Those Categories are about Audio circuits diagrams and projects. Everything from the basic amplifier of the small phono player to the high-powered auto receiver-amplifier is covered in this section. Audio enthusiasts, hobbyists, electronic students, and technicians can build high-quality audio projects as well as high-power electronic audio testing equipment, graphic equalizers, effects circuits etc. Build audio projects that produce great sound for far less than they cost in the store. The Audio projects are not tested but some of them, are top quality audio electronic projects that are based on solid science and produce fantastic sound! Some Audio circuits are: Balance control, Signal conditioning techniques, Voltage amplifiers, Preamps for home and stage, Audio Tone controls, Passive and active filters, Parametric filters ,Audio Graphic equalizers, Headphone audio amplifiers, Power audio amplifiers, Speaker protection systems, Level indicators and many more.