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Contents Vol.24, No.4; April 2011 SILICON CHIP www.siliconchip.com.au Features 14 Can Earthquakes Be Predicted By VLF Radio Signals? Low-frequency RF signals may indicate the onset of earthquakes. Here’s a lowfrequency preamplifier that plugs into your PC’s sound card – by Stan Swan 22 The Rise & Fall Of Electronics Today International Launched 40 years ago this month, “Electronics Today” (later ETI) caused quite a stir at the time and gave “Electronics Australia” a run for its money. The magazine’s founding editor tells its story – by Collyn Rivers 70 Review: Agilent’s InfiniiVision 4-Channel Oscilloscopes Portable Headphone Amplifier For MP3 Players – Page 28. These new high-performance scopes from Agilent feature a wide screen format, have a good range of facilities and are easy to use – by Nicholas Vinen Pro jects To Build 28 Portable Headphone Amplifier For MP3 Players Fed up with the sound from your MP3 player? Build this high-quality portable headphone amplifier and be amazed at the difference – by Nicholas Vinen 40 Fixing Transformer Buzz In The Class-A Amplifier Quite a few constructors have had problems with transformer buzz in the 20W Class-A Stereo Amplifier. The cure is surprisingly simple – by Leo Simpson 44 Cheap’n’Simple 100V Speaker/Line Checker This simple project will be a boon to anyone setting up 100V PA systems. It lets you check each PA speaker and line as it is run – by Ross Tester Fixing Transformer Buzz In The Class-A Stereo Amplifier – Page 40. 62 A Speed Controller For Film Projectors Transfer your old home movies to DVD before it’s too late! This simple PICbased speed controller lets you synchronise the film frame rate with your camcorder to avoid serious flicker – by John Clarke 86 The Maximite Computer, Pt.2 Last month, we introduced our new PIC-32-based microcomputer and gave the circuit details. Now for the fun part: building it (and yes, Altronics has kits) – by Geoff Graham Special Columns Cheap’n’Simple 100V Speaker/ Line Checker – Page 44. 44. 57 Serviceman’s Log Thanks for the dodgy memory (not) – by the Serviceman 77 Circuit Notebook (1) Mains Timer For Battery Chargers; (2) Chirp Suppressor For A Car Alarm; (3) PIC-Based Square-Wave Generator; (4) H-Bridge Circuits For Robotics; (5) LED Light Controller PIC-Based Speed Controller For Film Projectors – Page 62. 94 Vintage Radio The 1939 STC 504 5-valve table radio – by Rodney Champness Departments   2   4 27 91 Publisher’s Letter Mailbag Book Review Order Form siliconchip.com.au 99 Ask Silicon Chip 102 Notes & Errata 103 Market Centre April 2011  1