Mackie M800 Owner's Manual - Page 10
Feature Descriptions - stereo power amp
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00 00 00 FEATURE DESCRIPTIONS LET'S TWIST A GAIN GAIN/dB 3v 16 18 20 2v 14 22 12 24 These are completely independent volume controls for each channel. Instead of having an arbitary scale, they are carefully calibrated: • The inner ring graphic is labeled in dB, though this indicates the amplifier's voltage gain, 6 26 think of it as increasing decibels from off to 28. 28 • The outer ring shows the input sensitivity 1v SENSITIVITY 1.23v (+4dBu) in volts. This is the amount of voltage required from a mixer to drive the amp to it's rated power output (225 watts into 4 ohms). With the control fully clockwise, it will require an input level of 1.23 volts rms to reach rated power. This is equivalent to putting in a signal level of +4 dBu. If you have the knob set at 3v, it will require 3 volts from your mixer to reach full power. This will rob the mixer of headroom, because it takes extra voltage to drive the amp. Rotating the knob to 2v means you will need 2 volts from your mixer, which improves the mixer headroom. Rotating the GAIN control all the way clockwise provides the best mixer headroom under normal operation. Note: The calibration marks only apply to stereo or mono operation using speakers of 4 ohms impedance. Like all amplifier controls, you'll typically determine the optimal settings during installa- tion or sound check, then leave them alone, using your signal source (mixer/preamp) to control listening levels as you work. Or play. You may wonder why we didn't use just one stereo control to control both sides. That's in case your application requires a left/right im- balance (due to an irregularly shaped room), an irregularly shaped friend, or if you're using the two sides for completely different purposes (such as monitor in CH 1 and side-fill in CH 2). Here are some more examples of how you might use the GAIN controls: • When you are in a small room where loud volume is not required, having the amp gain controls turned fully clockwise would require you to keep the mixer faders down exceptionally low. In this case, first set the mixer faders to unity gain, adjust the mixer's input trim controls to optimum, then rotate each M•800 GAIN control until the desired volume is obtained. • If you have high efficiency speakers and a high gain preamp, you may hear "hiss" in your speakers. This can be fixed by turning the GAIN controls down a few notches. • If you are not blessed with a mixer or preamp, it is possible to connect a source component directly to the amplifier. For example, you can connect a CD player directly to the inputs. You MUST make sure that the amplifier GAIN controls are turned down before you start the CD, then bring them up to a nice level. This direct connection only applies to line-level components. It does not apply to turntables, microphones, or instruments, as these need preamplification and equalization. The GAIN controls differ in operation between stereo, dual mono, and bridged modes: STEREO and MONO: Each control is independent; CH 1 GAIN only changes CH 1, CH 2 GAIN only changes CH 2. BRIDGE: Only the CH 1 GAIN control will work because the CH 2 control is bypassed internally. FULL SYMMETRY DUAL DIFFERENTIAL HIGH CURRENT DESIGN CH GAIN/dB 1 3v 16 18 20 SIG OL -3 OL -3 14 2v 22 -6 -6 12 24 -9 -9 6 26 28 1v SENSITIVITY 1.23v (+4dBu) -20 -20 CH STATUS 1& 2 NORM HOT GAIN/dB CH 3v 16 18 20 2 2v 14 22 12 24 6 26 28 1v SENSITIVITY 1.23v (+4dBu) 10 PROFESSIONAL POWER AMPLIFIER ON OFF POWER