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Contents Vol.27, No.9; September 2014 SILICON CHIP www.siliconchip.com.au Create Eerie Music with The Opto-Theremin – Page 20. Features 12 How Omega Ruled The World Before GPS What was the main global real-time radio navigation system before GPS took over in 1997? The answer is “Omega”. Here’s a look at how the system worked – by Dr David Maddison 32 Review: Incus Bluetooth Hearing Aid Programmer Blamey & Saunders’ latest programmer for their great-value hearing aids makes them even better. You can program them yourself to suit your hearing loss and Bluetooth connection makes it easy – by Ross Tester 57 The Sydney Electronex 2014 Show & PCB Design Tips Our preview to the Electronex 2014 show (September 10-11) with an emphasis on PCB design and manufacturing 90 The Canberra RadioFest: All Types Of Vintage Radios Want the opportunity to view or purchase an impressive collection of vintage radios and spares? The Canberra RadioFest from September 19-20 is the place to be – by Kevin Poulter Pro jects To Build 20 Create Eerie Music With The Opto-Theremin, Pt.1 Completely new Theremin design uses an optical distance sensor to control volume, making it easier to play and easier to build and adjust than earlier designs. A metal antenna is used for pitch control – by John Clarke Wideband Active Differential Oscilloscope Probe – Page 40. 40 A Wideband Active Differential Oscilloscope Probe Using a scope to measure high-speed/high-frequency circuits can be tricky with a passive test probe. This high-performance active differential probe costs much less than commercial units, has very little circuit loading and has a usable bandwidth of more than 80MHz – by Jim Rowe 74 Mini-D Stereo 10W/Channel Class-D Audio Amplifier This Class-D audio amplifier module delivers more than 10W/channel in stereo mode or 30W into a single speaker in mono mode and features over-current, over-temperature, short circuit and speaker protection – by Nicholas Vinen Mini-D Stereo 10W/Channel Class-D Audio Amplifier – Page 74. 86 An Improved Tweeter Horn For The Majestic Loudspeaker The Majestic loudspeaker in the June 2014 issue has created lots of interest but the Etone tweeter horn has become unavailable. We’ve located a Celestion horn which looks and sounds even better – by Allan Linton-Smith & Leo Simpson Special Columns 34 Serviceman’s Log Cameras can be tricky to repair – by Dave Thompson 84 Circuit Notebook (1) Micromite-Based Controller For 230VAC LED Downlights; (2) Safely Measuring The Frequency Output Of The Induction Motor Speed Controller 92 Vintage Radio Pye’s excellent C-2 Jetliner transistor radio – by Ian Batty Departments   2 Publisher’s Letter   4 Mailbag siliconchip.com.au 31 Subscriptions 98 Ask Silicon Chip 102 103 104 104 Online Shop Market Centre Advertising Index Notes & Errata Improved Tweeter Horn For the Majestic Loudspeaker – Page 86. September 2014  1