IV Speaker Protection, Background, DC Protection

that stage. Assuming that the hiss has not always been there, this indicates defective electronics. Certain special- effects units are rather noisy, so compare with other users.

Crackles— defined as a “popcorn” noise. If the crackle persists during pauses in the program material, this indicates defective electronics and must be traced down using the above procedures. Crackles which occur during audio peaks or when the electronics are vibrated usually indicate bad connections.

IV: SPEAKER PROTECTION

4.1 BACKGROUND

Speakers have several limits which should not be exceeded for reliable operation. It is the user’s responsibility to determine these limits and operate the amplifier accordingly. We offer several ways to avoid unexpected accidents, but you must still select speakers of appropriate type and power capacity and operate them within their limits.

4.2 DC PROTECTION

The design of the 1100, 1200 and 1400 amplifier circuit eliminates the DC fault problem at its source, so no special protection is required. The QSC grounded collector output circuit is AC coupled and cannot pass DC to the load. The Model 1700 features a Load Grounding™ relay and special protective circuitry to protect the load from any DC fault condition.

All Series One amplifiers feature a low frequency roll-off below 20 Hz to protect the amp and load from possible damage caused by large subsonic transients, such as breath pops, dropped microphones, etc.

4.3 HORN DRIVER PROTECTION

The compression drivers used with horns for high-frequency reproduction have special protection requirements. These devices are more delicate than large cone speakers, and more vulnerable to overload damage. In particular, the driver has a low-frequency limit which must be carefully observed. Below this frequency, the driver diaphragm can “bottom out” which will immediately alter the frequency response, and quickly cause failure. To prevent this, the user must make sure that a proper crossover network is installed.

In bi-and-tri-amp systems, where the driver is connected directly to the amplifier, the user must be especially certain that the correct frequency is used on the electronic crossover, and that no low-frequency signals, such as loud hums, get into the signal path between the electronic crossover and the power amplifier. As further protection, especially against accidental mis-adjustment or bad cables, many users install “horn protection capacitors” wired in series between the amp and driver. This part inherently blocks lower frequencies and DC, but must be selected so as not to disturb the crossover frequency. A reasonable rule of thumb is to let the capacitor roll off one octave below the intended crossover frequency. A table of values is presented below. Be sure to use non-polarized capacitors, of at least 50V rating.

Frequency	8-ohm Driver	16-ohm Driver
500 Hz	80	40
800 Hz	50	25
1000 Hz	40	20
1200 Hz	33	16
2000 Hz	20	10
3500 Hz	12	6
7000 Hz	6	3

Table 4.3 Horn Protection Capacitors. (Values in micro farads)

1200, 1700, 1400, 1100 specifications

QSC Audio has long been a revered name in professional audio, and its series of amplifiers—including the QSC 1100, 1200, 1400, and 1700—continues to showcase the brand's commitment to quality, performance, and innovation. Each model is designed to meet the diverse needs of audio professionals, whether for live sound, installations, or studio use.

The QSC 1100 amplifier is renowned for its lightweight and compact design while delivering a solid 1100 watts of power. It features QSC's advanced Class D technology, which not only provides high efficiency but also significantly reduces heat generation. The 1100 includes comprehensive protection circuitry, ensuring safe operation in all situations. With a Frequency Response of 20 Hz to 20 kHz, the amplifier offers a balanced and clear sound profile, making it suitable for various applications.

Moving up the line, the QSC 1200 offers increased power output at 1200 watts and comes equipped with advanced DSP (Digital Signal Processing). The DSP allows users to tailor the audio output precisely, delivering optimized performance for any setting. In addition to its robust power, the 1200 features a versatile input section, supporting both XLR and 1/4" TRS connectors, providing flexibility for any audio source.

The QSC 1400 amplifier is a workhorse in the series, capable of producing up to 1400 watts, making it ideal for larger venues and events. This model is designed with enhanced thermal management, ensuring reliability even during extended use. The 1400’s high-frequency response capabilities further improve its adaptability, handling complex audio signals with ease.

Lastly, the QSC 1700 stands as the powerhouse of this lineup, delivering a remarkable 1700 watts of clean, distortion-free audio. It boasts an advanced cooling system, making it perfect for high-demand environments. The 1700 is also equipped with customizable limiter settings, allowing users to protect their speakers while maintaining sound integrity.

QSC’s commitment to durability is evident in all four amplifiers, featuring rugged chassis designs and high-quality components to withstand the rigors of professional use. Collectively, the QSC 1100, 1200, 1400, and 1700 amplifiers offer a compelling range of features that cater to various audio needs, all while ensuring superior sound quality and reliability, making them excellent choices for any sound engineer or venue manager.