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Aim of this thesis is to construct a demonstration model of a vacuum tube amplifier with a possibility of measurement of signal on more places and a possibility to see the wiring and construction of the amplifier. The first part of the work treats some important themes concerning vacuum tubes and wiring with them, for example a principle of signal intensification by vacuum tubes, categories of low-frequency amplifiers and description of several types of undesirable distortions. Next part deals with the design of the constructed amplifier, the description of the construction itself and placement of the components on the printed circuit boards and used vacuum tubes and transformers. The following part is focused on measurement of the basic properties of the amplifier and vacuum tubes by means of TESLA BM215A appliance. The final part contains technical parameters of the amplifier and photo documentation.

abstract: Efficiency of components is an ever increasing area of importance to portable applications, where a finite battery means finite operating time. Higher efficiency devices need to be designed that don't compromise on the performance that the consumer has come to expect. Class D amplifiers deliver on the goal of increased efficiency, but at the cost of distortion. Class AB amplifiers have low efficiency, but high linearity. By modulating the supply voltage of a Class AB amplifier to make a Class H amplifier, the efficiency can increase while still maintaining the Class AB level of linearity. A 92dB Power Supply Rejection Ratio (PSRR) Class AB amplifier and a Class H amplifier were designed in a 0.24um process for portable audio applications. Using a multiphase buck converter increased the efficiency of the Class H amplifier while still maintaining a fast response time to respond to audio frequencies. The Class H amplifier had an efficiency above the Class AB amplifier by 5-7% from 5-30mW of output power without affecting the total harmonic distortion (THD) at the design specifications. The Class H amplifier design met all design specifications and showed performance comparable to the designed Class AB amplifier across 1kHz-20kHz and 0.01mW-30mW. The Class H design was able to output 30mW into 16Ohms without any increase in THD. This design shows that Class H amplifiers merit more research into their potential for increasing efficiency of audio amplifiers and that even simple designs can give significant increases in efficiency without compromising linearity. / Dissertation/Thesis / M.S. Electrical Engineering 2013

Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: The class-D audio power amplifier has found widespread use in both the consumer and professional audio industry for one reason: efficiency. A higher efficiency leads to a smaller and cheaper design, and in the case of mobile devices, a longer battery life. Unfortunately, the basic class-D amplifier has some serious drawbacks. These include high distortion levels, a load dependent frequency response and the potential to radiate EMI. Except for EMI, the aforementioned issues can be mitigated by the proper implementation of global negative feedback. Negative feedback also has the potential to indirectly reduce EMI, since the timing requirements of the output devices can be relaxed. This thesis discusses the design of a clocked analogue controlled pulse-width modulated class-D audio amplifier with global negative feedback. The analogue control loop is converted to the z-domain by modelling the PWM comparator as a sampling operation. A method is implemented that improves clip recovery and ensures stability during over-modulation. Loop gain is shaped to provide a high gain across the audio band, and ripple compensation is implemented to minimize the negative effect of ripple feedback. Experimental results are presented. / AFRIKAANSE OPSOMMING: Die klas-D klankversterker geniet wydverspreide gebruik in beide die verbruiker en professionele oudio industrie vir een rede: benuttingsgraad. ’n Hoër benuttingsgraad lei tot ’n kleiner en goedkoper ontwerp, en in die geval van draagbare toestelle, tot langer batterylewe. Ongelukkig het die basiese klas-D klankversterker ernstige tekortkominge, naamlik hoë distorsievlakke, ’n lasafhanklike frekwensierespons en die vermoë om EMI te genereer. Behalwe vir EMI kan hierdie kwessies deur die korrekte toepassing van globale negatiewe terugvoer aangespreek word. Negatiewe terugvoer het ook die potensiaal om EMI indirek te verminder, aangesien die tydvereistes van die skakel stadium verlaag kan word. Hierdie tesis bespreek die ontwerp van ’n geklokte analoog-beheerde pulswydte-modulerende klas-D klankversterker met globale negatiewe terugvoer. Die analoogbeheerlus word omgeskakel na die z-vlak deur die PWM vlakvergelyker as ’n monster operasie te modelleer. ’n Metode word geïmplementeer wat die stabiliteit van die lus verseker tydens oormodulasie. Die lusaanwins word gevorm om ’n hoë aanwins in die oudioband te verseker en riffelkompensasie word geïmplementeer om die negatiewe effek van terugvoerriffel teen te werk. Eksperimentele resultate word voorgelê.

<p>The purpose with the report is to show that it is possible to design a class-D amplifier, using a programmable FPGA mounted on a developing card from Xess and a H-bridge. The FPGA was programmed in VHDL which is the language the software from Xilinx use to implement a logical function into the FPGA The logical function corresponds to a modeling of the music signal and the modeling can be described as a comparator which compare the music signal with a triangle wave and as a out signal produce a pulse width modulated (PWM) signal. The report is also a review and evaluating of two different modulating technologies, AD- modeling and BD-modeling. A detailed part about how the H-bridge was designed and how it works. The result of this project is a working audio amplifier to a significant lower price than the products in todays market.</p>

The purpose with the report is to show that it is possible to design a class-D amplifier, using a programmable FPGA mounted on a developing card from Xess and a H-bridge. The FPGA was programmed in VHDL which is the language the software from Xilinx use to implement a logical function into the FPGA The logical function corresponds to a modeling of the music signal and the modeling can be described as a comparator which compare the music signal with a triangle wave and as a out signal produce a pulse width modulated (PWM) signal. The report is also a review and evaluating of two different modulating technologies, AD- modeling and BD-modeling. A detailed part about how the H-bridge was designed and how it works. The result of this project is a working audio amplifier to a significant lower price than the products in todays market.

This thesis presents a novel three-level modulation technique for a Class-D audio amplifier, attempting to improve the poor performance of the conventional two-level modulation scheme at low input levels. The main drawback of the conventional two-level PWM (pulse-width modulation) and SDM (sigma-delta modulation) Class-D amplifier is that, with a zero input or small input, the excessively fast switching action at the output causes unwanted switching loss and switching noise, resulting in unnecessary energy waste and SNDR degradation. The presented three-level modulation circuit mainly consists of a linear feedback compensator, two comparators, and a switching logic circuit. The simulation and experimental results shows that the proposed three-level modulation s cheme outperforms the two-level sigma-delta modulation scheme in both efficiency and performance.

This work describes the design of audio amplifiers operating in switching mode. The first part describes basic principles of the power stage switching concept. There is described differences between classes of amplifiers according to technology. The second larger part includes design and construction of the switching amplifiers. Design is implemented, including the preamplifier and power supply. Power supply works in switching mode. The measured parameters of the proposed facility are given in the last part.

The aim of this work was to design and construct a simple audio amplifier, which would be based of involvement and components used in switching power sources on the maximum degree (for example from usual ATX sources for computer). The main motivation for development is the existence of many old sources that do not use and big interest of users for the construction of home audio amplifiers for small and medium power. Amplifiers based on switching power sources with greater efficiency and less weight than comparable classic amplifiers (working in classes A, B or AB). Their disadvantage is the complicated design and introduction of distortion and spurious signals to the amplified signal. This work will be described a design of simple amplifier, which will minimize these negative effects. For shortcomings and wrong parameters this proposed involvement will be eventually described and implemented design of amplifier in class D.

This diploma thesis deals with digital audio amplifier with universal inputs and its design. The first part describes modulation and audio formats for audio electronics. The thesis contain design of a block diagram of the digital audio amplifier and describes the requirements for functional blocks. As a basic device for audio signal processing was choosen integrated circuit STA326. The thesis continue with circuits design for each blocks with a description of their principles. The next section describes the construction and firmware for microcontroller. The last part of this diploma thesis is targeted on the presentation of the measured parameters of the amplifier. The conclusion summarizes the results that have been achieved and advantages and disadvantages of the digital audio amplifier prototype.