Assessments - 2, GPA: 4.5
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It is difficult, however, determine the proper fuse va! with the correct time lag a:; overload characteristics to mat the limitations of a speaker sy tem. The values shown in Table I should serve only as a guide. 4 ALTEC LANSING* CORPORATION • a Mark IV Company Operating and Service Instructions for the Altec Lansing 9444B Power Amplifier INPUT POWER AMPLIFIER STEP-UP TRANSFORMES 70. 100. 140, OR 210 VOLTS LONG CABLE RUN (SHALL GAUGE WIRE) LOUDSPEAKER STEP-DOWN TRANSFORMER Figure 5 High-voltage Distribution System use, determine the power rating and load value. Then, select a standard value fuse of the next smaller value to the one listed Ln the table. Table II Calculated Output Fuse Values Power 4 ft 8ft 16 ft (wutis) Load Load Lead 100 3-70 2.62 1.85 150 4.54 3.21 2.27 200 5.24 3.70 2.62 300 6.42 4.54 3.21 -100 7.41 5.24 3.70 600 9.07 6.42 4.54 The values are calculated for fast-blow fuses which carry 135% of their current rating for an hour but will blow within 1 second at 200%. Other fuse values may be calculated for different power levels from the following equation: Fuse value = (Pout x ZL)‘~ amps ZL x 1.35 where Pout is the output power rating of the amplifier; and ZL is the load impedance. Use 32 volt fuses if possible; they typically have the lowest internal resistance which will help minimize deterioration of the damping factor at the load. Refer to the example in Figure 4. 3.7 Compression Driver Protection Capacitors Compression drivers, used for mid to high frequency sound reproduction, are much more susceptible to damage from low frequencies than large cone loudspeakers. Even though an electronic crossover may be employed, problems may arise in the cables between the crossover and the power amplifier, or from rnisad-justment of the crossover. Either of these situations could apply low frequency signals or hum to the driver and cause damage. To prevent a potential mishap, Altec Lansing recommends a capacitor between the am r and the compression drive: suppress low frequencies ssible DC. Refer to the exa- a Figure 4. In choosing a value, ust be careful not to interIV Ji the crossover frequency. ;sneral rule, select a capa whose break frequency, with ¿to the load, is 3 dB down at imate- ly Vs of the high per sr frequency. Mylar capacitors wit ?ast a 100 volt ac ratingar amended. Table III show recommended capacitor for use with 8 and 16 ohm at popular crossover freqi. Table III Compr; ion Driver Protection Capacitor; Crossover 811 16 ft Frequency Drivur Driver 500 Hz 80 jiF 40 nF 800 Hz 50 nr 25 nF 1000 Hz 40 nF 20 p.F 1250 Hz 33 jiF 16 uF 2000 Hz 20 |iF 10 iiF 3150 Hz 12 (lF 6 tiF 6300 Hz 6 tiF 3 (tF 4 OCTAL ESSORY SOCKETS Two octal s; 5 permit a variety of plug-in a. :es to be used with the ampl i r -lormally, one “U” jumper rted between octal socke: 8 and 1, and another betw< ¿s 7 and 6. These jumpers n . cmain in place for the an; ; o operate when not using accessor}1 modules. To use wi ,h accessory module, remove save) the jumpers and insi . module making sure the its center post aligns with tii >ve in the female socket. For a lion, refer to the instruction ided with ALTEC LANSING* CORPORATION ® a Mark IV Company 5 Operating and Service Instructions for the Altec Lansing 9444B Power Amplifier the module. Schematically, the module will be inserted between the input connector and the balanced input stage. Electronic modules are powered from a bipolar 15 volt supply in the amplifier. The supply is capable of supplying up to 25 ma DC of current. Currents in excess of 25 ma DC may prevent the amplifier from disengaging from its built-in protection mechanisms. 5 PROTECTION SYSTEMS 5.1 Load Protection Circuitry Each channei independently protects its load from startup/shutdown transients, DC, and large subsonic signals. 5.2 Amplifier Protection Circuitry A unique current-limiting circuit was designed specifically for the amplifier. It features a variable current limit which is a function of the output signal voltage. As a result, the amplifier can deliver the rated currents into rated loads but substantially limits the current into low impedance or shorted loads (shorted output terminals). Once the short is removed, however, the amplifier will resume normal operation. A dual speed fan is also incorporated to provide efficient cooling under the most demanding conditions. When the heatsink temperature at the fin tips reaches approximately 88 °C (190 °F), the fan automatically switches to high speed operation. As the temperature cools to approximately 78 °C (172 °F), low speed operation is once again resumed. The heatsink is also thermally equalized to prevent the output devices nearest the fan from operating at a cooler temperature than the devices at the opposite end. This minimizes the thermal gradient across the heatsink and forces the devices to operate at more nearly the same temperature. This equalizes the lifetimes and reliability...
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