Friday, November 6, 2020

Audio Amplifier Feedback - Introduction and Contents

An apple was laying in the grass, a good apple with just a small rotten spot. The teacher picked it up and said: "There are two options. One can eat the apple as is, right away. Or one can take a knife, cut out the rot, and eat then. It would take some work, but the apple without the bad spot will be more enjoyable, and you would probably have more of it, as you won't need to avoid the rotten part. These are two different takes on anything you do." He took a knife, cut out the rotten spot and started eating. "Will you share with us?" - "No," he joked, "so that you remember".

This is the first post in a series of posts on audio amplifier feedback, written in the spirit of that parable. The focus of the series will be on the common feedback networks in audio power amplifiers and their effect on distortion and stability, with simulations and some formulas.

The contents of the series:

  1. Feedback Basics (definitions, etc.)
  2. Feedback in a Non-Inverting Amplifier
  3. Feedback in an Inverting and Differential Amplifiers
  4. Feedback in an Amplifier with Frequency Dependent Gain
  5. Feedback with Multiple Poles Inside Feedback Loop
  6. A Realistic Power Amplifier and its Phase Margin
  7. Dominant Pole (Miller) Compensation
  8. Limitations of Dominant Pole Compensation
  9. Nested Feedback Loops
  10. Input Stage Linearity
  11. Transient Intermodulation Distortion (TIM)
  12. Two-Pole Compensation
  13. NCore style compensation
  14. LTP with Frequency Dependent Load
  15. LTP with LR compensation
  16. Lead Compensation
  17. Rate-of-Closure (ROC)
  18. Lag Compensation
  19. Lead-Lag Compensation
  20. Estimating Poles in Lead-Lag Compensation Scheme
  21. Hawksford's Error Correction (
  22. Hawksford's Error Correction and "Distortion Selector"
  23. High Precision Composite Opamps