3

I am a novice interested in learning amplifier design for audio projects. I can design simple "elementary" amplifiers such as CE, CB, and CC and can make them work with desired impedances, good biasing, and properly-sized coupling capacitors. I am good with basics like Ohms Law, KVL/KCL, and can do simple analysis of discrete bjt circuits. I have probably a basic understanding of transistor models like hybrid-pi. I'd like to get to the point where I can design more useful circuits with multiple stages that would actually work to drive real-life speakers, but have struggled to find a good source. I don't know what I'm missing, but when I look online for information on combining stages, power amplifiers, class AB amplifiers and the like it's clear that there are gaps in my knowledge. What is the next thing I need to learn about? And, perhaps more importantly, can you suggest a book that might meet me at my level?

nuggethead
  • 1,123
  • 6
  • 17
  • 1
    Your question will be closed soon, so before that happens, have a look at JohnAudioTech's channel on youtube and the series of videos he did on his audio amplifier. Does not require any more prerequisited than what you've listed. You need to learn about current mirros, active loads, feedback... The books by Self and Cordell might help you. – Sredni Vashtar Sep 25 '20 at 23:14
  • Why would it be closed? It seems a reasonable question to me. Self and Cordell have many publications, also -- is there one in particular that you would recommend above the others? – nuggethead Sep 26 '20 at 00:38
  • 3
    I had in mind two Douglas Self books: "Small Signal Audio Design" and "Audio Power Amplifier Design", while Cordell has written "Designing Audio Power Amplifers". I assumed you were interested in audio applications. – Sredni Vashtar Sep 26 '20 at 00:45
  • 1
    It would be closed because it is opinion based, too general, and includes a product recommendation. That said, you may find long-tailed differential pairs useful. They are what makes op-amps what they are. Also cascode might be useful. – DKNguyen Sep 26 '20 at 01:04
  • I've looked over your questions and I don't consider you to be ready to move on. You have a lot yet to gather up. But if you want to pick up something really important to this area that you may lack, I'd recommend two areas: (1) global NFB; and (2) learning how to limit the bandwidth, properly -- especially towards higher frequencies in high voltage gain situations. (Maybe eventually noise analysis. But not now.) – jonk Sep 26 '20 at 01:34
  • Thanks@jonk I've appreciated your responses to some of my previous questions. I'll look into NFB and bandwidth next. If you come across good questions and answers on SE that you think I should read, I'm all ears – nuggethead Sep 26 '20 at 01:55
  • Also, study heat dissipation and heat sinking. I am not an audio designer, but thermal management is a major part of audio amplifier design. I also think Douglas Self is very much worth reading for you. – user57037 Sep 26 '20 at 03:41
  • 1
    @mkeith I think Douglas Self and also Cordell are both worth a thorough read. However, that said, there is a certain assumption about prior knowledge by both authors. They are talking to other well-informed readers and covering a lot of those thoughts others might wonder about. But that means its less for those who are trying to work lift themselves by their own bootstraps and struggling to understand each section within the amplifier design. It's kind of assumed that you have the basics down and want to work on the important details for a real product. – jonk Sep 26 '20 at 04:43
  • 1
    I read Self after I got my BSEE. You may well be correct. Nonetheless, when one reads an advanced text and doesn't fully understand it, at least it gives one an idea about the concepts one needs to study. – user57037 Sep 26 '20 at 06:28
  • Well, clearly I do not have a degree in EE! My training and degrees are in music, very much from the other side of the brain! – nuggethead Sep 26 '20 at 10:45
  • 1
    @mkeith True enough. I often start out by reading an advanced text in order to sample the concept-space that I don't know about so that I will at least be aware of what I need to become still more aware of. ;) – jonk Sep 26 '20 at 18:59
  • That, and help from SE – nuggethead Sep 26 '20 at 20:43

2 Answers2

7

I'd suggest Field Effect Transistors as your next field of study. There are several different types and you will find widespread applications.

Phil Freedenberg
  • 789
  • 4
  • 10
5

I suggest you examine the various functions of this circuit (question asked today)

Output Stage Clipping

where

  • diffpairs are the input (PNPs) with current source

  • differential_to_single_ended converter

  • rail_to_rail gain stage

  • biasing, which is ttemperature-compensated

  • output devices that need debugging

with problems

  • greatly imbalanced source resistances into bases of the diffpairs; left transistor has 10Kohm; right transistor has (the global feedback network) 2K || 20K; these imbalances cause output DC offset voltage that will injure the loudspeaker load

  • no frequency compensation, so probably the amplifier will oscillate

  • no ZOBEL network (series R+C) on output, to help stabilize the amplifier

analogsystemsrf
  • 33,703
  • 2
  • 18
  • 46