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Self on Audio
Whether you are a dedicated audiophile who wants to gain a more complete understanding of the design issues behind a truly great amp, or a professional electronic designer seeking to learn more about the art of amplifier design, there can be no better place to start than with the 35 classic magazine articles collected together in this book.Douglas Self offers a tried and tested method for designing audio amplifiers in a way that improves performance at every point in the circuit where distortion can creep in - without significantly increasing cost. Through the articles in this book, he takes readers through the causes of distortion, measurement techniques, and design solutions to minimise distortion and efficiency. Most of the articles are based round the design of a specific amplifier, making this book especially valuable for anyone considering building a Self amplifier from scratch.Self is senior designer with a high-end audio manufacturer, as well as a prolific and highly respected writer. His career in audio design is reflected in the articles in this book, originally published in the pages of Electronics World and Wireless World over a 25 year period. * An audio amp design cookbook, comprising 35 of Douglas Self's definitive audio design articles* Complete designs for readers to build and adapt* An anthology of classic designs for electronics enthusiasts, Hi-Fi devotees and professional designers alike
eBook
The Class D Audio Power Amplifier: A Review
Class D power amplifiers, one of the most critical devices for application in sound systems, face severe challenges due to the increasing requirement of smartphones, digital television, digital sound, and other terminals. The audio power amplifier has developed from a transistor amplifier to a field-effect tube amplifier, and digital amplifiers have made significant progress in circuit technology, components, and ideological understanding. The stumbling blocks for a successful power amplifier are low power efficiency and a high distortion rate. Therefore, Class D audio amplifiers are becoming necessary for smartphones and terminals due to their power efficiency. However, the switching nature and intrinsic worst linearity of Class D amplifiers compared to linear amplifiers make it hard to dominate the market for high-quality speakers. The breakthrough arrived with the GaN device, which is appropriate for fast-switching and high-power-density power electronics switching elements compared with traditional Si devices, thus, reducing power electronic systems’ weight, power consumption, and cost. GaN devices allow Class D audio amplifiers to have high fidelity and efficiency. This paper analyzes and discusses the topological structure and characteristics and makes a judgment that Class D amplifiers based on GaN amplifiers are the future development direction of audio amplifiers.
Journal Article
Digital removal of pulse-width-modulation-induced distortion in class-D audio amplifiers
In an all-digital, class-D audio amplifier, pulse-width-modulation (PWM) of a digital signal source is usually followed by a low-order analog low-pass filter to construct the analog audio waveform. This study shows how to remove the non-linear distortion usually associated with PWM, by prefiltering the digital signal prior to the PWM mapping in such a manner that the overall result is distortion-free. The prefiltering is done using computationally effective infinite-impulse-response filters combined with short-kernel anticausal finite-impulse-response filters, and relies on the interpretation of PWM as a Volterra filter. A case study is presented where a second-order Butterworth analog low-pass filter is used for reconstruction of the analog audio signal. A complete amplifier system is modelled, including upsampling, Volterra prefiltering and noise feedback coding. Computer simulations on CD music signals were performed. Using a third-order prefilter, a signal-to-noise ratio of 97–102 dB was obtained for the music signals tested. All necessary filter data needed for realisation of the prefilter are given in the Appendix.
Journal Article
Predictive Thermal Management for Dual PWM Fans in High-Power Audio Amplifiers
This paper presents the design and implementation of a low-cost microcontroller-based dual-channel fan controller optimized for high-power audio amplifiers, yet adaptable to power supplies, electronic loads, and other thermally intensive systems. Unlike conventional designs that drive all fans uniformly, the proposed solution provides fully independent cooling via dual I2C temperature sensors, predictive trend analysis, and multi-stage hysteresis. The controller incorporates advanced features including an anti-dust startup sequence, predictive boost with latching, active cross-cooling, anti-heat-soak protection, and stall detection via tachometer monitoring, complemented by LED-based fault signaling and automatic channel muting during overheating or fan failure. Hardware support for 12 V and 24 V fans, dual power-input options, and a compact PCB layout enhance integration flexibility. The firmware employs temperature-driven PWM mapping with EMA filtering and multi-level hysteresis. The experimental results confirm that all implemented features operate as intended, with each function demonstrating clear practical relevance, whether in improving responsiveness, preventing heat accumulation, or enhancing system reliability under a wide range of operating conditions.
Journal Article
Filterless, Digital Class-BD Audio Amplifiers with Constant Common Mode Output Voltage
This paper presents new and original architectures and implementations of two filterless, open-loop digital Class-BD audio amplifiers with constant common mode (CM) output voltage. The first, low-power amplifier consists of four ultrahigh-current EL7158 pin drivers, the OUT pins of which form the H bridge. The drivers are controlled from the extended LBDD PWM modulator and have appropriately set voltage levels on the VL and VH pins. The second proposed amplifier consists of two cooperating H-bridge power stages (HBS) implemented on complementary MOSFET pairs and powered by two different voltages. Both HBSs are driven by four EL7158 pin drivers having appropriately adjusted voltage levels on the VL and VH pins and controlled by an extended LBDD PWM modulator. The hybrid 9 bit DPWM modulator uses a linearized Class-BD double-sided modulation scheme with pre-compensation, enabling the most faithful emulation of natural NBDD PWM and, thus, providing attractive spectral characteristics at the DM output. Basic SPICE simulations and experimental results of the proposed digital Class-BD amplifiers were compared with the conventional digital Class-BD amplifiers. The elimination of CM signals significantly contributes to the reduction in electromagnetic interference (EMI), particularly those produced on the cables connecting the loudspeaker to the HBS terminal. Proposed Class-BD amplifiers with original and new topologies, due to their simple design and easy control (no galvanic isolation of control signals and no floating bias power supplies), which generate no CM voltage and feature excellent DM performance, similar to conventional Class-BD amplifiers, are very attractive solutions for filterless Class-BD amplifiers.
Journal Article
Design and Development of Non-Linearly Controlled Class-D Audio Amplifier
A systematic and simple approach to develop a 20 W audio frequency range switch mode amplifier is presented in this paper. A non-linear sliding mode (SM) technique-based low cost analog controller enables the realized amplifier to deliver highly linear and efficient operation throughout the audio frequency spectrum. The theoretical aspects and practical limitations in the design and realization of subsystems, such as the signal conditioning stage, power stage and sliding mode controller, are considered, while the viable solution is also stated and justified. The hardware realization scheme is also elaborated, based on which the laboratory prototype is fabricated. Hardware results with a 4 Ω resistive load are given on which the performance of the amplifier is evaluated. The total harmonic distortion (THD) below 1% and 73% efficiency at peak load make the amplifier well suited for high quality audio application.
Journal Article
Linearized 9-Bit Hybrid LBDD PWM Modulator for Digital Class-BD Amplifier
The paper presents an original architecture and implementation of 9-bit Linearized Pulse Width Modulator (LPWM) for Class-BD amplifier, based on the hybrid method using STM32 microcontroller and Programmable Tapped Delay Line (PTDL). The analog input signals are converted into 12-bit PCM signals, then are directly transformed into 32-bit LBDD DPWM data of the pulse-edge locations within n-th period of the switching frequency, next requantized to the 9-bit digital outputs, and finally converted into the two physical trains of 1-bit PWM signals, to control the output stage of the Class-BD audio amplifier. The hybrid 9-bit quantizer converts 6 MSB bits using counter method, based on the peripherals of STM32 microcontroller, while the remaining 3 LSB bits - using a method based on the PTDL. In the paper extensive verification of algorithm and circuit operation as well as simulation in MATLAB and experimental results of the proposed 9-bit hybrid LBDD DPWM circuit have been performed. It allows to attain SNR of 80 dB and THD about 0,3% within the audio baseband.
Journal Article
A New Combined Boost Converter with Improved Voltage Gain as a Battery-Powered Front-End Interface for Automotive Audio Amplifiers
High boost DC/DC voltage conversion is always indispensable in a power electronic interface of certain battery-powered electrical equipment. However, a conventional boost converter works for a wide duty cycle for such high voltage gain, which increases power consumption and has low reliability problems. In order to solve this issue, a new battery-powered combined boost converter with an interleaved structure consisting of two phases used in automotive audio amplifier is presented. The first phase uses a conventional boost converter; the second phase employs the inverted type. With this architecture, a higher boost voltage gain is able to be achieved. A derivation of the operating principles of the converter, analyses of its topology, as well as a closed-loop control designs are performed in this study. Furthermore, simulations and experiments are also performed using input voltage of 12 V for a 120 W circuit. A reasonable duty cycle is selected to reach output voltage of 60 V, which corresponds to static voltage gain of five. The converter achieves a maximum measured conversion efficiency of 98.7% and the full load efficiency of 89.1%.
Journal Article