User manual MACKIE M-1200

[. . . ] TM FULL SYMMETRY DUAL DIFFERENTIAL HIGH CURRENT DESIGN PROFESSIONAL POWER AMPLIFIER CH OL 3v 18 2v ­6 PROTECT SHORT TEMP STATUS ­9 26 8 28 ­20 ­20 ­9 14 ­6 16 24 20 22 INTERNAL STATUS ­3 ­3 OL GAIN/dB GAIN/dB CH CH CH 3v 1 2 ON 1 2 18 20 22 2v 16 24 14 26 8 28 OFF 0 0 0 0 30 1v 30 1v SIG SIG SENSITIVITY CH 1& 2 COLD HOT SENSITIVITY 1. 23v (+4dBu) 1. 23v (+4dBu) POWER TM CAUTION TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE. REFER SERVICING TO QUALIFIED PERSONNEL. WARNING: SERIAL NUMBER MANUFACTURING DATE 1 CHANNEL / BRIDGE / MONO LOW CUT FILTER BALANCED OR UNBALANCED STAGE MONITOR AMP MODE CHANNEL STEREO TYPICAL RISK OF ELECTRIC SHOCK DO NOT OPEN AVIS: RISCQUE DE CHOC ÉLECTRIQUE -- NE PAS OUVRIR UTILISE UN FUSIBLE DE RECHANGE DE MÊME TYPE. DEBRANCHER AVANT DE REMPLACER LE FUSIBLE TYPICAL 35 Hz INPUT MONO BRIDGE INPUT BALANCED OR UNBALANCED LOW CUT FILTER TYPICAL 35 Hz 2 STAGE MONITOR REPLACE WITH THE SAME TYPE FUSE AND RATING. DISCONNECT SUPPLY CORD BEFORE CHANGING FUSE (MONO BRIDGE) 1200 WATTS 4 OHM LOAD MIN. [. . . ] 63Hz is located at about 1 o'clock and 125Hz is about 4 o'clock. If you want to be really accurate, you will need to use a variable-frequency signal generator along with a frequency counter and a voltmeter or oscilloscope to find the exact position for the knob. The voltmeter or o'scope should be capable of measuring low frequencies accurately (down to 60Hz). Connect the signal generator to the INPUT of the amplifier and monitor the SPEAKER OUTPUT with the voltmeter or o'scope. 2. Adjust the signal generator level so you measure 1V rms output at 1kHz. (You should turn down the GAIN knobs on the amplifier about halfway. ) 3. Change the frequency of the signal generator to 63Hz or 125Hz, whichever you're using as your subwoofer crossover frequency. You may need to use a frequency counter for accuracy. Adjust the LOW CUT FILTER control until the voltmeter or o'scope reads 0. 707VAC rms. This is the ­3 dB point, and means you have now matched the LOW CUT FILTER frequency cut-off point to the SUBWOOFER FREQUENCY switch setting (either 63Hz or 125Hz). After you've completed this exercise, you should mark the position of the control with a stick-on arrow or label so you don't have to repeat it should the control accidentally get moved. 22 GENERAL PRECAUTIONS AND CONSIDERATIONS RACK MOUNTING The M·1200/M·1400 amp requires two rack space units (2U = 3. 5"). It also requires 16. 25" depth inside the rack, including the rear supports. When designing your rack, put the heavier items at the bottom and the lighter items toward the top. Secure the front panel of the amplifier to the front of the rack using four screws with soft washers to prevent scratching the panel. In addition, because of the weight of the amplifier, you must secure the rear support brackets of the amplifier to the back of the rack. You could use a support rail or shelf across the back of the rack, or angle brackets attached between the rear support brackets and the rear rails of the rack. This is recommended for all components mounted in a rack that is going to be moved frequently (or thrown in the back of a pickup truck and transported down a bumpy gravel road to that outdoor festival!). AC POWER CONSIDERATIONS Be sure the M·1200/M·1400 is plugged into an outlet that is able to supply 120VAC at high current. If the voltage should drop below 116VAC, the M·1200/M·1400 will no longer be able to supply rated power. (It will continue to operate down to 50% of the rated voltage, but it just won't be able to reach full rated power. ) Be sure the AC outlet can supply enough current to allow full power operation of all the amplifiers plugged into it. The outlet should be a three-prong socket that matches the power cord. WARNING: Bypassing the plug's ground pin can be dangerous. The AC current demand of an amplifier varies depending on several factors, including the crest factor and the duty cycle of the program material. [. . . ] For instance, four 8-ohm speakers, connected in parallel, will equal 2 ohms (8 / 4 = 2). If the loads aren't all the same, the formula gets a little more complicated, but nothing that you can't do with a simple calculator. ZT = 1 1+1+1+ . . . Z1 Z2 Z3 There are other, more complicated configurations, like series-parallel (using a combination of series and parallel links to arrive at a desired load) and parallel configurations of unmatched loads (usually not recommended). But rather than get too deep into this, let's just summarize the basics, as they apply to you and your M·1200/M·1400 Power Amplifier: · As a load gets "heavier, " its impedance in ohms decreases. [. . . ]