The fourth issue of 1975 for The Audio Amateur celebrates the close of the magazine's fifth year with a heavy focus on precision test equipment, innovative room acoustics, and DIY electrostatic design. Here are the highlights:
- Morrey's Super Oscillator: Achieve laboratory-grade precision on an amateur budget. Walter Morrey details how to modify the Heath IG-18 oscillator to reach near-ideal distortion levels—as low as .0005%—making it an essential tool for high-performance audio analysis.
- A Stereo Delay Line: Bring the "concert hall" experience to your listening room. Douglas Preis provides a complete construction guide for an affordable, two-channel acoustical delay line that adds a stunning new dimension of spaciousness and reverberation to your music.
- A.L.F. Garbage Filter: Clean up your signal with this versatile general-purpose filter card. Originally conceived as a 30Hz rumble filter, audio legend Walt Jung shows how this design can be adapted to handle almost any active filter task, from crossovers to subsonic suppression.
- The Sanders Electrostatic Speaker: Experience the legendary transparency and detail of electrostatic sound. Roger Sanders provides a comprehensive, step-by-step guide to building your own full-range electrostatic panels, including the complex construction of wire stators and high-voltage polarizing supplies.
- What is PCM? Part 2: Go inside the digital revolution. Reg Williamson continues his definitive look at Pulse Code Modulation, explaining the working principles of the BBC’s advanced sound distribution systems and how digital technology ensures absolute signal integrity.
- Audio Aids: This issue is packed with technical wisdom from readers, featuring a method for measuring crossover distortion in power amplifiers and a design for a transformerless balanced output for professional-grade signal management.
- Classic Circuitry: Study the engineering of a vintage icon. This issue includes the full, detailed schematic for the Marantz Electronic Crossover, offering a valuable reference for tube enthusiasts and restorers of high-end vintage gear.
Table of Contents
- Morrey's Super Oscillator: by Walter T. Morrey ................................................................ 3
- A Stereo Delay Line: by Douglas H. Preis .......................................................................... 10
- A.L.F. Garbage Filter: by Walt Jung ................................................................................... 14
- The Sanders Electrostatic Speaker: by Roger R. Sanders .......................................... 18
- What is PCM? Part 2: by Reg Williamson ........................................................................ 30
- Audio Aids: by readers Great American Sound, James A. Mears, and others ............ 34
- Classic Circuitry: The Marantz Electronic Crossover ....................................................... 38
- LETTERS ................................................................................................................................. 40
- CLASSIFIED ............................................................................................................................. 43
- AD INDEX ............................................................................................................................... 59