Protection Circuits

The design goal in high-efficiency amplifiers such as the CX Series is to increase the amplifier’s ability to deliver peak power without increasing its size, weight, and cost. However, the higher power flow through the output components makes effective, responsive protection circuitry absolutely vital. To this end, the design of the CX series takes a comprehensive approach to protection.

As in all QSC amplifiers, the inputs are resistively buffered for overload and RF protection. Chassis bypass capacitors at inputs and outputs further improve RF rejection.

CX amplifiers use the proven Ouput Averaging™ short circuit protection system. This circuit permits full output current even into resistive or reactive 2-ohm loads, but reduces the current safely by about 75% if the output is shorted.

Turn-on/turn-off muting keeps transients-both from the amplifier itself and from upstream equipment-from reaching the speakers when the amplifier is turned on or off. The turn-on delay is approximately three seconds to allow the power supplies and circuitry to stabilize. Turn-off muting occurs almost immediately after power is shut off. Muting occurs whether power is turned on and off using the front panel power switch or externally at the AC source.

Inside a CX6, CX6T, CX12, or CX12T amplifier, an NTC (negative temperature coefficient) thermistor in series with the power switch and transformer primary limits inrush current. The thermistor initially has a high resistance, which then diminishes rapidly as it warms, to avoid power loss. Typically, the inrush current of an CX Series amplifier thus is equal to that of another amplifier of about 1/3 to 1/2 its power rating. The low inrush of the smaller CX4 and CX4T does not require an NTC thermistor.

When the DC fault protection circuitry of a CX6, CX6T, CX12, or CX12T senses a DC voltage on a channel output, it actuates a relay which shorts the output and load to ground. The amplifier’s Output Averaging protection circuitry will limit current to further protect the output devices. If the DC problem persists, that channel will go into thermal protection mode and should be serviced by a qualified technician.

The output stage of a CX4 or CX4T channel has AC coupling to prevent it from passing DC.

Temperature sensors on the channel heatsinks and the power transformers are part of the thermal management circuitry. The temperature sensors govern whether the dual-speed fan should run at low or high speed. Below 55½C, the fan runs at low speed; above, it runs at high speed. At or above 85½ C, the channel mutes to go into thermal protection.

Built-in second-order 50 Hz (CX4T) and third-order 45 Hz (CX6T and CX12T) Butterworth high-pass filtering helps prevent saturation in speaker transformers on distributed lines by sharply reducing the amount of ultra-low frequency energy the amplifier puts out. However, some lower-quality speaker transformers have rated low- frequency responses that do not even extend as low as these filters; if you have any of these in your distributed line system you should insert corresponding high-pass filtering in the audio path before the amplifier.

CX Series specifications

QSC Audio, a recognized leader in professional audio solutions, presents the CX Series of amplifiers, a fusion of power, efficiency, and cutting-edge technology designed to meet the demands of various sound reinforcement applications. Known for their reliability and outstanding performance, the CX Series amplifiers are perfect for installations in venues, theaters, and houses of worship, delivering high-quality audio reproduction regardless of the setting.

At the core of the CX Series is its robust Class D amplification. This technology not only ensures excellent audio fidelity but also enhances energy efficiency, resulting in lower operational costs and cooler running temperatures. The amplifiers utilize a linear power supply, which contributes to exceptional audio quality by providing stable and clean power to the components. With varying power ratings, including options ranging from 200 to 1200 watts per channel, the CX Series caters to different venue sizes and specific audio requirements.

The CX Series is engineered with a range of features that enhance usability and performance. Integrated DSP (Digital Signal Processing) allows users to access advanced sound processing algorithms, enabling fine-tuning of audio settings for optimal performance. The amplifiers include comprehensive protection circuitry to safeguard the equipment from thermal overload, short circuits, and signal clipping, ensuring longevity and reliability in demanding environments.

Connectivity is also a significant aspect of the CX Series. The amplifiers are equipped with a variety of input and output options, including XLR, 1/4" TRS, and barrier strip connectors, facilitating seamless integration with a wide range of audio sources and speakers. Moreover, the user-friendly interface includes LCD displays for easy monitoring, making setup and adjustments straightforward for audio engineers and technicians.

Another defining feature of the CX Series is its lightweight design. This portability makes installation and transport easy without compromising on performance. Additionally, QSC’s commitment to sustainability is evident in the design, as the amplifiers are constructed with environmentally friendly materials and have a reduced carbon footprint, aligning with modern practices in eco-conscious audio engineering.

In summary, the QSC Audio CX Series amplifiers blend professionalism with versatility, delivering exceptional performance that satisfies both audio quality and operational reliability. Their innovative technologies and thoughtful design make them a powerful ally for professionals in any sound reinforcement scenario.