Listed in alphabetical order
Acoustica.org.uk is basically a scratch-pad, a useful-pot to keep things in. It's mostly about audio engineering with a DIY flavour, salted with other odd things found interesting.
Great website featuring interesting articles I find entertaining
Countless schematics and service manuals for products of many different brands. The perfect resource for anybody repairing equipment. Jan Dupont maintains this great resource free of charge.
This great website and forum offers reviews of audio gear that is based on real measurements instead of purely subjective statements and therefore highly recommended to anybody looking for solid data.
As the name implies, this website is about building audio amplifiers. There are many designs available. Most designs are pretty basic, typical DIY projects. You need to register in order to view schematics.
Countless clever circuit ideas
I like Bob's book very much. He is also very active on the DIY Audio forums.
Edmond Stuart's website. Make sure to read about his impressive PGP (Pretty Good Power Amp) project.
A great place where experienced audio enthusiasts share their ideas and knowledge.
Chris Russel's website
Impressive loudspeaker projects, especially horn loaded ones
Samuel Groner is well respected in the audio community and has written some very interesting articles. His website also features links to further interesting websites.
Features some articles about audio and many other technical articles.
This looks like a super useful collection of articles and resources. I haven't read any of them, but plan to do so.
The HiFi Engine library has images, specifications and reviews for thousands of audio components, along with owners manuals, service manuals, schematics and product catalogues for amplifiers, pre-amps, power amps, tuners, tape decks, cd players etc.
Thanks to the many visitors who have scanned documents and donated images to the gallery.
Service only after registration (free of charge)
Electromagnetic Compatibility Consulting and Training
Good electromagnetic design is relevant to all kinds of electronics and audio. I have learned a lot about EMC from studying technical articles written by Henry Ott and highly recommend this resource for education.
Welcome to over 500 posts and to over 50 articles on amplifiers, tube-based preamps, crossovers, headphone amplifiers, single-ended amplifiers, push-pull amplifiers, Circlotron circuit design, hybrid amplifiers, cascode circuits, White cathode followers, grounded-cathode amplifiers, tube series regulators and shunt regulators, the Aikido amplifier, tranformer coupling, DACs and tubes - and hundreds of vacuum tube circuits that use 6SN7s to 300Bs, all explained in careful detail.
Website by DIY Audio member Keantoken. I like his power supply rail filter very much.
Paul Kemble's website features many interesting articles and is well worth a visit.
Jan Didden's website
Jan Didden's magazine. Haven't read it yet, but believe it is excellent
Pierre has investigated a phenomenon that is not discussed often, but seems to be relevant: Memory distortion. I highly recommend studying his work.
Marc has a very helpful website featuring two e-books: One about radio telemetry systems and another about power quality issues and cures. The website also features many technical and non-technical articles worth reading. Highly recommended!
Haven't read much of this, but it seems interesting
New discovery for me in year 2021: A HiFi / High End audio magazine featuring news, equipment reviews, galleries and much more. I find this very entertaining to read.
Suzy's blog is about audio, wooden boat building, computers, electronics, lugged steel bicycle frames and other typical girls things. Suzy Impresses with outstanding craftsmanship in all of her projects. I find her blog entertaining and worthwhile reading.
Seems like another Edmond Stuart website
Online HiFi review
Free and proudly independent (no-advertising) since 1996
Collection of his ebooks, resources for CFAs, references and regulators
Some interesting projects, articles and resources. New addition to this list. I haven't read much of this yet.
Listed without any order
Spice models from Bob Cordell are well respected in the audio community. I use them almost exclusively for simulating my designs.
This small wiki describes the best setup to simulate FFT with LTSpice
This guide has helped me a lot identifying and solving any convergence issues without resorting to hacks.
Some of this may be very helpful.
Sometimes online calculators may be useful for a quick estimation. Here are some calculators I use often. Listed without any order.
This calculator from Okawa Electric Design is excellent for checking whether a L-C low pass filter design is good or not. They offer further calculators I haven'tried yet.
This is the most useful calculator for toriod inductors I have seen so far.
Sengspiel Audio offers a useful calculator for Decibel values.
Easily calculate the resistor value of any color or digit coded resistor. This is especially useful in case the resistance cannot be measured.
The best geometric calculators I found on the web including geometric forms I have never heard of before.
This collection of calculators by AJ Design is mostly for physics and economy.