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For smaller, low-level systems, however, a traditional non-biamplified system should provide excellent results at a lower overall cost. Other Special Connections Many other special connections are possible on your 3000 Mixer and you will doubtless come up with your own. Please observe two precautions, however. First, watch impedances and levels carefully (see “Impedance and Level Watching” — yes we mean “watching,” not “matching”). Second, do not make a connection that forms a “feedback loop” (see example shown) as this could cause potentially damaging internal oscillations in your 3000 Mixer. A feedback loop is formed whenever you take a signal from the output of a section (such as the Program output at the Pre Amp Out jack) and feed it back to the input of that same section (such as the G-EQ In jack or even one of the Input Channel input jacks). Impedance and Level Watching Impedance Watching? Whatever happened to impedance matching? Don’t worry; impedance matching is alive and well. Most active devices, however, do not require "matched" impedances. What they do require is impedance compatibility. In addition, all audio devices require (signal) level compatibility. Thus, "impedance and level watching means establishing and maintaining that impedance and level compatibility and that’s what this section is all about. Terms: Source, Input, Output, Load In the “Origin of Terms" diagram, the microphone is the "source," the "input” is the input to the mixer/amplifier, the "output” is the output from the mixer/amplifier and the loudspeaker is the “load,1’ but these four terms are relative. For example, the input to the mixer/amplifier can be called a “load" from the viewpoint of the microphone. And, the mixer/amplifier output can be called a "source” from the viewpoint of the loudspeaker. Thus, the input impedance of the mixer/amplifier can be called the “load” impedance for the microphone and the output impedance of the mixer/amplifier can be called the ’’source” impedance for the loudspeaker. These four terms; source, input, output and load, and their relative nature are important to an understanding of impedance and level watching. As an example, consider a microphone whose “impedance" is 200-ohms. That impedance is actually the microphone’s internal impedance and should be called the microphone’s “source" or “output" impedance (the microphone is a source from the viewpoint of the mixer/amplifier). That same microphone should probably be “loaded” with an impedance of 1500-ohms or higher. That “load” impedance is actually the "input" impedance of the mixer/amplifier (the input of the mixer/amplifier is a load to the microphone). Thus, when you see any of the four terms “input, output, source or load,” try to determine the device that is being used as a reference. If it is a microphone, the "load" impedance will be a mixer or mixer/amplifier input. If the reference device is a power amplifier, the “load” impedance will be a loudspeaker. Impedance Compatibility Impedance watching just means making sure that when we connect two devices together, they are compatible from an impedance viewpoint. Here are some rules to help you "watch” your impedances: 1) Passive Devices In the special case of a passive filter, like a loudspeaker crossover network and some (rare) passive graphic equalizers, you must match impedances. These devices are the origin of the familiar term "impedance matching." Impedance matching means that if the device is a loudspeaker crossover network and it has an 8-ohm low-frequency output impedance and an 8-ohm high-frequency output impedance, then you must connect an 8-ohm low-frequency loudspeaker and an 8-ohm high-frequency loudspeaker to that crossover network. Any other impedance, either higher or lower, will degrade the performance of the crossover network. (The input to a modern loudspeaker crossover network is designed for the very low actual output impedance of a modern power amplifier.) Those increasingly rare passive graphic equalizers have similar requirements. If such a device has a 600-ohm input impedance, then you must supply a source impedance of exactly 600-ohms. The same goes for the output. If the passive graphic has a 600-ohm output impedance, then you must supply a load impedance of exactly 600-ohms to assure proper operation of the graphic equalizer. In many cases, you will have to add “build-out” and “termination" resistors to match these impedances. For information on how to go about adding build-out or termination resistors, get a copy of "Sound System Engineering” by Don and Carolyn Davis or "The Audio Cyclopedia" by Howard M. Tremaine, both published by Howard W. Sams. 2) Passive Sources Impedance watching for a passive source like a dynamic microphone or guitar pickup simply means supplying a compatible load impedance for that device. The device specifications should guide you to the proper load impedance. A good rule of thumb for dynamic microphones is t...

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