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Amplifier class of operation

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On 1/27/2021 at 10:55 AM, tube fanatic said:

Questions always arise about this topic.  Here is a nice basic overview.  Although intended for guitar amps, the rules still apply:

 

https://www.aikenamps.com/index.php/the-last-word-on-class-a

 

Maynard

 

Is there a simpler explanation out there? LOL...Tried to understand it.  
Thanks for posting though.

 

Take Care

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In class A the transistor is turned on up as high as the designer thinks is safe and operates at it's maximum safe operating point. The audio signal is then fed into the transistor. In B the transistor is turned on only when it sees an audio signal then cuts off. A/B is when the transistor is turned on a small amount always and opens up to it's safe operating point when it sees a signal. This is the reason that class A amplifiers run so hot all the time whereas a class A/B amplifier only gets really warm when playing the music loud. For this reason, the transistor operating fully running as high as safe, class A is considered the most linear operating method of amplification. The reason purist still prefer class A not that other forms of amplification can and do sound excellent when designed properly. Class D is another form which others can better explain then myself. I have a rudimentary understanding of how it works but not enough to go into detail. I hope this helps some. The article posted by Nelson is an excellent one but does require some electronic knowledge to fully appreciate. Class A, AB and D are the ones music lovers generally have to pick from. 

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Another explanation Nelson Pass has given in one of his papers is like a relay race. In class A just one runner takes the baton and runs as fast as he can and never passes the baton. In class B the first runner takes the baton and runs as fast as he can and stops and passes the baton. In class A/B it is more like a real relay race where the baton is passed with both runners slowing down and passing the baton. 

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With class D the runner rides a motorcycle?

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  • Haha 1

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33 minutes ago, DizRotus said:

With class D the runner rides a motorcycle?

Class A in the winter, class D in the summer. 

  • Haha 1

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Some may wonder how a push pull amplifier can operate in class A. How it is done is the transistor are run like SE amplifier as high as safely possible all the time instead of like an A/B amplifier where the transistor runs just a little bit and increases when a signal is detected. Most designers in an A/B amplifier just run the transistor high enough to eliminate crossover distortion. Crossover distortion occurs when the positive part of the signal goes to one transistor and then the negative part of the signal transfers to the other transistor. I intentional left out the word bias where it may be better understood in layman terms. 

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Other than the Class D nCore monos every amp I use is Class A, tubes and SS. For my ears, it’s the only way to fly — 

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Spoiler

 

Although tubes and some transistors share similar characteristics, there are sufficient differences to justify why this discussion should stay in the realm of tubes.  The SS stuff should be in the section of those “other guys.” 😀😀

 

Maynard

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