1 1 8 c8 me gt AW ave AW ve gt MAIN RIGHT a n AUX 2 21 a AM 4 BALANCED l LINE DRIVER 1 DIFFERENTIAL INPUT BUFFER K rj 1 lt m 2 LT i wm LOGIC DECODE DIFFERENTIAL INPUT BUFFER e 2 2 wm is 45V gt 4 158V IN power 2007 8V SUPPLY 15V CR ayy 15V IN OUT 8V et
15. 3 will provide its full specified performance AUX Output A stereo output is provided to give access to the Model 750 s AUX audio bus It is intended that the AUX audio output will be connected to devices within the vehicle The electronically balanced line level outputs have a nominal level of 4dBu and are capable of driving balanced or unbalanced loads of 600 ohms or greater Two inch 3 conductor phone jacks used for interconnection Prepare the mating connectors plugs so that tip is signal high or hot ring is low or cold and sleeve is shield To connect to an unbalanced load connect the tip to high or hot and both the ring and sleeve to shield Model 750 User Guide Studio Technologies Inc Even if there are no immediate plans to connect the AUX audio outputs to external devices it is recommended that they be terminated on patch points In this manner they will be accessible for those one in a million situations that seem to arise far too frequently Configurable Outputs Each of the four configurable outputs is electronically balanced has a nominal level of 4dBu and is capable of driving balanced or unbalanced loads of 600 ohms or greater The outputs are intended to be used only within the vehicle DIP switches are associated with each configurable output Details on using these switches can be found in the Con figuration section of this guide Each of the configurable outputs is
16. Model 750 User Guide Studio Technologies Inc direct output The active audio signal will only be connected to the main and or AUX buses if their respective bus assignment buttons are enabled In the following paragraphs it is assumed that these but tons have be set to their desired positions Voice Play If the button labeled VOICE is the only one selected playback of the L R L Only and R Only voice segments will occur in a continuous sequence The L R voice segment will play first connecting the recorded audio to both the left and right channels After a 1 second pause the L Only voice segment will connect to the left channel with silence on the right channel After another 1 second pause the R Only voice segment will connect to the right channel with silence on the left channel After a 2 second pause the L R voice segment will again play And so it goes If a voice segment has been electronically marked as erased it will be skipped from the playback sequence If all three seg ments have been erased then the voice play status LED will flash in a 1 second on 1 second off cadence whenever the play function is enabled Single Tone Play If the button labeled SINGLE TONE is the only one selected a continuous 400Hz or 1kHz sine wave signal will be connected to both the left and right channels Con figuration DIP switch 4 is used to select whether 400Hz or 1kHz will be generated Multi Tone Play If the
17. ON FRONT PANEL POLARITY VS INPUT NOMINAL LEVEL IN dBuJ STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER POWER SUPPLY CARD BLOCK DIAGRAM DRAWING NO 30600 DATE 11 20 96 PAGE 06 or 07 TO FROM POWER SUPPLY CARD UE PEAK L PEAK R bi METER LIGHTING ec MICROPHONE LOCATED ON FRONT PANEL STUDIO TECHNOLOGIES INC MODEL 750 AUDIO MIXER METER SUPPORT CARD BLOCK DIAGRAM DRAWING NO 30600 DATE 11 20 96 PAGE 07 o 07
18. Set the meter source button to the monitor in position 4 Set the monitor source button to main stereo 5 Adjust the main master level controls so that the meters read 0 VU The main bus is now set for precisely unity gain 6 On the setup section place the main bus assignment button to the off out position and the AUX bus assignment button to the on in position Model 750 User Guide Studio Technologies Inc 7 Ifthe AUX interrupt function becomes active due to configuration DIP switches 6 and or 7 being set to their up position the meters are now monitoring the AUX bus If the AUX interrupt function is not active set the monitor source to AUX 8 Adjust the AUX master level controls so that the meters read 0 VU The AUX bus is now set for precisely unity gain 9 The procedure has now been com pleted Return the buttons on the setup and monitor sections to the desired operating setting Signal Present Peak LEDs Bi color status LEDs are provided on the mic line and stereo line input sections Under normal operating conditions the LEDs should light only with the color green Signal peaks may cause an occa sional red flash but sustained lighting of the peak indicator means that audio per formance is being compromised Adjust the level controls so that you aren t in the red except on rare occasions Limiter Compressors While the Model 750 was designed to provides lots of s
19. The Model 750 is intended for rack mount ing requiring two standard rack spaces 3 5 inches It weights approximately 14 pounds 6 4kg and operates on either 100 120 or 200 240V 50 60Hz The unit is secured to the front mounting rails of an equipment rack using two mounting screws per side Audio Inputs and Outputs The Model 750 s audio input and output connections are made using 3 pin XLR type and inch 3 conductor phone jacks Model 750 User Guide Studio Technologies Inc Balanced Connections Input amp Output Ring Sleeve Shield Switchcraft No 297 Neutrik NP3C or equivalent Figure 3 Recommended phone plugs Don t be concerned about our use of phone jacks as part of a professional product The jacks used feature gold plated contacts for high reliability As much as we wanted to there was simply no room in only two rack spaces to use all XLR type connectors Caution For reliable audio intercon nection the phone plugs you use must comply with industry standard RS 453 Switchcraft No 297 or Neutrik NP3C are highly recommended Mic Line Inputs The Model 750 contains four input chan nels that are compatible with microphone or line level sources Each of the four Mic Line inputs use a single 3 pin female XLR type connector Prepare the mating connectors males so that pin 2 is signal high or hot pin 3 is low or cold and pin 1 is s
20. While getting some thing perfect is impossible can say that I m very pleased with how the product turned out and hope that you share my enthusiasm think that you ll find the Model 750 a plea sure to use providing the resources required for efficient easy to use day after day operation A special thanks to Tony Raven Chief Engineer at Shook Electronics USA It was Tony who suggested that Studio Technologies create an audio mixer for mobile broadcast applications He supported his idea by spending many hours with me on the telephone reviewing lists of features making comments and keeping us focused on meeting the needs of field personnel Thanks again Tony Many other broadcast professionals contributed their time expertise and good ideas to help make the Model 750 what it is Without their help the unit would definitely not be as finely tuned as it is Thanks to you all Many people at Studio Technologies contributed toward making the Model 750 a reality Fred Roeck did the mechanical design and prepared the production documentation Carrie Loving designed the graphics and provided engineering CAD support Al Lux de signed the printed circuit boards Mitch Budniak Ace Consulting Engineer designed the power supply and did several overall reality reviews Jim Cunningham with assistance from Gary Hebert at THAT Corporation designed the limiter compressor circuit Joe Urbanczyk designed the computerized test rou
21. acces sible via a 4 inch 3 conductor phone jack Prepare the mating connectors plugs so that tip is signal high or hot ring is low or cold and sleeve is shield To con nect to an unbalanced load connect the tip to high or hot and both the ring and sleeve to shield It is highly recommended that the config urable outputs be routed via the patch bay Or if there are no immediate needs for these outputs be certain to terminate them on the patch bay for future use Sometime somewhere they will get used Setup Direct Output Direct access to the setup section s voice and tone signals is provided by means of a stereo line level output As one of the unique features of the Model 750 it should definitely be utilized This output is in tended to be connected to the audio input associated with the video audio switcher s Issue 3 May 1997 Page 13 Model 750 bars and tone position For maximum flexibility it is recommended that these signals be connected by way of the patch bay In this way they can be accessed for test and calibration purposes The electronically balanced nominal 4dBu outputs are accessible via two Ya inch 3 conductor phone jacks The circuitry is capable of driving balanced or unbalanced loads of 600 ohms or greater Prepare the mating connectors plugs so that tip is signal high or hot ring is low or cold and sleeve is shield To con nect to an unbalanced load co
22. bus In the down position a signal assigned to the AUX bus will not impact the monitor speaker output In the up position any signal assigned to the AUX bus will automatically be connected to the monitor speaker output Also if the VU meter source button is set to follow the monitor section the AUX bus signals will automatically be connected to the VU meters whenever AUX interrupt is active 7 AUX INT PHONES NO Y YES A This switch selects whether the AUX audio bus will automatically be selected as the audio source for the headphone output whenever an input channel or the setup section is assigned to the AUX bus In the down position a signal assigned to the AUX bus will not impact the headphone output In the up position any signal assigned to the AUX bus will automatically be connected to the headphone Issue 3 May 1997 Page 22 output Also if the VU meter source button is set to follow the monitor section the AUX bus signals will automatically be connected to the VU meters whenever AUX interrupt is active 8 EXT 2 INPUT LEVEL 10 Y 4 This switch is used to select the nominal input level of external monitor input 2 In the down position the nominal input level is 10dBu In the up position the nominal input level is 4dBu INPUT 1 O MIC SIG LINE Figure 9 Detail of front panel showing mic line input channel typical of 4 Model 750 User Guide Studio Technologies Inc Model 750 Operation
23. display the operating status of the limiter compressors They light whenever signal attenuation is taking place Note that the limiter compressor circuits operate independently for the left and right channels they do not track together Main Outputs Three stereo output connections are pro vided on the back panel providing access to the signals on the main audio bus Main outputs 1 and 2 are configured for line MONITOR MIC PEAK METER Il MAIN SOURCE MONITOR LEFT a Rae TI 4 Qf 20 1 1 LL MAIN E LEFT WU vu E m RIGHT MONITOR SOURCE m Model 750 Audio Mixer H EXT 1 EM AUX INT Il STEREO MOI LI NO speaker PHONES STEREO MONITOR Figure 13 Detail of front panel showing monitor section Model 750 User Guide Studio Technologies Inc level A button located on the front panel selects the output level for main output 3 Setting the button to the out position se lects microphone level the in position selects line level Talk Back Two buttons allow voice signals to be connected to the setup direct output and the main and AUX output buses creating a talk back function for cueing slating and setup use The talk back audio source is the same as that used by the setup sec tion s voice recording function Depending on the setting of configuration DIP switch 1 it is either the internal microphone or an externally connected line level aud
24. for monitoring A review of the sources may prove helpful Main Stereo This selects the left and right channels of the main audio bus as the monitor source left channel is routed to the left channel of the monitor section right channel to the right chan nel This selection is appropriate when stereo program audio is present on the main bus or when independent signals present on the left and right channels of the main bus need to be simultaneously monitored e Main Left This selects the left channel of the main audio bus as the monitor source The left channel is routed to both the left and right channels of the monitor section This allows a single channel monaural program feed or the left channel of a two channel split feed to be monitored An example of a split feed is where the left channel of the main bus is handling audio for network 1 while the right channel of the main bus is handling audio for network 2 Main Right This selects the right channel of the main audio bus as the monitor source The right channel is Issue 3 May 1997 Page 32 routed to both the left and right chan nels of the monitor section This allows a single channel monaural program feed or the right channel of a two channel split feed to be monitored AUX This selects the left and right channels of the AUX audio bus as the monitor source left channel is routed to the left channel of the monitor section right ch
25. input signals to be routed and if desired combined before being sent to the main and AUX bus assignment buttons The four routing buttons provide a unique and powerful function allowing the left and right input signals to be routed in any manner desired not simply the left input connects to left output and the right input connects to right output situation that is found in most audio mixers This flexibility is provided specifically for broad cast applications where a source signal SINGLE MULTI TONE AUX Figure 11 Detail of front panel showing setup section Model 750 User Guide Studio Technologies Inc Model 750 may consist of a true stereo signal a dual channel monaural signal or one or two independent monaural signals Associated with the left channel input are two buttons labeled OUT L and OUT R When both buttons are in the off out position the left input signal can t be connected to the left or right output bus The final connection to the buses actually occurs by means of the bus assignment buttons Placing the OUT L button in the on in position allows the left input signal to be connected to the left output buses OUT R allows the left input to be con nected to the right output buses Placing both buttons to the on in position allows the left input signal to be connected to both the left and right output buses Two buttons are associated with the right channel input
26. main and auxiliary AUX audio buses For convenience the four mic line input sensitivity buttons like all the Model 750 s operator controls are located on the front panel Stereo Line Inputs Two stereo line level input channels are provided and are intended for connection with audio signals associated with video playback The channels support real world broadcast applications where left and right signals may or may not be an actual stereo pair Routing buttons allow each left and right input to be assigned to the left output bus to the right output bus to both output buses or muted A level control along with a bi color signal present peak LED supports each left and right input Two illuminated buttons control the routing of the signals to the main and AUX audio buses Main Output Signals from the mic line input channels stereo line input channels and the setup section discussed later combine to Issue 3 May 1997 Page 8 create the main audio output The main output bus is stereo but can be used to create two independent monaural audio mixes Two studio quality stereo limiter compressor circuits are provided to con trol the dynamic range of the main audio bus Far from a simple clipper each limiter compressor circuit utilizes a sophis ticated laser trimmed voltage controlled amplifier VCA integrated circuit for quiet low distortion operation For installation flexibility three sets of stereo
27. output cir Cuitry provide access to the main stereo bus two are electronically balanced line level the third is transformer balanced with its output level selectable for mic or line AUX Output The Model 750 provides a second stereo audio bus that can be configured to oper ate in either of two modes as an auxiliary AUX output or as a monitor interrupt function In the AUX output mode special applications are easily supported such as creating a mix minus feed or serving as a second stereo output for on air use Signals from the mic line input channels stereo line input channels and the setup section can be assigned to the AUX bus Access to the AUX bus is provided by means of an electronically balanced line level output In most cases however the AUX interrupt mode will be selected allowing the normal monitor source to be interrupted and the AUX signal monitored in its place Model 750 operators will find this function ex tremely useful enabling one or more of the input channels or the setup section to be monitored without interfering with signals assigned to the main output bus Two DIP switches accessible from the Model 750 User Guide Studio Technologies Inc Model 750 front panel allow the interrupt function to be configured one switch selects whether the monitor speaker output will be inter rupted by the AUX signal the other whether the headphone output will be interrupted Configurabl
28. the trim pot associated with the left channel to give the desired output level 6 Repeat steps 4 and 5 this time for the right channel External Record TB Audio Source During installation an external source of audio may have been connected to serve in lieu of the Model 750 s internal micro phone This audio source will be used for voice recording by the setup section as well as by the talk back functions The external audio source needs to have a nominal audio level of 20 to 4dBu A trim potentiometer located on the back panel directly above the record TB exter nal audio input jack adjusts the input sensitivity of the circuitry For correct operation it is crucial that this trim pot be adjusted so that the source audio level is matched with the requirements of the Model 750 The procedure is a bit convoluted but not difficult 1 Ensure that mains power is connected to the Model 750 Model 750 User Guide Studio Technologies Inc Model 750 2 Selectthe external audio source by placing front panel configuration DIP switch 1 to the down position 3 Select the main bus as the VU meter source by placing the meter source select button to the out position 4 Place the main output limiter compres sors to the off state by placing the button labeled LIMITER to the out position L MONO L Ba MONITOR INPUT al L MONO L ext MONITOR INPUT YE L MONITOR OUT TO amp Figure 7 Detail o
29. to shield If connecting to an unbalanced source in this manner results in hum or noise con nect pin 2 to high or hot and pin 3 to shield leave pin 1 unterminated For flexibility of use it is recommended that the stereo line input connections be routed through points on the patch bay Main Outputs The Model 750 contains three sets of stereo outputs associated with the main audio bus Main Outputs 1 and 2 are Issue 3 May 1997 Page 12 electronically balanced have a nominal level of 4dBu and are capable of driving balanced or unbalanced loads of 600 ohms or greater Main Output 3 is trans former balanced with its output level selectable using a front panel button for microphone or line level It is capable of driving full level into balanced or unbal anced loads of 2k ohms or greater Main Output 1 and 2 Main Output 1 and 2 are intended for connection to devices located within the vehicle It is recommended that either Main Output 1 or 2 be used as the on air source Each output utilizes two 4 inch 3 conductor phone jacks for interconnec tion Prepare the mating connectors plugs so that tip is signal high or hot ring is low or cold and sleeve is shield Whether these outputs are wired via the patch bay will depend on the specific installation Note that while the electronically balanced output circuitry is capable of driving loads of 600 ohms or greater the output level will drop slight
30. 5 minutes go ahead and install the Model 750 wire it up and then worry about the calibration You will need a highly skilled and articulate helper capable of describ ing the position of the VU meters indica tors with words such as too high down a little almost up a tad and OK you ve got it II Model 750 User Guide Studio Technologies Inc Model 750 Locating the Unit Physical access and mechanical noise are the primary factors when choosing a mounting location By its very nature as an audio mixer an operator will need easy access to all the controls as well as good sight lines to the meters In most cases the internal microphone located on the upper right side of the front panel will be used so be careful that you don t have a cooling fan blowing directly onto it As a device that contains high gain audio stages hum and noise pickup is possible through the chassis and associated ca bling Locating the unit away from devices that radiate strong AC fields is an excellent idea The left side of the Model 750 which contains the microphone preamplifiers is the area most sensitive to noise pickup Also it is possible that the Model 750 s power transformer may radiate energy into adjacent equipment It is located at the right bottom rear corner of the unit and may need to be physically isolated from sensitive equipment especially videotape recorders Mounting
31. Model 750 Model 750 Audio Mixer User Guide Issue 3 May 1997 This User Guide is applicable for serial numbers 201 and later 1997 by Studio Technologies Inc all rights reserved 5520 West Touhy Avenue Skokie Illinois 60077 U S A Telephone 847 676 9177 Fax 847 982 0747 www studio tech com 50165 597 Issue 3 Model 750 Table of Contents Foreword NF OCMC 0 7 System Faallll Bs 8 NPS PATIO A Y 10 Conmnftig ratl fi rcc CT 16 O PONS MON mee I TP 23 Technical NOTES aussi sansa aaa ka ek ik kaa ak 36 Specifications e lk kila kk map e ik n tu ci e n pe pan knn 38 Appendix A TEE 40 Appendix dp cA 41 Block Diagrams Model 750 User Guide Issue 3 May 1997 Studio Technologies Inc Page 3 Model 750 Foreword With all the pressures in life to get things done faster work more hours finish one job so you can get on to the next it s rare to get a chance to try and do something really right That s what Studio Technologies attempted to do with the Model 750 Audio Mixer The goal was simple to make a great audio mixer for ENG SNG and mobile broadcast appli cations By great we meant not just meeting specifications or price issues but to address the real needs of personnel out in the field And not only to meet their immediate needs but to provide resources that they can adopt and use in the future
32. OT USED NOT USED MIC LINE DIRECT AUX OUT R AUX OUT L MAIN OUT R MAIN OUT L donn 8 T 6 5 4 3 2 1 Figure 5 Detail of back panel showing configurable output section typical of 4 Model 750 User Guide Studio Technologies Inc Model 750 The five choices are main output left main output right AUX output left AUX output right and mic line direct e Main output left and main output right are the same signals that connect to the output circuitry associated with the main outputs e AUX output left and AUX output right are the same signals that connect to the output circuitry associated with the AUX line level output Mic line direct is a signal that is derived from its associated mic line input chan nel The signal is the same as that connected to the pan pot post input preamplifier low cut filter and phase reverse function Configurable output 1 has access to the signal from mic line input 1 configurable output 2 has access to the signal from mic line input 2 etc Using the five DIP switches associated with each configurable output simply select the source or sources desired Note the word sources more than one source can be selected As an example selecting switch 3 AUX out left and switch 4 AUX out right will produce a monaural L R version of the AUX output Selecting switch 1 main out left for configurable output 1 and switch 2 main out ri
33. Time 100mSec nominal Slope 5 1 nominal Status LED 2 limiter compressor active Outputs Main 1 Main 2 AUX Configurable and Setup Direct Type electronically balanced capacitor coupled intended to drive balanced or unbalanced loads of 600 ohms or greater Source Impedance 50 ohms nominal Nominal Level 4dBu Setup Direct Output adjustable range 2 to 10dBu Maximum Level 27dBu into 10k ohms 26dBu into 600 ohms Main Output 3 Type balanced transformer coupled intended to drive balanced or unbalanced loads of 2k ohms or greater Source Impedance mic 200 ohms line 170 ohms nominal Nominal Level mic 36dBu line 4dBu selectable Maximum Level 21dBu into 10k ohms Monitor Output Type electronically balanced capacitor coupled intended to drive balanced or unbalanced loads of 600 ohms or greater Source Impedance 50 ohms nominal Nominal Level 2dBu with monitor level control 10096 Maximum Level 21dBu into 10k ohms 20dBu into 600 ohms Headphone Output Compatibility intended for connection to head phones with impedance of 100 ohms or greater Maximum Voltage 8Vpp 100 ohm load Model 750 User Guide Studio Technologies Inc Model 750 External Monitor Inputs 2 stereo Type electronically balanced direct coupled compatible with balanced or unbalanced signals Impedance 24k ohms Common Mode Rejection Ratio 100dB DC and 60Hz 70dB 20
34. al cases it may be desirable for an external source of audio to be used in its place A 4 inch 3 con ductor phone jack allows the connection of a line level signal with a nominal level range of 20 to 4dBu Prepare the mating connector plug so that tip is signal high or hot ring is low or cold and sleeve is shield With an unbalanced source connect the tip to high or hot and both the ring and sleeve to shield If connecting to an unbalanced source in this manner results in hum or MODEL 750 AUDIO MIXER STUDIO TECHNOLOGIES 5520 W TOUHY AVE SKOKIE ILLINOIS USA 847 676 9177 MADE IN USA CAUTION TO PREVENT ELECTRICAL SHOCK DO NOT REMOVE COVER OR BACK NO USER SERVICEABLE PARTS INSIDE REFER SERVICING TO QUALIFIED SERVICE PERSONNEL AC MAINS INPUT 1 0 4A B 120v 0 2A 220 240V 50 60Hz NEE INSTRUCTION MANUAL Figure 4 Detail of back panel showing voltage configuration chart Model 750 User Guide Studio Technologies Inc noise connect tip to high or hot and ring to shield leave the sleeve unterminated It is intended that a microphone associ ated with an intercom system headset will serve as the external audio source Inter com station s often provide an amplified line level version of the mic signal It is often referred to as a hot microphone output A trim potentiometer is associated with the external audio input allowing adju
35. al generated will always appear on the setup direct output Only if the bus assignment buttons are activated will the setup signals be connected to the main and AUX audio buses This allows the buses to continue to be used for normal audio signals even while voice identification or sine wave tones are being generated What a con cept your entire audio mixer doesn t have to be tied up so you can generate a 1kHz tone for some geek at a TV station in North Dakota The author is living dangerously he has family in Minot Voice Recording Three push button switches allow you to record custom voice identification mes sages 12 seconds maximum for the L R segment 4 seconds maximum each for the L Only and R Only segments One status LED red in color is associated with the three record buttons The LED will light Issue 3 May 1997 Page 27 Model 750 steadily when recording is taking place flashing on and off during the final 2 sec onds of recording time To ensure that an existing recording will not accidentally be erased you must press and hold a record button for 2 seconds before recording will begin You must continue to press the button during the entire time you want to record releasing the button only when you want to stop recording Should you attempt to record longer than the maximum allowable time recording will automatically stop as evidenced by the record status LED turning off and the monitor speak
36. and function in the same manner The number of routing possibilities may seem almost endless but you math experts know there are actually only 16 If you spend a bit of time thinking about the routing you ll see how a variety of stereo and monaural inputs can be routed and combined to create virtually any desired stereo or monaural output Bus Assignment Signals from the left right assignment buttons are sent to the main and AUX bus assignment buttons These two buttons operate in the same fashion as described for the mic line input channels The main button assigns the line input signals to the main bus The AUX button assigns the line input signals to the AUX mix bus and enables the AUX interrupt control bus Model 750 User Guide Studio Technologies Inc Setup Functions The Model 750 s setup section will be a new animal to most operators but is really quite simple and intuitive to under stand and use The simple and intuitive part will become more obviously after you read the following section The setup section allows the recording and playback of voice identification sig nals along with the generation of sine wave audio tones Setup Direct Output and Bus Assignment A separate stereo output is provided on the back panel giving direct access to the voice and tone signals generated by the setup section Whenever one of the setup section s voice identification or tone functions is active the sign
37. annel to the right channel This selection is appropriate when stereo program audio is present on the AUX bus or when independent signals present on the left and right channels of the AUX bus need to be simultaneously monitored EXT 1 This button selects external monitor input 1 as the monitor source left input channel is routed to the left channel of the monitor section right channel to the right channel If the external source is monaural and has been connected only to the jack labeled L MONO the signal will automatically be routed to both the left and right monitor channels This allows a monau ral signal to be monitored over both the left and right channels a method that while really 2 channel monaural binau ral is comfortable and reassuring for many people EXT 2 This button selects external monitor input 2 as the monitor source It s similar to EXT 1 with the exception that its input level sensitivity is config urable using configuration DIP switch 8 Should you find the level of EXT 2 to be significantly louder or softer when compared to the other monitor sources configuration DIP switch 8 should be checked Model 750 User Guide Studio Technologies Inc Model 750 The monitor source push button switches were chosen to allow more than one source to be selected at a time The ability to simultaneously depress and lock mul tiple buttons is not a glitch but is a fea ture which can prove useful in som
38. are adjusted to give an output level of 4dBu If the setup direct output is to be used in an installation it s important that the left and right channel output levels be ad justed to precisely match the requirements of the system Even if you simply want to use the standard output level of 4dBu it s still important to confirm the factory calibration Also note that while the output circuitry is capable of driving loads of 600 ohms or greater the output level will drop slightly as the load impedance ap proaches 600 ohms A 0 5dB difference in output level can be expected as the load impedance changes from 20k ohms to 600 ohms In practice calibrating the output level is quite simple 1 Confirm that both the left and right channels of the setup direct output are terminated with their normal load impedance 2 Ensure that the Model 750 is con nected to mains power 3 Activate the setup section s single tone output by placing the single tone button to the on in position The voice and multi tone buttons should be in their off out position Issue 3 May 1997 Page 18 4 Using an appropriate adapter cable connect an audio level meter directly across the left channel setup direct output Ensure that your connection does not remove the normal load The level meter must be a precision device that s intended for audio use a general purpose voltmeter is not adequate 5 Carefully observing the level meter adjust
39. audio buses Talk Back The Model 750 includes a talk back function Two push button switches allow the selected voice source to be routed to the setup direct output and or the main and AUX outputs Issue 3 May 1997 Page 10 Mounting Connectors and Mains While the Model 750 is loaded with fea tures it only requires two spaces ina standard 19 inch rack XLR type and Y inch 3 conductor audio connectors are used for audio interconnection Mains power is factory configured for 100 120 or 220 240V 50 60Hz Installation In this section you will be installing the Model 750 Audio Mixer in an equipment rack Input and output connections will be made using the Model 750 s multitude of jacks AC mains power will then be connected During normal operation no access to the back panel of the Model 750 is required However there are five trim potentiom eters that may need to be adjusted prior to the Model 750 going into service depend ing on the requirements of the specific installation Since part of the calibration process involves observing the front panel mounted VU meters you may want to perform the calibration process on the bench prior to mounting the Model 750 in an equipment rack In addition there are a number if DIP switches that may need to be set Refer to the Configuration section of this guide for details Realistically as long as you can get the assistance of another person for about
40. button labeled MULTI TONE is the only one selected a pre configured sequence of sine wave signals will play continuously each complete sequence Issue 3 May 1997 Page 29 Model 750 being separated by a 2 second pause Each sequence provides tones for check ing frequency response as well as left right channel identifiers Configuration DIP switch 5 is used to select whether the basic or advanced multi tone sequence will be generated Refer to Appendices A 1 and A 2 for detailed descriptions of the multi tone sequences Multiple Play Functions When more than one play button is se lected a different set of rules apply If the voice button is selected along with the single tone and or multi tone button s the voice sequence of L R L ONLY and R ONLY will play once a 2 second pause will occur and then the next selected function will become active If the single tone button has been se lected along with the voice and or multi tone button s a 400Hz or 1kHz tone will be generated for 15 seconds a 2 second pause will occur and then the next func tion will become active If the multi tone button has been selected along with the voice and or single tone button s one complete basic or ad vanced multi tone sequence will be gener ated and then after a 2 second pause the next function will become active To know which function is active is simply a matter of observing the play LED indicators Master Output
41. cle identity physical location the names of technical and on air personnel mobile Issue 3 May 1997 Page 9 Model 750 telephone numbers and left and right channel identifiers can easily be sent The voice audio source is selectable with the choices being either the internal micro phone or an externally connected signal The setup section also contains a digitally controlled sine wave generator which under software control produces a O level single tone reference and multi step tone sequences The single tone output is selectable for either 400Hz or 1kHz the two industry standard frequen cies The tone sequences allow frequency response testing of a transmission chain with the choice of either a basic or an advanced sequence In the basic setting a 1kHz O level reference is generated followed by individual 10kHz 1kHz and 100Hz tones In the advanced setting a 1kHz reference is generated followed by 14 individual tones ranging from 15kHz to 50Hz At the end of each sequence a left right channel identifier is generated It consists of a short burst of 700Hz sent only to the left channel followed by two short bursts of 700Hz to the right channel While the voice and tone setup signals can be assigned to the main and AUX output buses a direct line level stereo output is also provided This allows the generation of setup and test signals without interfer ing with normal operation of the main and AUX
42. d to observe the monitor source great flexibility is possible However unless a full understanding of how the meters function in this mode is gained the flexibility can be accompanied by confusion Issue 3 May 1997 Page 33 Model 750 e With the monitor stereo mono button set to stereo and neither the speaker nor the headphone outputs being interrupted by the AUX interrupt func tion the left channel of the selected monitor source is connected to the left meter the right channel is connected to the right meter Whenever the speaker output the headphone output or both the speaker and headphone output are interrupted using the AUX interrupt function the signals on the AUX audio bus are auto matically connected to the meters left channel to the left meter right channel to the right meter e When the stereo mono button is in the mono in position the left and right monitor signals being either the normal source or AUX interrupt are added summed attenuated by 6dB and sent to both the left and right meters Speaker Output As part of the Model 750 s monitor sec tion a stereo speaker output is pro vided along with an associated level control and status LED indicator The speaker output is actually line level not speaker level It s designed to be con nected to an audio power amplifier and associated loudspeakers or amplified speakers that contain internal power amplifiers The signal source for th
43. e specialized situations An example is where a mix minus cue signal from a remotely located facility is being returned to the Model 750 by means of external monitor input 1 By selecting both EXT 1 and main stereo a composite signal is created for monitoring Monaural Function A function is provided that allows the sel ected monitor source to be combined to form a monaural signal The monaural fun ction is useful for checking a stereo audio signal s image across the left right field as well as determining its monaural com patibility When the stereo mono button is in the mono in position the left and right channels of the monitor source are com bined Summed and the level of the sum med signal is dropped by 6dB The 6dB level reduction is a standard part of the monaural function on virtually all audio consoles preventing level buildup caused by the summing of phase coherent signals The monaural function does not impact the main and AUX audio buses affecting only the monitor speaker output headphone output and the meters Note that the monaural function effects the monitor source selected by the push button switches as well as if configured and active the AUX interrupt signal Metering Two VU type meters and associated LEDs are provided for visual level monitoring The meters provide the operator with an Model 750 User Guide Studio Technologies Inc excellent sense of the average signal leve
44. e Outputs Four monaural balanced line level out puts can serve in a wide range of installa tion specific applications DIP switches located on the back panel are used to select from the five available signal sources main output left main output right AUX output left AUX output right and mic line input channel direct The DIP switches can be set to provide additional stereo outputs create monaural outputs from the main or AUX outputs or to pro vide direct outputs from the mic line input channels Monitor Section Reminiscent of much larger audio con soles the Model 750 s monitor section gives the operator an extensive set of resources Separate stereo outputs and level controls are provided for connection to a monitor amplifier and headphones In addition to monitoring the main and AUX audio buses provision has been made for monitoring two external audio sources These stereo inputs are intended to be connected to off air microwave or satel lite receivers External Monitor Input 1 is compatible with 4 signals while Exter nal Monitor Input 2 can be set using a front panel DIP switch for 10 or 4 compatibility Multiple sources can be simultaneously selected for monitoring This can prove useful by allowing for example an opera tor to simultaneously monitor a local mix Model 750 User Guide Studio Technologies Inc and an externally provided mix minus signal A mono function allows
45. e pointer accelerates and decelerates in response to audio signals The Model 750 s meter pointer moves very close to but not exactly in the manner required to be perfect For the Model 750 operator the selected meter provides a completely acceptable indication of level But as a technically oriented company we wanted to come clean about our actions Too bad so many other audio companies don t tell you that their VU meters are fakes many don t even come close to meeting the specs VU Meter Calibration From the factory the VU meters are cali brated so that a 4dBu signal level as measured on main output 1 results in a reading of O VU on the meters The meter source button is set to the monitor in position and the source is selected to be main stereo However it may be observed that the meters may no longer Model 750 User Guide Studio Technologies Inc be precisely calibrated when the meter source button is set to the main out position In this position the main audio bus is directly connected to the meters A difference of up to 0 5dB from the cali brated value could be expected This is due to tolerance variations in the compo nents of the monitor circuitry In reality only when a steady tone is present on the main audio bus will this variation become apparent During actual operation it un likely to become a factor Issue 3 May 1997 Page 37 Model 750 Specifications
46. e speaker output is either the selected monitor source or when interrupted by the AUX interrupt function the AUX audio bus If configura tion DIP switch 6 is set to the up on position any signal assigned to the AUX audio bus will automatically replace the normal monitor source The LED labeled Issue 3 May 1997 Page 34 AUX INT will light indicating that the nor mal monitor source is being interrupted by the AUX signal The speaker output is muted whenever a voice message is being recorded or one of the talk back functions is active The speaker mute limits the amount of sound that can get into the microphone and can prevent the occurrence of acoustic feed back Headphone Output A separate stereo headphone output is provided along with an associated level control and status LED indicator The phones output is designed to work well with virtually any of the contemporary medium and high impedance headphones Sony MDR 7056s were used during the design of the Model 750 their high sensi tivity made them go way loud While a bit bright in the high end for our taste their comfort and fine design make them a good choice for use with the Model 750 If configuration DIP switch 7 is set to the up on position any signal assigned to the AUX audio bus will automatically replace the normal monitor source The LED la beled AUX INT will light indicating that the normal monitor source is being interrupted by the AUX
47. el lation is not a trivial subject we recom mend that you consult one of the many fine audio textbooks that are available We ll leave it to you to use the function as required Status LED A bi color LED acts as a user confidence indication of the overall signal level in the mic line input channel s circuitry The LED will light with the color green as a signal present indicator showing that the input signal along with the gain of the input Issue 3 May 1997 Page 24 preamplifier is at least 18dB below the nominal internal operating level The LED will light with the color red as a peak signal indicator showing that the input signal along with gain of the preamplifier is within of the circuitry s maximum level Rotary Controls To address space considerations the two rotary controls associated with each mic line input channel share the same front panel space they re known as concentric pots The inner control allows adjustment of the preamplifier gain the outer acts as a pan pot Level Control The inner control is labeled LEVEL and is used to adjust the gain of the input pream plifier circuit In the fully counterclockwise position the preamplifier gain is set to its minimum and full attenuation is achieved This means that no signal continues on to the next stage of the mic line input circuitry and if configured to the configurable output on the back panel As the level control is rotated
48. er output un muting Only by releasing the record button then press ing and holding it for 2 seconds will re cording begin again Once you have com pleted recording you needn t worry about losing the information the memory circuitry will hold it for at least 10 years You should be aware that the ultimate ability to record voice segments is con trolled by means of configuration DIP switches 2 and 3 located on the lower right corner of the front panel Switch 2 enables and disables the recording of the L R segment switch 3 applies to both the L Only and R Only segments Recording will not take place if a function is disabled no matter how long you press and hold its button There may be special cases where you don t want to record and playback all three voice segments wanting only one or two of them to be active To facilitate this an erase function is provided A voice segment is erased by pressing and holding its associated record button until recording begins as evidenced by the record LED lighting then immediately releasing the button Technically the Issue 3 May 1997 Page 28 software that controls the setup section interprets any recording of less than 1 second as an erase indication During playback a voice segment that has been erased will be skipped An operational example may be useful Once upon a time a Model 750 was used to split feed two separate news net works The L Only segme
49. ey expect to be mated with plugs that do too Should a connection seem flaky sound noisy or make intermittent contact the most likely problem is a nonstandard phone plug Replace the plug if this is the case You should find that all plugs from Switch craft or Neutrik will work correctly specifi cally Switchcraft No 297 or Neutrik NP3C In our experience headphones are the most likely place to find nonstandard plugs we even found them on some world class headphones that we use in our lab Issue 3 May 1997 Page 36 Definition of Level Studio Technologies has opted to use the dBu designation as it seems to be quite rational Using dBm was fine when all audio outputs were terminated with 600 ohm loads In this way it was easy to say that OdB was 1 milliwatt dissipated in the known load i e OdBm across 600 ohms will measure 0 775V Today an output is rarely terminated with 600 ohms generally 10k ohms or higher The dBu designation is better because it refers to dB referenced to 0 775V with load impedance not a factor This takes into account the contem porary audio scene where most equip ment has a low output source impedance and a high input impedance External Monitor Input 2 This section is buried here because we are almost certain that no one in manage ment will ever read this far into the guide Sources connected to the external monitor inputs will usually have a nominal level of 4dBu so
50. f back panel showing trim pots for VU meter calibration Model 750 User Guide Studio Technologies Inc 5 Set the main bus master output level controls to the unity gain position The front panel contains a graphic arrow symbol and the letter U to serve as a guide 6 Press and hold the button labeled TALK TO MAIN AND AUX This con nects the external audio source to the main and AUX audio buses 7 With a normal voice signal coming from the external audio source adjust the trim pot so that the VU meters deflect to the 0 VU position on signal peaks You may want to enlist the help of another person to serve as a live audio source while you make the adjustment It is very important that the external audio level reflect normal operation if your operators or pro ducers love to yell and scream set the trim pot accordingly VU Meter Calibration Two trim potentiometers allow calibration of the VU meter s normal operating level The range of the trim pots allow 0 on the meters to represent an output signal level of 2 to 10dBu While providing a power ful feature these trim pots must be ad justed very carefully Be warned meter calibration effects the audio performance of the entire Model 750 From the factory the VU meters are calibrated so that 0 VU represents an output level of 4dBu on main output 1 when loaded with 100k ohms In certain cases it may be a good idea to check the meter calib
51. ght for configurable output 2 will result in another stereo output viola main output 4 It would be the author s choice to use the configurable outputs in this way Configurable output 1 set for a mono version of the main output configurable output 2 set for a mono version of AUX output and configurable outputs 3 and 4 Model 750 User Guide Studio Technologies Inc E SETUP DIRECT OUTPUT A LEVEL TRIM REC TB EXTERNAL AUDIO IN Figure 6 Detail of back panel showing level adjustment trim pots for setup direct output set for mic line direct outputs Terminating on the patch bay these four outputs could provide quite handy for those once in a blue moon situations that seem to occur about once a month The two mic line direct outputs may prove especially helpful providing two channels of mic line amplifier for general purpose or emergency use In special situations a signal of virtually any audio level could be bumped to nominal 4dBu Issue 3 May 1997 Page 17 Model 750 Setup Direct Output The setup direct output is a stereo line level output that provides direct access to the voice and tone signals Trim potenti ometers allow adjustment of the output level from approximately 2 to 10dBu The trim pots are located on the back panel directly above the setup direct output s 14 inch phone jacks At the fac tory these outputs are loaded with 100k ohms and then the trim pots
52. gned to give a steep slope 18dB octave with the 3dB point at 85Hz For most voice applications the filter can be left activated For wide band width signals such as music the filter should be used only as necessary Issue 3 May 1997 Page 23 Model 750 Changing the on off status of the low cut filter will result in little or no noise being added to the audio signal While it is better to set the filter s button to the desired position prior to being live it can cer tainly be used at any time Phase Reverse The button associated with the circle with a slash graphic symbol is used to select the phase reverse function Many people will know this as and is techni cally a polarity invert or polarity reverse function In the normal out position the mic or line input signal maintains the same polarity from input all the way through to the main and AUX audio buses In the reverse in position the signal is inverted by 180 degrees Changing from normal to reverse or vice versa will generally result in little or no audio clicks or pops being generated allowing the function to be used during on air situations This function can be useful in situations where multiple microphones are present and signal cancellation problems occur The cancellation can be caused by mis wired interconnecting cables faulty equip ment or acoustic conditions related to microphone placement As signal canc
53. hannels They are unique having the ability to support true stereo sources as well as single or two channel monaural sources that are com mon to broadcast environments The circuitry was designed for compatibility with signals that have a nominal level of 4dBu However nominal signal levels of 10 to 10dBu are perfectly acceptable Level Controls Two level controls are used to set the amount of input signal that is sent to the left right routing buttons and subse quently on to the main and AUX bus assignment buttons The inner knob controls the level of the left channel input signal the outer knob controls the right channel signal On the front panel note the small arrow graphic symbol and the letter U located at approximately the 1 o clock rotation position This indi cates the approximate setting for the level controls to give unity gain Status LEDs Two bi color LEDs serve as signal present peak indicators for the left and right signals Electrically they monitor the output of the left and right level controls The LEDs light with the color green when the signals are 18dB or greater below the Model 750 s nominal internal operating level The LEDs light with the red color when the signals are within 6dB of the maximum Input to Output Channel Routing From the level controls the signals pass to two pairs of channel assignment but tons The assignment buttons allow the Issue 3 May 1997 Page 26
54. hield It is expected that the mic line inputs will be wired to input output connector panels located on the side or rear of the vehicle It s also nice to have one or two of the inputs multed to connectors inside the vehicle allowing the quick connection of Issue 3 May 1997 Page 11 Model 750 microphone or line level signals To mini mize noise and other problems it is rec ommended that the mic line signals aren t wired by way of points on the patch bay Stereo Line Inputs The Model 750 contains two stereo line level input channels They are intended for connection to sources located within the vehicle specifically the audio output channels from videotape machines The direct coupled electronically balanced circuitry has extremely low noise high common mode rejection but no special protection from overvoltage or static Don t get us wrong the stereo line input circuitry is better than what s found on most audio mixers available today they re just not as tough as the mic line inputs The stereo line input circuitry is intended for connection to balanced line level signals with a nominal operating level of 4dBu Each stereo line input channel uses two 3 pin female XLR type connectors Pre pare the mating connectors males so that pin 2 is signal high or hot pin 3 is low or cold and pin 1 is shield With an unbalanced source connect pin 2 to high or hot and pins 1 and 3
55. ignal headroom most applications especially broadcast won t benefit from it In fact wide dynamic range in many cases will simply tax the transmission chain and lead to signal degradation Our feeling is that leaving the limiter compressor button to the on in state is your best bet If you can t think of a good reason why extended dynamic range is desired leave the limiter com pressors active Issue 3 May 1997 Page 35 Model 750 Don t misunderstand our position Ex tended dynamic range is great for music recordings We love listening to terrific classical jazz and when available pop recordings But for the applications served by the Model 750 dynamic range is not really a factor Go ahead prove us wrong and use the Model 750 to record the London Symphony Orchestra Then you should turn the limiter compressors off Technical Notes Ve Inch Plugs and EIA RS 453 An incompatibility problem lurks between some inch 2 conductor and 3 conduc tor phone plugs and the jacks found on professional audio equipment While all the plugs seem to look the same some do not comply with the industry standard called EIA RS 453 This standard defines the physical dimensions including the shape of the plug s tip It seems that some plug manufacturers don t bother to make the tip comply with the standard Why is this relevant to you Because the phone jacks used on the Model 750 do comply with the standard and th
56. in the clockwise direction the gain of the preamplifier increases Pan Pot The outer control is labeled PAN and serves as a pan pot panorama potentiom eter controlling the routing of the mic line signal to the left and right channels of the main and AUX audio buses Of course the bus assignment buttons must be in the on in position for the signal to actually be connected to the buses When the pan pot is in the fully counter clockwise position signal is sent only to the left mix buses fully clockwise only to the right A mechanical detent provides Model 750 User Guide Studio Technologies Inc Model 750 an indication of the center of the pan pot s rotation In this position signal is sent essentially equally to both the left and right buses The pan circuitry is a constant energy type ensuring that as the signal is panned across the left right stereo field the total energy sent to the buses remains constant A 3dB level increase will be observed on the left VU meter when the pan pot is set to the fully counterclockwise position You ll observe a 3dB increase on the right meter when fully clockwise Bus Assignment Located below the level and pan controls are two buttons labeled AUX and MAIN These buttons control the connection of the audio signal coming from the pan pot to the AUX and main audio buses In addition to audio signals the AUX button also controls the status of the AUX inte
57. ing of the Model 750 the guys in Studio Technologies lab did this more than once causing high SPL howls of what hap pened the recording section doesn t work anymore To keep other audio signals from interfer ing with the record audio the Model 750 s monitor speaker output is automatically muted whenever recording is taking place During initial testing it was found that this muting feature was also very useful in an unintended way providing an audible marker as to when to begin talking Using the Play Functions Three buttons are associated with the setup section s play functions Adjacent to each button is an LED indicator that lights whenever its respective function is active The uniqueness of the setup section is highlighted by the use of blue LEDs a rarity that we think adds a bit of cool ness to the Model 750 It is important to understand the operating differences between when only one of the play buttons has be set to the on in position and when more than one has been set to the on position When only one button has been selected the function associated with that button will operate continuously When more than one button has been selected the selected functions will alternate according to a pre pro grammed schedule Remember the setup section has a direct audio output This means that any time one of the play functions is active an audio signal will be present on the setup
58. io source The Model 750 s monitor speaker output is automatically muted whenever a talk back function is active Pressing and holding the talk back button labeled SETUP DIRECT OUT connects the voice audio source to the setup direct output connections The voice audio signal will be added summed with what ever signal is also present on the setup direct output a voice or tone signal present on the setup direct output will not be muted while talk back is taking place Pressing and holding the talk back button labeled MAIN amp AUX OUT connects the voice audio source to the main and AUX audio buses The voice audio signal will be added summed with whatever signals are also present on the buses Monitor Section The monitor section assists the operator in obtaining the best performance from the Model 750 It controls the signals that are presented to the VU meters and associ ated peak indicator lights speaker output Issue 3 May 1997 Page 31 Model 750 and headphone output Acting as a trusty assistant the monitor section allows visual and aural monitoring of a variety of sig nals without effecting the main and AUX audio buses Understanding and becom ing comfortable with using the monitor section is crucial to obtaining optimal Model 750 performance Source Selection Buttons The core of the monitor section are the six monitor source buttons The six buttons allow one or more of the audio sources to be selected
59. kHz 62dB 40kHz typical Nominal Level Input 1 4dBu Nominal Level Input 2 10 or 4dBu selectable Setup Section Record L R Duration 12 seconds maximum Record L Only R Only Duration 4 seconds maximum Record Audio Source internal microphone or external line level selectable Single Tone Frequency 400Hz or 1kHz selectable Basic Multi Tone Frequencies 1kHz reference followed by 10kHz 1kHz 100Hz Advanced Multi Tone Frequencies 1kHz reference followed by 14 tones 15kHz 50Hz Setup Direct Output Level 4dBu nominal adjustable range 2 to 10dBu Status LEDs 4 Talk Back Connects voice audio source to setup direct and or main and AUX outputs Record Talk Back External Audio Input Type electronically balanced capacitor coupled compatible with balanced or unbalanced signals Level Range 20 to 4dBu adjustable Metering 2 Type analog panel VU scale with signal peak LED Calibration 0 VU 4dBu nominal adjustable range 2 to 10dBu Peak LED lights at 6dB below internal bus clip level Illumination 14 LEDs 7 per meter Polarity Input to output polarity maintained except inversion on headphone output Model 750 User Guide Studio Technologies Inc AC Mains Requirement 100 120 or 220 240V 10 factory configured 50 60Hz 40 watts maximum Dimensions Overall 19 00 inches wide 48 3cm 3 49 inches high 8 9cm 9 50 inches deep 21 4cm Mou
60. l while the LEDs display peak signal condi tions A peak LED lights whenever the level of the signal being monitored reaches within 6dB of the maximum inter nal bus level In the real world audio material with large transient information may only display a moderate signal level on the VU meters While the fast response time of the peak LEDs will allow the pres ence of such transients to be displayed A push button switch located at the top of the monitor section allows the audio source for the meters to be selected When the button is in the main out posi tion the left channel of the main audio bus is sent to the left meter the right channel of the main audio bus is sent to the right meter When the button is in the monitor in position the monitor source selected for the speaker and headphone outputs is connected to the meters Reviewing the ramifications of the meter source button may prove useful we do so in the follow ing paragraphs Allowing the meters to directly monitor the main audio bus is provided for operator peace of mind It allows a continuous display of what is in most situations the on air audio bus no matter what is happening in the monitor section Note that when the meter source button is set to the main out position use of the stereo mono button will have no impact on the meters Activation of the AUX interrupt function won t affect the meters either With the meters selecte
61. ly as the load impedance approaches 600 ohms A 0 5dB difference in output level can be expected as the load impedance changes from 10k ohms to 600 ohms While balanced operation is preferred unbalanced operation is not a problem for the electronically balanced output circuitry To connect to an unbalanced load connect the tip to high or hot and both the ring and sleeve to shield For optimal unbalanced operation it is impor tant to connect both the ring and sleeve together on the plug that mates with the Model 750 Model 750 User Guide Studio Technologies Inc Model 750 Main Output 3 Main Output 3 has been optimized for connection to devices located external to the vehicle This ruggedized trans former coupled stereo output is select able using a front panel button for microphone or line level It is recom mended that Main Output 3 be wired via points on the patch bay to the vehicle s input output connector panel Two 3 pin male XLR type connectors are used for interconnection Prepare the mating con nectors females so that pin 2 is high or hot pin 3 is low or cold and pin 1 is shield Main Output 3 was specifically designed to provide a fully isolated output with good sonic performance It was NOT designed to drive full level into 600 ohm loads While a 600 ohm load can be connected without damage a 2dB level drop should be expected Used with 2k ohm or greater loads Main Output
62. means of two screws Where the Model 750 is physically located and who will be operating the unit will dictate whether the security cover remains in place or is permanently removed In a facility where many operators have access to the unit it may be best to set the con figuration DIP switches to match the needs of most operators then replace the cover In a facility where only a few operators have access such as an SNG vehicle the cover can stay off to allow quick access to the features A brief description of the function of each configuration DIP switch is contained on the front panel directly above the DIP switches A more detailed description is provided here 1 REC TB AUDIO SOURCE EXT Y INT A This switch selects which audio source will be used by the voice record and talk back sections In the down position the external audio source is selected In the up position the internal micro phone will be used Be careful with this switch In most cases an external audio source will not be connected and the internal microphone needs to be selected for use It s easy to accidentally set DIP switch 1 to the down position and have no source of record and talk back audio 2 REC L R DISABLE Y ENABLE A This switch selects whether the setup section s L R voice segment can be recorded In the down position recording cannot take place In the up position recording can take place This feature can prove useful where a semi
63. nnect the tip to high or hot and both the ring and sleeve to shield Two trim potentiometers are used to set the output level of the setup direct output Refer to the Configuration section of this guide for details External Monitor Inputs Two external audio signals can be con nected allowing them to be monitored independently of the internal audio buses It is intended that the external monitor inputs will be connected to outputs associ ated with off air microwave or satellite receivers Both inputs are stereo elec tronically balanced and interface using Y4 inch 3 conductor phone jacks External Monitor Input 1 is compatible with signals that have a nominal level of 4dBu Exter nal Monitor Input 2 is compatible with 10dBu or 4dBu signals A DIP switch located on the front panel of the Model 750 is used to set the input sensitivity Refer to the Configuration section of this guide for configuration details As an installation aid a connection made only to the jack labeled L MONO routes the signal to both the left and right input Issue 3 May 1997 Page 14 circuitry This allows a monaural signal to be monitored in a 2 channel mono format If you wish to have a mono input con nected only to the left input simply insert an unterminated plug into the associated right input jack This will break the nor mal connections that link the left and right input circuits Prepare the mating connectors plugs
64. nnel VU meter adjust the left channel meter trim pot to give 0 VU 11 Repeat steps 8 through 10 this time for the right channel Model 750 User Guide Studio Technologies Inc Model 750 CONFIGURATION SWITCHES 1 REC TB AUDIO SOURCE EXT V INT A 2 REC L R DISABLE Y ENABLE A 3 REC L ONLY R ONLY DISABLE Y ENABLE 4 SINGLE TONE 400HZ Y 1KHZ 5 MULTI TONE SEQUENCE BASIC Y ADVANCED 6 AUX INT SPEAKER NOY YES AUX INT PHONES NOY YES 8 EXT 2 INPUT LEVEL 10 Y 44 Figure 8 Detail of front panel showing configuration DIP switches Configuration DIP Switches Studio Technologies is sorry to report that the 8 configuration DIP switches had to be placed on the front panel We tried to place them on the back panel where they d be hard to reach or inside the unit where you d never find them but we just couldn t find the space just kidding The 8 configuration DIP switches are located on the front panel where you can easily get at them These switches allow impor tant operating parameters to be easily configured and then quickly changed on the fly as operating requirements dictate The factory default is to have all 8 switches set to the up position A clear plastic security cover can be used to prevent access to the configura Model 750 User Guide Studio Technologies Inc tion DIP switches One is shipped with each Model 750 being attached to the front panel by
65. nt was used to convey information relevant to network 1 and the R Only segment was used to convey information specific to network 2 A message recorded on the L R segment was not desired as it would have been sent to both networks So the L R seg ment was erased by pressing and holding the record L R button until recording began and then the button was released immediately The desired messages were recorded onto the L Only and R Only segments which were the only ones that played back The live shot went so smoothly that the field technician was promoted moved to New York City and is now earning those big bucks The audio source for the recording is either the internal microphone located between and a little above the VU meters or an externally connected source Con figuration DIP switch 1 selects which source is active Experience will teach you how to achieve the best record audio quality While conve nient the front panel microphone is prone to noise pickup Speaking closely into the front panel microphone will result in the best signal to noise ratio An external audio source such as an amplified signal coming from a noise canceling headset will lead to a more high fi recording Model 750 User Guide Studio Technologies Inc Model 750 Be Warned The easiest means of getting a very quiet recording is to have DIP switch 1 set to EXT while having no exter nal audio signal connected During initial test
66. nting 2 standard rack spaces Weight 14 0 pounds 6 4kg Specifications subject to change without notice Issue 3 May 1997 Page 39 Model 750 Appendix A 1 Basic Multi Tone Sequence Time Interval Left Channel Right Channel Seconds Frequency Hz Frequency Hz 4 1000 1000 1 Silence Silence 2 10000 10000 1 Silence Silence 2 1000 1000 1 Silence Silence 2 100 100 1 Silence Silence 500mSec 700 Silence 1 Silence Silence 500mSec Silence 700 1 Silence Silence 500mSec Silence 700 2 Silence Silence Issue 3 May 1997 Page 40 Model 750 User Guide Studio Technologies Inc Model 750 Appendix A 2 Advanced Multi Tone Sequence Time Interval Left Channel Right Channel Seconds Frequency Hz Frequency Hz 4 1000 1000 1 Silence Silence 2 15000 15000 1 Silence Silence 2 12500 12500 1 Silence Silence 2 10000 10000 1 Silence Silence 2 8000 8000 1 Silence Silence 2 6000 6000 1 Silence Silence 2 4000 4000 1 Silence Silence 2 2000 2000 1 Silence Silence 2 1000 1000 1 Silence Silence 2 700 700 1 Silence Silence 2 500 500 1 Silence Silence 2 400 400 1 Silence Silence 2 250 250 1 Silence Silence 2 100 100 1 Silence Silence 2 50 50 1 Silence Silence 500mSec 700 Silence 1 Silence Silence 500mSec Silence 700 1 Silence Silence 500mSec Silence 700 2 Silence Silence Model 750 User Guide Issue 3 May 1997 Studio Technologies Inc Page 41 BI COLOR LED 20
67. ode and should be wired accordingly Connection Wire Color Neutral N Light Blue Live L Brown Earth Ground E Green Yellow Because the Model 750 contains no power switch it will start operating as soon as AC mains power is connected Configuration As in life power leads to responsibility The Model 750 is no exception as its features flexibility and operational power leads to a number of configuration issues that must be reviewed once installation has been completed All are quite simple and with the exception of the front panel configuration DIP switches will only need to be addressed once Configurable Outputs The Model 750 contains four configurable outputs the likes of which aren t found on other audio mixers Their uniqueness may make them seem a bit confusing at first glance However they aren t too weird simply being electronically balanced output circuits whose input source is selectable rather than being fixed The hardest part of using the configurable Issue 3 May 1997 Page 16 outputs is deciding which audio source or sources should be assigned to which output By carefully reviewing the choices and how their selection may benefit an installation the power of this humble out put should become apparent These four outputs may well eliminate the need for external distribution amplifiers combining amplifiers and microphone preamplifiers OUTPUT SELECT SWITCHES SUM NOT USED N
68. r rupt control bus AUX Bus Assignment The assignment button labeled AUX con trols the routing of the left and right audio signals to the AUX audio bus In the off out position signals are not routed to the bus and the AUX interrupt control bus is not enabled In the on in position the signals are routed to the AUX audio bus and the AUX interrupt control bus is en abled A status LED orange in color and visible through a window in the button lights whenever the button is in the on position Note that enabling the AUX interrupt control bus may or may not have a noticeable effect on the Model 750 s operation It will depend upon the settings of configuration DIP switches 6 and 7 Model 750 User Guide Studio Technologies Inc Main Bus Assignment The button labeled MAIN controls the assignment of the left and right audio signals to the main audio bus In the off out position the signals are not con nected to the main bus in the on in position the signals are connected to the main audio bus A status LED green in color and visible through a window in the button lights whenever the button is in the on position INPUT 5 m LE INL PK Mou INR PK OUT R y Figure 10 Detail of front panel showing stereo line input channel typical of 2 Issue 3 May 1997 Page 25 Model 750 Stereo Line Inputs The Model 750 contains two identical stereo line input c
69. ration such as when main outputs 1 and 2 are loaded with 600 ohms or when main output 3 is going to serve as the primary output In some installations it may be desirable to have a level different from 4dBu such as Issue 3 May 1997 Page 19 Model 750 OdBu to serve as the O reference While Studio Technologies is not excited about such a prospect it can certainly be achieved There is one serious downside to changing the nominal operating level the limiter compressor threshold The limiter compressors are designed to activate at approximately 6dB above the Model 750 s internal operating level corresponding to an output level of t 10dBu The threshold is not factory calibrated and is not easily modified in the field If as an example the meters are re calibrated for a nominal output level of OdBu the limiter compressors will now activate at 10dB above this new nominal level Prior to changing the operating level a discussion with personnel at the factory may be warranted Call us for a chat While not difficult meter calibration is a bit tedious 1 Ensure that mains power is connected to the Model 750 Place the main output limiter compres sors to the off state by placing the button labeled LIMITER to the out position Activate the setup section s single tone output by placing the single tone button to the on in position The voice and multi tone buttons should be in their off out
70. signal Unlike the speaker output the phones output is never muted Warning Protect your ears The Model 750 is capable of driving head phones to extremely high sound pres sure levels Hearing experts advise against continuous extended play especially at high levels Polka music has been found to be especially dan gerous so please be careful Model 750 User Guide Studio Technologies Inc Model 750 Practical Operating Tips Now that we ve reviewed all the sections that comprise the Model 750 it s time to actually use the unit In the following paragraphs some suggestions about how to best use the Model 750 are provided Setting the Bus Operating Levels The main and AUX master level controls allow the overall gain structure of the audio mixing buses to be set Correctly setting these controls ensures that maxi mum audio quality will be achieved In most cases simply setting the controls to the unity gain position is appropriate the unity gain position is clearly marked on the front panel If you are a fanatic for accuracy you may want set the level controls precisely using the following procedure 1 On the setup section set the single tone button to the on in position This will cause a 400Hz or 1kHz steady tone to be generated 2 the setup section place the main bus assignment button to the on in position the AUX bus assignment button must be in the off out position 3
71. stment of the input sensitivity Refer to the Con figuration section of this guide for details Information is also provided on how to set the front panel DIP switch to select the external audio input Connecting AC Mains Power The Model 750 is factory configured to operate from AC mains power of either 100 120 or 220 240V 50 60Hz In most cases units shipped to North America are factory configured for 120V operation and are supplied with an internal 0 5A 5 x 20mm fast acting fuse Units config ured for 100V also utilize a 0 5A fuse Units configured for 220 240V operation are supplied with a 0 25A 5 x 20mm fast acting fuse Before connecting the Model 750 to mains power determine the actual mains voltage and confirm that the Model 750 has been configured correctly As could be ex pected an incorrect mains configuration could seriously damage the unit Should it be necessary to change the unit s operating voltage refer to the Ser vice Guide a separate document available upon request from Studio Technologies Issue 3 May 1997 Page 15 Model 750 The Model 750 uses an IEC standard connector to mate with the AC mains cord Normally the cord supplied has a North American standard plug on one end and an IEC connector on the other In non North American applications the appropri ate plug must be attached The wire colors in the mains cord will in most cases conform to the internationally recognized CEE color c
72. the moni tored audio source to be checked for phase cancellation problems and accept able sum to monaural performance The AUX interrupt mode allows monitoring of selected input channels and the setup section without interfering with normal operation of the main audio bus For operator assistance the meters can be configured to monitor the AUX bus when ever the AUX interrupt mode is active Mechanical VU type meters along with peak level LED indicators provide a user friendly indication of audio signal levels Fanatics for addressing the details Studio Technologies has even eliminated the issue of burned out meter scale illumina tion by implementing a solid state LED based lighting scheme Setup Section Unique to the Model 750 are the features provided by the setup section the high light being the ability of the operator to record and playback three voice identifica tion segments The Left Right segment allows a voice message of up to 12 sec onds in length to be recorded with play back going to the left and right output channels The Left Only and Right Only segments allow recording of up to 4 sec onds each with playback going only to their respective channels The voice segments can prove useful allowing the facilities that receive the vehicle s signal generally provided by microwave or satellite links to quickly learn more about the origin of the trans mission Information such as vehi
73. tines for the Audio Precision System One and worked on agency approvals Larry Leviton wrote the software that drives the itty bitty micro controller in the Setup section 800 bytes in C Minas Serbekian and his crew built the prototype units ensuring that the final design was manufacturable Please contact me with your questions comments and suggestions can be reached by voice at 847 676 9177 fax at 847 982 0747 or via the Internet www studio tech com Sincerely Gordon Kapes President Model 750 User Guide Issue 3 May 1997 Studio Technologies Inc Page 5 Model 750 Introduction The unique requirements of electronic news gathering ENG trucks satellite news gathering SNG trucks and special ized remote broadcast applications demand more than just a general purpose audio mixer That s why Studio Technolo gies created the Model 750 a special piece of equipment for a special applica tion Only by taking the time to speak with industry professionals designers of ENG and SNG vehicles along with numerous field technical personnel were the neces Sary specifications established Using that information as a road map to guide the process additional features operating ergonomics and overall look and feel INPUT 1 INPUT 2 INPUT 3 INPUT 4 INPUT 5 INPUT 6 ame se PI e issues were addressed The result is a high performance easy to use audio mixer expressly designed to go on the road
74. why the 10 4 DIP switch for input 2 Frankly we thought that field engineers may sometimes want to con nect a piece of 10 consumer audio gear for their own personal monitoring While operating a remote vehicle can be challenging and fast paced it can often be filled with hours of waiting The ability to connect a compact disk player or cassette Walkman may make the time pass a little more pleasantly You might recognize that we selected 10dBu even though the 10 designation usually implies 10dBV We feel that 10dBu is a better sensitivity when con necting to 10 equipment As 10dBV 7 78dBu the extra 2 22dB of sensitivity is helpful Model 750 User Guide Studio Technologies Inc Model 750 Faux VU Meters In the spirit of George Washington and to make our mother proud of us we have to tell the truth and admit that while the meters selected for the Model 750 are of very good quality they don t meet the specifications of a true VU meter So why was a less than perfect meter se lected for the Model 750 The answer is easy and not surprising While the Model 750 s existing meter is already quite ex pensive being built in England by a top notch meter manufacturer the cost for a true VU meter is about five times as much The technical difference between the meter used on the Model 750 and a true VU meter lies in the ballistic characteris tics i e how th

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