Bridging Precautions
Use extreme caution when operating the amplifier in the bridged mode; as potentially lethal voltage may be present at the output ter- minals. Never ground either side of the speaker cable when the amplifier is in the bridged mode; both sides are hot. If an output patch panel is used, all connections must be isolated from each other and from the panel. The recommended minimum nominal load imped- ance in the bridged mode is 4Ω (equivalent to driving both channels at 2Ω ). Driving bridged loads of less than 4Ω will activate the IGM circuitry resulting in a loss of power, and may also cause a thermal overload.
Connecting amplifier outputs to oscilloscopes or other test equipment while the amplifier is in bridged mode may damage both the amplifier and test equipment!
Switches & Controls
AC Power Switch/Circuit Breaker
The Professional Series amplifiers have a combination AC switch/circuit breaker on the front panel. If the switch shuts off during nor- mal use, push it back to the ON position once. If it will not stay on, the amplifier needs servicing. The 10001 has two AC switch/cir- cuit breakers (one for each channel); the 10004 has two, one for each
Input Attenuators
Whenever possible, set the attenuators fully clockwise to maintain optimum system headroom. The input attenuator controls (one for channel A, one for channel B) located at the front panel adjust gain for their respective amplifier channels in all modes. See the spec- ifications at the end of this manual for standard voltage gain and input sensitivity information.
When operating a Professional Series amplifier in the bridged mode, both attenuators must be in the same position so the speaker load will be equally shared between the channels. See the section on Bridged Mono Operation for more information and precautions.
Note: on the Model 7301, channel attenuators are labeled "LOWS" and "HIGHS", corresponding to the low and high frequency mon- itor output channels.
Mode Select Switch
The rear panel Mode Select Switch determines whether the amplifier is in the stereo, parallel, or bridged mono mode. Do not operate the Mode Select Switch with the amplifier powered on. See the sections on Stereo and Bridged Mono Mode for more information.
Note: On the 10004 model, there are two Mode Select Switches on the rear panel. The Model 7301 power amplifier does not have a Mode Select Switch. For more information, see the Model 7301 section.
Signal Ground Lift Jumper
In a properly designed system (for safety and to minimize noise), the amplifier should receive its ground from the AC line cord. Whenever possible, the signal source equipment should share the same AC ground as the amplifier(s). In some cases, however, this may result in a ground loop. If this happens, remove the ground lift jumper (supplied) on the rear barrier strip. This jumper electrically con- nects the signal ground (Pin 2) to the chassis/AC ground (Pin 1). If the jumper is removed, the signal ground is lifted and completely isolated from the chassis/AC ground. Do not remove the jumper if the amplifier and the signal source equipment are not on the same AC ground.
Note: On the Model 10004 power amplifier, there are two (2) signal ground lift jumpers.
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