Fostex 750 user manual

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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

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Model 750 Table of Contents Foreword Introduction .................................................................. 7 System Features .......................................................... 8 Installation .................................................................... 10 Configuration ............................................................... 16 Operation ..................................................................... 23 Technical Notes ....................................

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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 ou

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Model 750 Model 750 issues were addressed. The result is a Introduction high-performance, easy-to-use audio mixer expressly designed to go “on-the- The unique requirements of electronic road.” news-gathering (ENG) trucks, satellite news-gathering (SNG) trucks, and special- What This User Guide Covers ized remote broadcast applications demand more than just a general-purpose This User Guide is designed to assist you audio mixer. That’s why Studio Technolo- when installing, configuring, and usin

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Model 750 create the main audio output. The main System Features output bus is stereo, but can be used to create two independent monaural audio Mic/Line Inputs mixes. Two studio-quality, stereo limiter/ Four transformer-coupled input channels compressor circuits are provided to con- are provided for connection to micro- trol the dynamic range of the main audio phone or line-level signals. The circuitry is bus. Far from a simple “clipper,” each “ruggedized” for reliability under tough limiter/co

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Model 750 front panel, allow the interrupt function to and an externally-provided mix-minus be configured; one switch selects whether signal. A mono function allows the moni- the monitor speaker output will be inter- tored audio source to be checked for rupted by the AUX signal, the other phase cancellation problems and accept- whether the headphone output will be able “sum-to-monaural” performance. interrupted. The AUX interrupt mode allows monitoring of selected input channels and the setup C

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Model 750 telephone numbers, and left and right Mounting, Connectors, and Mains channel identifiers can easily be sent. While the Model 750 is loaded with fea- The voice audio source is selectable, with tures, it only requires two spaces in a the choices being either the internal micro- standard 19-inch rack. XLR-type and phone or an externally-connected signal. ¼-inch 3-conductor audio connectors are used for audio interconnection. Mains The setup section also contains a digitally- power is fa

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Model 750 Locating the Unit Balanced Connections (Input & Output) Physical access and mechanical noise are the primary factors when choosing a Ring (–) mounting location. By its very nature as an audio mixer, an operator will need easy Tip ( + ) access to all the controls, as well as good sight lines to the meters. In most cases the internal microphone, located on the upper Sleeve (Shield) right side of the front panel, will be used, so be careful that you don’t have a cooling (Switchcraft No.

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Model 750 microphone or line-level signals. To mini- electronically balanced, have a nominal mize noise and other problems, it is rec- level of +4dBu, and are capable of driving ommended that the mic/line signals aren’t balanced or unbalanced loads of 600 wired by way of points on the patch bay. ohms or greater. Main Output 3 is trans- former balanced, with its output level Stereo Line Inputs selectable, using a front-panel button, for microphone or line level. It is capable of The Model 750 co

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Model 750 Main Output 3 Even if there are no immediate plans to connect the AUX audio outputs to Main Output 3 has been optimized for external devices, it is recommended that connection to devices located external they be terminated on patch points. In this to the vehicle. This “ruggedized,” trans- manner they will be accessible for those former-coupled stereo output is select- “one-in-a-million” situations that seem to able, using a front-panel button, for arise far too frequently! microphone

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Model 750 “bars and tone” position. For maximum circuitry. This allows a monaural signal to flexibility, it is recommended that these be monitored in a 2-channel mono format. signals be connected by way of the patch If you wish to have a mono input con- bay. In this way they can be accessed for nected only to the left input, simply insert test and calibration purposes. an unterminated plug into the associated right input jack. This will break the “nor- The electronically-balanced, nominal mal”

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Model 750 noise, connect tip to high (+ or hot) Record/Talk Back External and ring to shield; leave the sleeve Audio Input unterminated. The Model 750 contains an internal micro- It is intended that a microphone associ- phone which is used by the setup section ated with an intercom system headset will for voice recording, as well as by the talk serve as the external audio source. Inter- back functions. In special cases it may be com station’s often provide an amplified, desirable for an externa

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Model 750 The Model 750 uses an IEC standard outputs is deciding which audio source, or connector to mate with the AC mains cord. sources, should be assigned to which Normally the cord supplied has a North- output! By carefully reviewing the choices, American standard plug on one end and and how their selection may benefit an an IEC connector on the other. In non- installation, the power of this humble out- North American applications the appropri- put should become apparent. These four ate plu

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Model 750 The five choices are main output left, main output right, AUX output left, AUX output right, and mic/line direct: • Main output left and main output right are the same signals that connect to the output circuitry associated with the main outputs. • 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

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Model 750 4. Using an appropriate adapter cable, Setup Direct Output connect an audio level meter directly The setup direct output is a stereo line- across the left channel setup direct level output that provides direct access output. Ensure that your connection to the voice and tone signals. Trim potenti- does not remove the normal load! The ometers allow adjustment of the output level meter must be a precision device level from approximately –2 to +10dBu. that’s intended for audio use—a The t

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Model 750 2. Select the external audio source by 5. Set the main bus master output level placing front panel configuration DIP controls to the unity gain position. The switch 1 to the down position. front panel contains a graphic arrow symbol and the letter “U” to serve as 3. Select the main bus as the VU meter a guide. source by placing the meter source select button to the out position. 6. Press and hold the button labeled TALK TO MAIN AND AUX. This con- 4. Place the main output limiter/compr

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Model 750 0dBu, to serve as the “0” reference. While monitoring the main bus via the moni- Studio Technologies is not excited about tor section. If you wish to have the such a prospect, it can certainly be meters most accurate when they are achieved. There is one serious downside connected directly to the main bus, set to changing the nominal operating level; the meter source button to the main the limiter/compressor threshold. The (out) position. limiter/compressors are designed to 6. Designat

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Model 750 tion DIP switches. One is shipped with each Model 750, being attached to the front panel by 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 opera

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Model 750 3. REC L ONLY/R ONLY: DISABLE ▼▼ / ENABLE ▲▲ output. Also, if the VU meter source button is set ▼▼▼ ▲▲▲ to follow the monitor section, the AUX bus signals This switch selects whether the setup section’s will automatically be connected to the VU meters L Only and R Only voice segments can be re- whenever AUX interrupt is active. corded. In the down position recording cannot take place. In the up position recording can take 8. EXT 2 INPUT LEVEL: –10 ▼▼ / +4 ▲▲ ▼▼▼ ▲▲▲ place. This switch

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Model 750 the off (out) position, power is not applied Operation to the mic/line input connector. When the button is in the on (in) position, and the While the Model 750 Audio Mixer is quite mic/line button is in the mic (out) position, simple to operate, there are nuances to its +48Vdc is applied to the input connector. design that make a detailed discussion worthwhile. While you can certainly con- When the mic/line button is set for mic, sider the Model 750 a “small” audio mixer, and a conden