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MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP KIT ASSEMBLY & REPAIR FOR SALE MISCELLANEOUS VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com BUSINESS FOR SALE Well known Australian electronics company for under $50,000. GENUINE BUYERS ONLY Phone: 0410600330 LOOKING FOR: Set of Dick Smith Electronics catalogues from 1975-1982. Must be in pristine condition. Will pay $200 for the set (inc. postage), only one set needed. Contact Melanie (on behalf of inquirer on 02 8832 3100) DAVE THOMPSON (the Serviceman from S ILICON C HIP) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects like audio, video, programming etc. Many of them are in poor condition. Some of the books may not be for sale, but the vast majority are available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Silicon Chip silicon<at>siliconchip.com.au PCB PRODUCTION PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, ad­ dress & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. to be used as ‘signal’ diodes, we suggest that you change D3 to a 1N4148 or 1N5819 (both of which should switch much faster). That design really should have incorporated a buffer from the anode of D3 to pin 8 of CON2, so that RS-232 cable capacitance doesn’t slow down these transitions. Clipping indicator wanted I was wondering if Silicon Chip siliconchip.com.au has ever produced a clipping indicator project that could be added to most power audio amplifiers. (M. J., via email) • We published a Clipping Indicator circuit in the Circuit Notebook section of our November 2003 issue (siliconchip.com.au/Article/4810). However, that circuit only monitored for clipping during positive excursions. More recently, our Ultra-LD Mk.4 amplifier design from August 2015 Australia’s electronics magazine incorporated a bidirectional clipping detector. That part of the circuit was presented separately (in Fig.2 on page 36) and could be added to any power amplifier. That circuit is a little more complex but has the advantage that a single LED indicates clipping at either extreme. It’s designed to suit an amplifier with a Darlington output stage, but can easily be changed to suit other designs by choosing different voltage zener diodes for ZD1 and ZD2. SC April 2020  103