Model 742 Model 742 Audio Mixer User Guide Issue 2, May 2005 This User Guide is applicable for serial numbers: M742-00160 and later* * For units with serial numbers 00160-00169 refer to the Technical Notes section of this user guide © 2005 by Studio Technologies, Inc., all rights reserved www.studio-tech.
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Model 742 Table of Contents Introduction ................................................................... 5 System Features ........................................................... 6 Configuration Review .................................................... 8 Installation ..................................................................... 10 Post-Installation Calibration .......................................... 15 Operation ......................................................................
Model 742 This page intentionally left blank. Issue 2, May 2005 Page 4 Model 742 User Guide Studio Technologies, Inc.
Model 742 Model 742 Introduction What This User Guide Covers This User Guide is designed to assist you when installing, configuring, and using the Model 742 Audio Mixer. Additional background and technical information is also provided, as well as a product block diagram included at the end of this guide. System Overview The Model 742 Audio Mixer is expressly designed for use in electronic-newsgathering (ENG) vehicles, small production trucks, and other specialized mobile broadcast applications.
Model 742 there’s flexibility on the inside, the operator is presented with an easy-to-use set of front-panel controls and indicators—the operator never has to access the back panel to operate the unit. In this way the goal of delivering successful on-air and production audio, day-after-day, can best be achieved. The Model 742’s audio quality is “pro” throughout. The components were carefully selected to deliver low-noise, low-distortion performance.
Model 742 associated with each main output bus. They provide line-level signals capable of driving balanced or unbalanced loads of 600 ohms or greater. Separate studioquality audio compressor circuits are provided to control the dynamic range of each main output bus. An LED indicator is associated with each compressor, lighting whenever the circuit is actively controlling signal level.
Model 742 When configured for “pre +4” operation, the monitor outputs are again “pre” the level controls, but this time with a nominal level of +4 dBu. This can be used for various applications, including providing an additional set of main bus outputs. In certain cases this may eliminate the need for an external distribution amplifier to be included as part of the installed system. Metering As previously discussed, dual-color signal present/peak LEDs are associated with each of the eight input channels.
Model 742 Phantom Power In most broadcast news applications, phantom-powered condenser microphones are not utilized. However, exceptions do arise and the Model 742 does allow 12-volt phantom power to be supplied to the four mic/line input channels. One configuration jumper is used to select the phantom power on/off status for all four channels; independent control is not provided. From the factory phantom power is selected to be off.
Model 742 Reference Tone Frequency System Components From the factory the frequency of the reference tone is configured to be 400 Hz. This is a nice alternative to the more typical 1 kHz, a frequency which can soon become very annoying to a listener’s ears. In most cases 400 Hz will be perfectly acceptable, and actually preferred.
Model 742 Mounting The Model 742 is intended for mounting in a standard 19-inch equipment rack, requiring 1.75 vertical inches (one standard rack space). It weighs 8.7 pounds (4.0 kg) and operates on mains power of 100, 120, or 220/240 volts, 50/60 Hz. The maximum current draw is less than 0.2 amperes. Four mounting screws, two per side, are used to secure the unit into the equipment rack.
Model 742 Detail of back panel showing line input connectors signals can also be connected. In this case, pin 2 is connected to signal high (+ or hot), and pins 1 and 3 are connected to shield. If this results in hum or other noise being present, try connecting pin 2 to signal high and shield to pin 3; leave pin 1 unconnected (“floating”). To provide maximum flexibility, it is recommended that the signals connected to the line inputs be wired by way of points on an audio patch bay.
Model 742 The main outputs utilize 3-pin male XLRtype connectors for interconnection. Prepare the mating connectors (females) so that pin 2 is signal high (+ or hot), pin 3 is low (– or cold), and pin 1 is shield. Whether these outputs are wired via a patch bay will depend on the specific installation. But at least having “mults” of the main outputs on patch points is probably a good idea. While balanced operation is generally preferred, unbalanced operation is not a problem for the output circuitry.
Model 742 In this way it can be easily accessed for other test and calibration purposes. The reference tone direct output is electronically balanced, has a nominal +4 dBu level, and is accessible via a ¼-inch 3-conductor jack which is located on the back panel. The output circuitry is capable of driving a balanced or unbalanced load of 600 ohms or greater. Prepare the mating plug so that tip is signal high (+ or hot), ring is low (– or cold), and sleeve is shield.
Model 742 Detail of back panel showing AC mains power connector 120 volt operation and are supplied with an internal 0.2 A, 5 x 20 mm time-lag fuse. Units shipped to Japan are factory configured for 100 volt operation and use the same 0.2 A, 5 x 20 mm time-lag fuse. Units configured for 220/240 volt operation are supplied with a 0.1 A, 5 x 20 mm time-lag fuse.
Model 742 4. While carefully observing the level meter, adjust the trim pot to give the desired output level. Labeling the Unit for Clarity Detail of back panel showing reference tone direct output connector and associated level trim pot Depending on the Model 742’s internal configuration the tone frequency will be either 400 Hz or 1 kHz. A trim potentiometer allows adjustment of the output level over a range of approximately +3 to +7 dBu.
Model 742 For a great look it’s recommended that Brother® P-Touch ¼-inch (6 mm) labels be created. Selecting tape material that prints white text on a black background works out perfectly for the Model 742. The Brother label cassette number TX-3151, white on black, is appropriate for use with some of their printers. Operation While the Model 742 Audio Mixer is quite simple to operate, there are nuances in its design that make a detailed discussion worthwhile.
Model 742 will light red as a peak signal indicator, showing that the input signal, along with the gain of the preamplifier, is within 6 dB of the circuitry’s maximum level. Level Control The rotary control is used to adjust the gain of the input section’s preamplifier circuitry. It also controls the amount of signal that can be sent to the output bus (or buses). In the fully counterclockwise position the preamplifier gain is set to its minimum, and full attenuation to the bus (or buses) is achieved.
Model 742 Master Section/Main Output Buses The Model 742’s master section supports output buses 1 and 2 with several controls and switches, compressor circuitry, and level and status indications. The following sections provide detailed descriptions of each of them. Master Level Controls Two rotary controls are used to set the overall level of output buses 1 and 2. The controls are “concentric” type, with the inner knob controlling bus 1 and the outer knob controlling bus 2.
Model 742 world where maximum audio fidelity is the goal, the LEDs should rarely, if ever, light. Level Meters Two 10-segment LED meters display the level present on main outputs 1 and 2. Each meter has seven green LEDs which light in the presence of signals in the normal operating range. Two yellow LEDs light with signals slightly higher in level than normal. One red LED lights whenever the signal level is in the “headroom” area.
Model 742 • If the compressors have been configured not to function (disabled), the meters will get their biggest workout. Depending on the setting of the input and master output controls, all ten segments of each meter may often come into play. Reference Tone A sine-wave tone can be connected to the two output buses, serving as a reference signal for local and remote use. A pushbutton switch selects its status; when the switch is in its on (in) position tone is connected to both output bus 1 and 2.
Model 742 Level Controls The rotary controls are always used to adjust the output level of the headphone output channels. Like the master output controls, they are concentric, the inner knob controlling channel 1 and the outer knob channel 2. Depending on how the monitor output mode is configured, the rotary controls may also adjust the levels of the connected loudspeakers.
Model 742 Setting the Output Bus Operating Levels The two output bus master level controls allow the overall gain structure of the main audio buses to be set. Correctly setting these controls ensures that the best audio quality will be achieved. In most cases simply setting both controls to the unity gain position is appropriate; the unity gain position is clearly marked with a “U” on the front panel.
Model 742 Compressor Configurations The compressor circuits that control the dynamic range of the main output buses can be configured to operate from one of three modes. Two configuration jumpers, one for each compressor circuit, are used to select which mode is active. From the factory the jumpers are placed across the pins labeled +10 dBu. This sets the thresholds to be 6 dB above the main outputs’ +4 dBu nominal output level.
Model 742 Be careful not to adjust the trim pot that is labeled TONE LEVEL. This adjusts the output level of the oscillator to give precisely –2 dBu to the main audio buses when the front-panel tone button is enabled. Should this pot have to be readjusted the procedure is quite simple: measure across the COM and TONE test points and adjust the trim pot to give –2 dBu. The measurement equipment must have a high input impedance (>2 k ohms) so as not to load the oscillator’s output.
Model 742 Mic/Line Switching Serial Numbers 00160-00169 As previously discussed, the four mic/line input circuits can be selected for compatibility with microphone or line-level signals. For compatibility with line-level signals a 43 dB balanced attenuator (“pad”) is connected between an input connector and its associated microphone preamplifier circuit. Front-panel pushbutton switches are used to select whether the pads are bypassed (mic input setting) or active (line input setting).
Model 742 Specifications General Audio Parameters: Compressors: 2 Function: controls dynamic range of output buses 1 and 2 Frequency Response: 20 Hz to 20 kHz, ±0.5 dB, mic/line in to main outs Type: single-knee, VCA-controlled Distortion (THD+N): 0.
Model 742 Reference Tone: Frequency and Wave Form: 400 Hz nominal, sine wave (technician can revise to 1 kHz) Direct Output Level: +4 dBu, nominal, adjustable over –1/+3 dB range Direct Output Type: electronically balanced, capacitor-coupled, intended to drive balanced or unbalanced loads of 600 ohms or greater Direct Output Source Impedance: 100 ohms, nominal Meters: 2 Function: displays level of output buses 1 and 2 Type: 10-segment LED, modified VU ballistics Connectors: Mic/Line and Line Inputs: 3-pin f
