QSC Audio 1400, 1100, 1700, 1200 owner manual Speaker Connections, Mono Bridge Precautions

Connect the amplifier input to Ch. 1 only, and use only the Ch. 1 Gain control, which now controls the entire amplifier. Do not feed another input into Channel 2. The Ch. 2 Gain control should be kept off for safety. An 8 or 16 ohm speaker load should be connected across the two red speaker terminals, using the red terminal of Ch. 1 as the “+” or “hot” terminal, the red terminal of Ch. 2 is the “-” or “common” terminal.

Mono Bridge Precautions

a.Minimum load impedance is 8 ohms, which will be the equivalent, to the amp, of 4 ohms per channel. If a four- ohm load is used, the amp will have to work very hard and may overheat.

b.Both sides of the speaker cable are “hot” or active. Be sure there is no ground or other circuit connected to either side of the speaker cable.

c.If the parallel-channel switches (#5,6, see Section 3.51) are switched on,the signal into Ch. 2 will cancel the mono-bridge signal. To prevent this, and still permit patching to additional amps, keep the Gain for Ch. 2 fully off.

3.6 SPEAKER CONNECTIONS

3.61Speaker Terminals Red and Black 5-way binding posts, on standard 3/4-inch centers, are located on the rear of the chassis of all Series One amplifiers.

The 1100 features a pair of standard 1/4" headphone jacks on the front panel. They are connected to the speaker outputs of the amplifier through a resistive pad that prevents excessive power levels from damaging the headphones. Always fully turn down the Gain controls before plugging in headphones to prevent accidental exposure to excessive sound levels that can cause permanent hearing damage.

3.62Terminal Polarity The Red binding post carries the positive or “hot” speaker output. The Black binding post is the ground return for the speaker.

3.63Speaker Cables In order to obtain the full benefit of the high power and high damping factor of the amplifier, the user must avoid cable losses. The best way is to use the heaviest-gauge, finely stranded wiring possible. 12- gauge speaker cable is available, and heavier gauge “specialty” cable is sold by audio dealers.

3.64Cable Termination A major problem with heavy-gauge cables is that the ends are too large to fit most speaker terminals. Usually, it is necessary to install spade lugs on each end, which must be soldered or soundly crimped. These must then be screwed firmly under the binding posts. Dual banana plugs are more convenient for portable systems, and will normally accept at least 12-gauge wires.

3.65Cable Polarity Be sure to observe correct polarity at both the speaker and amplifier end. Most present-day speaker cable is color-coded or polarized in some way. Adopt a consistent wiring convention and stick to it. We suggest Black for “Com” (ground or negative) and Red for “Spkr” (hot or positive). These colors match the binding posts. By the same logic, we can assign the copper-colored wire to the Red (“Spkr”) terminal, and the silver- colored wire to the Black (“Com”) terminal.

3.66Bridged Mono Please see Section 3.52 for the bridged-mono speaker connection.

3.67Speaker Impedance The Series One amplifiers have adequate current capability to fully drive loads down to two ohms. However, many high-performance “8-ohm” loudspeakers, especially multiple-way systems with passive crossovers, have impedances at some frequencies which are far lower than the average rating. An impedance minimum of 2 ohms or less is not uncommon. For this reason, speaker impedance curves should be consulted before connecting speakers in parallel.

We would expect the amplifier to do an outstanding job with any 8-ohm, full-range speaker system, and we expect equally outstanding performance when driving 4-ohm loads without passive crossovers (as part of a bi-or-tri- amped system, for instance). 2-ohm loads should be approached with caution, as there is no further margin for impedance dips. The amp should not be damaged, but high-power operation into reactive 2-ohm loads may result in overheating or excessive AC current consumption, causing shutdowns. In addition, some power may be lost at those frequencies where the impedance dips below 2 ohms. For these reasons, operation with 2-ohm loads should be tested thoroughly before putting into use.

3.69Speaker Wire Table The following table is presented to assist in selection of appropriate speaker wire. Power losses and net damping factors (including the amplifier, with a Damping Factor of 200) are shown for a variety of lengths and gauges. Note that loss of power and damping factor are more severe for longer lengths, lower impedance loads, and higher (thinner) gauges. One should maintain a minimum damping factor of 20, and preferably 50 for high-quality systems; this will automatically prevent significant power loss. Although a power

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