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Summary

This video delves into the evolution of amplifier technology, exploring various amplifier classes from A to TD. It covers the unique features, advantages, and limitations of each class, including Class A's low distortion but inefficiency, Class B's high efficiency with crossover distortion, and Class D's remarkable efficiency with potential sound quality issues at high frequencies. The video also highlights innovations like Class AB, Class H/G, and the groundbreaking Class GB, which optimize efficiency and reduce distortion. Finally, it introduces Class TD, a combination of Class AB and D for top performance, albeit at a higher cost.

Takeaways

• 😀 Class A amplifier uses one transistor to amplify both positive and negative phases, resulting in high power loss and heat, with an efficiency below 30%.
• 😀 The advantage of Class A amplifiers is the minimal distortion in the output signal, but their inefficiency and excessive heat generation are significant drawbacks.
• 😀 Class B amplifiers use a pair of transistors for each phase (NPN for positive and PNP for negative), which improves efficiency to 79%, but introduces crossover distortion.
• 😀 Crossover distortion in Class B amplifiers occurs due to uneven or imbalanced cutoff voltages during transistor switching.
• 😀 To address crossover distortion, engineers combined Class A and Class B designs into Class AB, which maintains better clarity and efficiency than Class B while reducing heat compared to Class A.
• 😀 Class AB amplifiers have a biasing system that keeps transistors slightly on during transitions, offering a middle ground between Class A and Class B.
• 😀 Class H or G amplifiers use a voltage stepping circuit, adjusting the voltage applied to the final transistors based on input signal strength, improving efficiency.
• 😀 In Class H or G, multiple voltage levels (e.g., 45V AC and 65V AC) are used to optimize power delivery and minimize power wastage.
• 😀 Class H or G amplifiers are more efficient than Class AB but may still suffer from distortion during voltage switching transitions.
• 😀 Crown's Ground Break (GB) system uses an inverted input to create an active ground for the amplifier, doubling the output voltage without needing a center-tapped transformer (CT).
• 😀 Class D amplifiers operate using a switching MOSFET system, resulting in minimal heat generation and high efficiency, but struggle with high-frequency linearity, especially in achieving clean sinusoidal outputs.
• 😀 Class TD amplifiers combine the benefits of Class AB and Class D, offering high efficiency, low heat, and excellent sound quality, though they are expensive and complex to repair.

Q & A

What is a Class A amplifier, and what are its advantages and disadvantages?

A Class A amplifier uses a single transistor to amplify both positive and negative phases, resulting in a 360° conduction angle. Its main advantage is minimal signal distortion, but it has high power loss and generates excessive heat, making it inefficient with an efficiency of less than 30%.

How does a Class B amplifier work, and what are its key benefits and drawbacks?

A Class B amplifier uses a pair of transistors (NPN and PNP) that work alternately to amplify positive and negative phases, with a conduction angle of 180°. It operates efficiently with an efficiency of 79%, but it introduces crossover distortion due to imbalances at the transition between transistors.

What is the purpose of combining Class A and Class B amplifier technologies into a Class AB amplifier?

Class AB amplifiers combine the strengths of both Class A and Class B amplifiers by using a push-pull configuration with added diodes at the base of transistors. This reduces crossover distortion while improving efficiency compared to Class A, resulting in better clarity and improved efficiency over Class A amplifiers.

What are the advantages and disadvantages of Class AB amplifiers?

Class AB amplifiers offer improved clarity over Class B amplifiers and better efficiency than Class A amplifiers. However, they still waste some power as heat when producing high power, making them less efficient than ideal designs.

What is the purpose of the Class H or G amplifier design, and how does it improve efficiency?

Class H or G amplifiers improve efficiency by incorporating a voltage stepper circuit. This allows the amplifier to adjust the voltage supplied to the transistors based on the input signal, ensuring that only the necessary voltage is provided, thus optimizing efficiency. This reduces energy wastage compared to traditional Class AB designs.

How does the Class G or H design achieve higher efficiency compared to Class AB amplifiers?

Class G or H amplifiers achieve higher efficiency by using multiple voltage levels for the power supply. The stepper voltage circuit adjusts the final voltage according to the input audio signal, allowing for more efficient power usage and reducing power loss and heat generation.

What is the Ground Break (GB) system introduced by Crown, and how does it differ from Class AB?

The Ground Break (GB) system used by Crown in amplifiers is based on Class AB technology but utilizes two power amplifiers, with one amplifier's input inverted. This system eliminates the need for a center-tapped transformer and enables a unique ground configuration that doubles the output voltage, providing more efficient power transfer and eliminating crossover distortion.

How does the GB system improve output voltage without affecting speaker load?

The GB system inverts one amplifier's input and creates an active ground, which causes the output voltage to be twice as large while keeping the speaker load unchanged. This system ensures that the amplifier can drive speakers at the intended impedance without the need for complex configurations like BTL (Bridge Tied Load).

What is the Class D amplifier, and what makes it highly efficient?

Class D amplifiers convert the input signal into a square wave using a comparator and then amplify it with a power amplifier. A low-pass filter converts this signal back into a sinusoidal output. The use of switching MOSFETs rather than transistors makes Class D amplifiers highly efficient, producing minimal heat and requiring smaller heatsinks.

What is the challenge faced by Class D amplifiers at high frequencies, and how do engineers address it?

Class D amplifiers struggle with achieving linearity at high frequencies due to limitations in their switching circuits. Engineers address this by improving the driver circuits and converter modules to enhance the amplifier's ability to handle high-frequency signals while maintaining a clean output.

What is the Class TD amplifier, and how does it combine features from Class AB and Class D?

Class TD amplifiers combine the features of Class AB and Class D amplifiers by using a Class AB configuration with an added adjustment regulator, similar to Class G or H. This design includes PWM control from Class D to efficiently manage voltage levels, providing high efficiency, minimal heat generation, and good sound clarity.

What are the advantages and drawbacks of Class TD amplifiers?

Class TD amplifiers offer high efficiency, minimal heat generation, and excellent sound quality. However, they are more expensive and require more complex repairs compared to other amplifier types.