Learning About Class A Amplifiers - Links & Resources Provided

In summary, this site provides a good overview of the Nelson Pass amplifier and other class A amplifiers. The site also includes a build guide and forum for discussing amplifier builds.
  • #1
imsmooth
139
12
I have been reading various online tutorials on the subject. Does anyone have some good links they will share. I am trying to build my understanding of the class A amp so I understand what I am doing if I chose to build a Nelson Pass Amplifier.

I have an understanding of transistors and basic topologies already.

Thanks.
 
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  • #3
imsmooth said:
I have been reading various online tutorials on the subject. Does anyone have some good links they will share. I am trying to build my understanding of the class A amp so I understand what I am doing if I chose to build a Nelson Pass Amplifier.

I have an understanding of transistors and basic topologies already.

Thanks.

Class A refers to using single transistors (or tubes) in the single path to cover the entire dynamic range (positive and negative) of the signal for power amplification. See wikipedia:

http://en.wikipedia.org/wiki/Electronic_amplifier#Power_amplifier_classes

From what I've seen of his (Nelson Pass) design docs (below), it's basically a pretty standard Op Amp design implemented in discrete devices.

http://www.passdiy.com/pdf/classa_amp.pdf

It's using a differential pair to cover the + and - phases but the rest is a cascade of pretty traditional single-ended class A stages until you get to the Q9-Q16 which are actually Class B or AB drivers.

Again, pretty typical of how Op Amps are design and how most IC-based power amplifiers are designed. Note that the date of first Nelson Pass Class A is 1977, which is when IC Op Amps were still fairly new as a standard electronic part. Compare his design to a familiar Op Amp circuit like a 741:

http://www.national.com/ds/LM/LM741.pdf [Broken]

This picture may be helpful in visualizing what I'm describing above:

http://upload.wikimedia.org/wikiped...0050626193617!Opamptransistorlevelcolored.png

Dark Blue - input differential pair CC-CB cascode
Red - current mirrors for biasing
Magenta - darlington gain cell with feedback
Green - CB amplifier/level shifting (cascode with gain cell)
Light Blue - class AB output driver
 
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  • #4

What is a class A amplifier?

A class A amplifier is a type of electronic amplifier that operates by using the entire input signal to drive the output, resulting in minimal distortion but also high power consumption.

How does a class A amplifier work?

A class A amplifier consists of a transistor or multiple transistors that are biased to operate in the linear region, where the input signal is amplified without any cutting off or clipping. This allows for a faithful reproduction of the input signal, but also results in a constant power consumption regardless of the input signal.

What are the advantages of using a class A amplifier?

Class A amplifiers have the advantage of producing high-quality, low-distortion output signals. They also have a simple design and can be easily implemented in circuits. Additionally, they have a wide frequency response and are relatively stable.

What are the disadvantages of using a class A amplifier?

The main disadvantage of using a class A amplifier is its high power consumption. This results in a lot of wasted energy, making it inefficient for certain applications. They also tend to be larger and heavier than other amplifier classes.

What are some resources for learning more about class A amplifiers?

Some resources for learning more about class A amplifiers include online tutorials, textbooks on electronics or audio engineering, and technical articles or papers. You can also consult with experienced engineers or attend workshops or seminars on the topic. Some useful websites include All About Circuits, Electronics Tutorials, and Audioholics.

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