The Class-I Amplifier

device is biased off. In turn, when the signal goes negative, the positive device biases off while the nega- tive device turns on and conducts the negative portion of the signal.

This configuration provides much greater efficiency than class-A. The problem with class-B is that it can create distortion at the zero-crossing point of the wave- form, making it unsuitable for precision amplifier appli- cations. Improvements to and variations of class-B have been developed to solve the crossover-distortion prob- lem, and many are in common use today; however, all operate under the push-pull and time-alternation para- digms.

All amplifier classes have theoretical limits to their effi- ciency, meaning they all waste a portion of the energy they draw from the AC mains supply. Dissipative de- signs such as class-A, class-B and other variations, have theoretical limits well below those of “switching” designs since they operate in that region between cutoff and saturation. This lower efficiency may not be a particular problem with lower power applications; how- ever, it can be a major factor in large amplifiers, and when several amplifiers are being used in an applica- tion. AC mains power may be limited and/or expensive to supply, and excessive heat created by dissipative amplifiers can also be inconvenient and costly to deal with.

PWM

PWM (Pulse Width Modulation) has been used for years in non-precision amplifiers to achieve very high effi- ciency. A PWM converter modulates the analog signal onto a fixed-frequency carrier wave, creating pulses

PWM Sampling of an Analog Waveform

that vary in width depending upon the amplitude of the signal's waveform. This creates a “sampling” of the signal, which is then converted back to analog to drive the load. The output devices “switch” between fully on (saturation) and fully off (cutoff) states, so they waste very little energy.

THE TIME-ALTERNATION PROBLEM IN PWM

The primary drawback to using previously existing (class-D) PWM technology in a precision, high-power audio amplifier output stage has been that in order to keep distortion sufficiently low, accurate timing circuitry is absolutely critical. Even the slightest variation in timing can cause both positive and negative switching devices to be on at the same time, allowing high “shoot-through” current to destroy the output circuitry. In essence, the time-alternation paradigm works well for dissipative amplifiers, but not so well for switching ones.

Crown invented a highly reliable PWM amplifier output stage that produces very little audible distortion, and solves the reliability challenge. This was made possible by adapting, for the first time in amplifier design, the very opposite of time alternation.

CLASS-I OPERATION

The push-pull paradigm is part of class-I but the time- alternation paradigm is not. In class-I, two sets of switching output devices are arranged in a “parallel” fashion and operating balanced in time, with both sets sampling the same input waveform. One set is dedi- cated to the positive current portion of the waveform, and the other to the negative current portion. When there is no signal applied, or when a signal varying in ampli- tude reaches the "zero crossing" between positive and negative, the switching devices are being turned on and off simultaneously with a 50% duty cycle. The result is the formation of two balanced and canceling high- frequency output currents with no net output at the no- signal condition. The two output currents are said to be “interleaved,” and class-I is named from this interleaved characteristic.

To produce a positive output signal, the output of the positive switching device is increased in duty while the negative switching device is decreased by the same

Class-I Switches, Signal at Zero Amplitude

Page 1 Page 3
Page 2
Image 2
Crown Audio Class-I manual Pwm, TIME-ALTERNATION Problem in PWM, CLASS-I Operation, PWM Sampling of an Analog Waveform
Page 1 Page 3

Class-I specifications

Crown Audio, a leader in professional audio amplification, introduced the Crown Audio Class-I series as part of its commitment to delivering high-quality sound solutions for various applications. The Class-I amplifiers exemplify innovation in audio technology, combining advanced features with reliable performance.

One of the standout characteristics of Crown Audio Class-I amplifiers is their efficient Class-D amplification technology. This approach not only enhances energy efficiency but also reduces heat generation, allowing for a compact design without sacrificing power output. The Class-D circuitry ensures that the amplifiers can deliver high power while maintaining low distortion levels, resulting in crystal-clear sound reproduction.

The Class-I series is designed with versatility in mind. These amplifiers are capable of being used in a wide range of settings, from large concert venues to smaller installations in bars and clubs. With various power ratings available, audio professionals can select the right amplifier for their specific needs, ensuring optimal performance in any environment.

Another notable feature of the Crown Audio Class-I series is the incorporation of advanced DSP (Digital Signal Processing) technology. This technology allows users to customize audio settings and control parameters such as equalization, delay, and limiters, making it easier to fine-tune the sound to suit the venue's acoustics. The intuitive user interface further simplifies the setup process, allowing for quick adjustments during live performances.

In addition to its technological advancements, the Class-I series prioritizes durability. Built with robust materials, these amplifiers are designed to withstand the rigors of everyday use while maintaining consistent performance. The thoughtful thermal management systems incorporated into their design ensure that the amplifiers can operate in demanding conditions without overheating.

Connectivity is another area where Crown Audio excels. The Class-I amplifiers come equipped with multiple input options, including analog and digital formats. This connectivity versatility allows sound engineers to seamlessly integrate the amplifiers into existing audio systems, ensuring a smooth user experience.

Ultimately, Crown Audio Class-I amplifiers stand out in the professional audio landscape due to their combination of cutting-edge technology, flexible design, and practical features. Whether for touring professionals or fixed installations, these amplifiers promise reliable performance and exceptional sound quality, making them a preferred choice for audio engineers worldwide.
Top Page Image Contents