Audio Power Amplifiers - towards inherently linear amplifiers
Many audio power amplifiers measure the same, yet it is claimed they sound different - so maybe we don't measure the right things? Maybe there is something internal to an amplifier that makes a difference yet is hidden for our usual distortion analysers by the ubiquitous feedback loop?
Dr. Arto Kolinummi decided to check it out and started a project to design an amplifier that is inherently linear, before the application of feedback.
This book documents his adventure which was very successful - an amplifier that challenges the linearity, open loop, of the best low distortion high feedback amps on the planet. Not that he has anything against feedback - you can still wrap it around his amps and get a performance that is literally out of this world, but it is not necessary. Does it sound better? Arto has not performed any scientific listening tests although he is convinced that inherently linear amplifiers do sound better, in general. Be that as it may, this book is a treasure trove of ultra-linear circuits, from (balanced) input stages to voltage amplifier (or transimpedance) stages to output stages. The book also has extensive information on many different ways a signal can be distorted, how to measure it, and most importantly, how to avoid it.
If you are seriously interested in audio power amp design, check it out.