Model 740 Model 740 Audio Mixer User Guide Issue 3, May 2004 This User Guide is applicable for serial numbers: M740-00151 and later © 2004 by Studio Technologies, Inc., all rights reserved www.studio-tech.
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Model 740 Table of Contents Introduction ................................................................... 5 System Features ........................................................... 6 Configuration Review .................................................... 8 Installation ..................................................................... 9 Post-Installation Calibration .......................................... 14 Operation ......................................................................
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Model 740 Model 740 Introduction What This User Guide Covers This User Guide is designed to assist you when installing, configuring, and using the Model 740 Audio Mixer. Additional background technical information is also provided. A product block diagram is included at the end of this guide. System Overview The Model 740 Audio Mixer is expressly designed for use in compact electronicnews-gathering (ENG) vehicles. Many other audio production applications can also be supported.
Model 740 Reliability over the long haul was a Model 740 design criteria. To that end the unit’s enclosure is made of steel, combining strength with effective RF rejection. On the inside, all components are mounted on an FR4 (fiberglass-based) circuit board assembly. System Features Mic/Line Inputs Six input channels are provided for connection to microphone or line-level signals. The electronically balanced circuitry is “ruggedized” for reliability under tough operating conditions.
Model 740 to be monitored. This allows monitoring of the main audio bus, along with two external monaural audio sources. These external monitor inputs are intended to be connected to devices such as off-air, microwave, or satellite receivers. Alternately, other mobile broadcast support equipment, such as a PC-based editing system, can be connected. Unique to the Model 740 is the ability to configure the monitor output to meet the needs of the “real world.
Model 740 is connected directly to the Model 740 by way of a standard 3-pin detachable IEC cord set; no external power supply is used. AC mains power is factory configured for 100, 120, or 220/240 V, 50/60 Hz. Configuration Review In this section you will be reviewing the configuration of the Model 740. Configuration changes can be made if required. Any changes should be made prior to installing the unit.
Model 740 to adjust its volume. This prevents the confusing situation of having two level controls—the Model 740’s level control and the amplified speaker’s level control—both impacting the speaker level. In this case the Model 740’s front-panel control will only impact the headphone output level. Meter Source The meter source can be configured to operate from one of two modes: • From the factory the meter is selected to always monitor the level of the main output bus.
Model 740 equipment. It is located at the far right side of the unit, and may need to be physically isolated from sensitive equipment such videotape recorders. 740’s 3-pin IEC 320 C14-compatible inlet connector. During normal operation, access to the Model 740’s back panel is not required. However, there is one trim potentiometer that may need to be adjusted prior to the Model 740 going into service. This trim pot sets the level of the reference tone direct output.
Model 740 Main Output—General Information The Model 740 contains one output that is associated with the main audio bus. It is electronically balanced, capacitor coupled, and has a nominal level of +4 dBu. The output circuitry is capable of driving balanced or unbalanced loads of 600 ohms or greater. Note, however, that as the load impedance approaches 600 ohms the output level will drop slightly. A 0.5 dB difference in output level can be expected as the load impedance changes from 10 k ohms to 600 ohms.
Model 740 monaural, electronically balanced, and have a nominal level of +4 dBu. Audio sources are connected to the external monitor input’s 3-pin female XLR-type connectors. Prepare 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 both pins 1 and 3 to shield.
Model 740 connect pin 2 to high (+ or hot) and both pins 1 and 3 to shield. A trim potentiometer, accessible from the back panel, is used to set the precise output level of the reference tone direct output. After an installation has been completed it may be desirable to set the trim pot to provide the required level. For details please refer to the Post-Installation Calibration section of this user guide.
Model 740 Before connecting the Model 740 to AC mains power, determine the actual mains voltage and confirm that the Model 740 has been configured appropriately. As could be expected, an incompatible mains voltage configuration could seriously damage the unit. Should it be necessary to change the unit’s operating voltage contact Studio Technologies’ technical support personnel for details. The Model 740 uses a 3-pin IEC 320 C14-compatible inlet connector to mate with a detachable mains cord set.
Model 740 3. Using an appropriate adapter cable, connect a high-input-impedance audio level meter directly across the reference tone direct output. Ensure that this 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 voltmeter is not adequate! For a great look it is recommended that Brother® P-Touch ¼-inch (6 mm) labels be created.
Model 740 In the mic (out) position, the expected nominal input level range is –55 to –35 dBu. In the line (in) position, a 43 dB pad is inserted into the circuit, making the expected nominal input level range –12 to +8 dBu. Status LED A bicolor LED acts as a user-confidence indication of the overall signal level in the mic/line input channel’s circuitry.
Model 740 dynamic range of the main bus. The operating threshold of the compressor and associated LED depends on how the Model 740 has been configured: • From the factory the compressor threshold is set to be 6 dB over the Model 740’s nominal operating level. This correlates to a level on the main output connector of +10 dBu. with signals slightly higher than normal. The red LED will light whenever the signal level is in the “headroom” area.
Model 740 (Remember that 0 VU typically indicates a device’s reference operating level— frequently +4 dBm.) The seven green LEDs display a dynamic range of 28 dB, with thresholds of –24 dBu, –18 dBu, –12 dBu, –8 dBu, –4 dBu, 0 dBu, and +4 dBu. This is the range that typical signals should display if correct settings have been made to the input sensitivity switches, input level controls, and master level control.
Model 740 A rotary control sets the output level of the headphone outputs and, depending on the Model 740’s configuration, may also control the level of the monitor output loudspeaker. Understanding and becoming comfortable with using the monitor section is important in obtaining optimal Model 740 performance. Source Selection Switch A 3-position toggle switch is used to select which one of the three audio sources is to be monitored.
Model 740 outputs are compatible with stereo headphones but really provide a 2-channel monaural audio signal. Technically, one output driver circuit connects, by way of two series resistors, to both the tip (“left”) and the ring (“right”) jack connections. In this way the Model 740’s monaural main output (and mono external monitor inputs) will correctly drive the left and right channels on a pair of stereo headphones.
Model 740 be adjusted to reduce the amount of signal being sent to the main audio bus. Also, the position of the master level control should be checked to ensure that it is set correctly. In most cases it should be set to the reference position, marked “U” for unity gain. Technical Notes Configuration Changes Warning: A competent technician is required to perform any configuration review or changes. The cover of the Model 740 must be removed to access the configuration jumpers.
Model 740 Reference Tone Frequency Configuration Two shorting jumpers are used to select the frequency range of the reference tone oscillator. A trim potentiometer is then used to set the frequency to the exact desired value. From the factory the frequency of the reference tone is set to be 400 Hz. This is accomplished by first setting the jumpers to the two locations that are labeled 400HZ. Then the trim pot is adjusted to give a 400 Hz signal when measured between the common and tone test points.
Model 740 microphone selection (or adding a windscreen) will resolve the issue. Alternately, personnel “down stream” in an editing suite or at a live audio console can apply a high-pass filter. • Allowing operator adjustment of the compressor function was certainly a possibility. But frankly, it would guarantee that often audio performance would be compromised. The Model 740’s compressor circuit was optimized for the unit’s intended application.
Model 740 Specifications General Audio Parameters: External Monitor Inputs: 2, monaural Frequency Response: 20 Hz-20 kHz, ±0.5 dB, mic/line in to main out Type: electronically balanced, direct-coupled, compatible with balanced or unbalanced signals Distortion (THD+N): 0.
Model 740 Metering: Type: 10-segment LED, modified VU ballistics Source: configurable, choices are 1) display level of main output bus (factory default), 2) source selected for monitor output Connectors: Mic/Line and External Monitor Inputs: 3-pin XLR-type, female Main, Reference Tone Direct and Monitor Outputs: 3-pin XLR-type, male Headphones: ¼-inch 3-conductor phone jacks AC Mains: 3-blade, IEC 320 C14-compatible (mates with IEC 320 C13) AC Mains Requirement: 100, 120, or 220/240 V, ±10%, factory configu
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