DA&T K-200 Power Amplifier User Manual
Foreword
As the world progresses, the development of ideal amplifiers should not be limited to Class A. Defining an 'ideal amplifier' depends on its application. For high-end home audio, factors like efficiency, power consumption, size, and heat are secondary. The primary criterion is 'good sound'. What constitutes 'good sound' involves system matching and subjective judgment, making it an endless pursuit. While the world may seem complex, patterns emerge upon closer observation. Just as cassette tapes and vinyl records are no longer considered the pinnacle of music carriers, digital technology and cloud computing have advanced remarkably. Similarly, amplifier technology is evolving; we are now in the era of PWM amplifiers (Class D amplifiers).
Pulse Width Modulation (PWM) Power Amplifier
Generally known as Class D amplifiers, they employ a circuit architecture distinct from Class A, Class B, or AB types, leveraging the switching characteristics of transistors. Class D amplification utilizes Pulse Width Modulation (PWM) technology. The audio signal is converted into a waveform of pulses with varying voltage amplitudes and widths. A low-pass filter then restores the original signal waveform. Its origins trace back to the invention by British scientist Alec Reeves in 1950. Following the existing naming convention of Class A, B, and C amplifiers, it was naturally designated as Class D. The primary technology employed in Class D amplification is Pulse Width Modulation (PWM), conceptually similar to switching power supplies. It operates by fully switching transistors between their on and off states, contrasting with conventional amplifiers that utilize the transistor's linear region. Essentially, Class D amplifiers continuously switch transistors, akin to digital 'zero' and 'one' states. However, the original naming did not equate Class D with digital. Therefore, it is advisable to avoid directly associating modern Class D amplifiers with digital amplification to prevent conceptual confusion. The accurate understanding is that Class D amplifiers are PWM Pulse Width Modulation amplifiers.
Diagram: PWM Amplifier Signal Path
A block diagram illustrates the signal flow: Comparator → Driver → Switching Transistors → Filter → Speaker. Above this, a graph shows a sinusoidal 'source signal' and a corresponding 'PWM signal' composed of pulses whose width varies according to the source signal's amplitude. (Cited from Wikipedia)
Evolution of Class D Amplifiers
In its early development stages, Class D amplifiers indeed exhibited less-than-ideal sound quality (distortion). From 1960 to 2000, compared to the more mature technologies of Class A, AB, or dynamic A amplifiers, Class D amplifiers, while offering advantages in heat management and efficiency, found it challenging to match the sound quality of traditional amplifiers. However, the world is in constant flux. Over the past one to two decades, the demand for enhanced listening experiences in mobile devices, coupled with technological integration, has driven the need for more compact and efficient electronic products. This shift has spurred significant advancements in Class D amplifier technology over the last ten to twenty years, focusing on improving efficiency and reducing distortion. Consequently, modern Class D amplifiers can now compete with, and in some cases surpass, traditional power amplifiers in sound quality.
Technical Advancements in Class D
The primary factors contributing to suboptimal sound quality in early Class D amplifiers are attributed to Electromagnetic Interference (EMI), modulation techniques, precise timing control for switching transistors, power supply coupling, and the stringent requirements of output filter components. By understanding these issues, comprehensive solutions can be implemented to advance Class D amplifiers. This includes employing spread-spectrum modulation techniques for signal modulation and optimizing triangle waves to minimize their inherent non-linear distortion. Furthermore, utilizing PWM power management supplies and integrating high-power anti-coupling circuits between the power amplifier and the power supply can enhance performance. To further reduce distortion, increasing open-loop gain and implementing negative feedback are effective strategies. Additionally, the use of custom-designed low-distortion, low-magnetic-saturation output filter components, coupled with precise PCB manufacturing processes that ensure optimal transistor driving timing and multi-layer construction, are crucial. The K221 power module, for instance, achieves a distortion level as low as 0.005% and delivers a mono output of 500 watts.
Block Diagrams of Amplifier Stages
Two similar block diagrams depict amplifier stages, each comprising: Comparator → Driver → Switching Transistors → Filter → Speaker. One diagram also includes a 'Feedback circuit' and a 'Triangle wave generator'.
More Than Just Grounding Isolation
Through DA&T's Digital Data Stream (DDS) technology, the Q series has achieved full digital grounding isolation. This ensures that the signal and ground lines of each unit within the Q series are completely separated. The significance of grounding quality in high-end audio system construction is well-established. Grounding isolation is a critical technique that enables each functional unit to operate independently, preventing inter-unit wiring from transmitting EMI interference. To understand this better, EMI (Electromagnetic Interference) is a form of electromagnetic wave interference that affects other systems via two primary pathways: radiative coupling (transmission through non-conductive materials via air) and conductive coupling (transmission through conductive paths like wires, including power, input, output, and inter-system connections). Many aim to eliminate EMI noise via the power plug's grounding wire. This requires the ground connection to earth to have zero impedance, an ideal that is practically unattainable. Consequently, any ground impedance will prevent complete EMI noise elimination, with higher impedance leading to reduced noise reduction. Audio systems are interconnected via signal cables, which invariably include ground lines. This ground line transmission, combined with the absence of absolute EMI elimination in connected devices, allows EMI noise to propagate throughout the entire audio chain. Grounding isolation technology breaks the ground chain between devices, effectively disrupting EMI propagation through wiring. Following the successful implementation of digital grounding isolation in the Q series, DA&T has now applied this technology to its PWM power amplifier modules, substantially mitigating EMI's detrimental effects on sound quality.
K Series Planning
For the K-422, we designed it for direct digital input Bi-Amp speaker driving, enabling the ideal operation of individual speaker unit control. However, since not all high-end speaker cabinets feature Bi-Wire terminals, two of the K-422's four power amplifier channels remain unused, leading to inefficiency. To address this, we developed the K-221, which offers both digital pre-amp output and analog pre-amp output. This allows for future Bi-Amp configurations by pairing the K-221 with the K-200. Additionally, utilizing DA&T's proprietary DDS digital transmission, it can interface with models like the Q-23 or other direct digital input power amplifiers, enabling expansion into larger Bi-Amp speaker systems. The K-200 is a two-channel analog input pure power amplifier, while the K-300 is a three-channel analog input pure power amplifier. Both incorporate grounding isolation technology and power-on linkage, facilitating easier operation for multi-channel home theater systems.
Adjustable Gain
Whether implementing Bi-Amp configurations or multi-channel home theater systems, speaker efficiency mismatches are a frequent challenge. To address this, the K series features adjustable gain for each channel, providing approximately 10dB of adjustment. This allows for straightforward balancing of efficiency differences between various speakers, enabling listeners to achieve their desired sonic balance.
Conclusion
Engineers in every era face distinct challenges dictated by the times. The PWM Pulse Width Modulation amplifier (Class D amplifier) exemplifies this. While its concept dates back over 70 years, it has experienced rapid development in the past one to two decades. Modern Class D amplifiers are vastly superior to their predecessors, driven by advancements in semiconductor technology and market demands. Development thrives where demand exists.