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SILICON SILIC CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Stan Swan Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Warwick Farm, NSW. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au Publisher’s Letter An amplifier to warm the cockles of your heart Doubtless we will have again divided the readers of SILICON CHIP with a controversial article this month. Some will love the Currawong valve amplifier presented in these pages (with more articles to come) and some will inevitably see it as a pointless exercise and so “last century”. Even some of those readers who are keen on valve amplifiers will doubtless find something to criticise, such as the fact that it has negative feedback, or not enough feedback, or not enough power from the tetrodes, or whatever. For our part, we see it is another interesting design exercise, whether it is based on thermionic or solid state devices. Indeed, we have used a mixture, with valves being used for the signal path, to give that all-important “valve sound” and with solid-state devices used in the power supply and infrared remote control. We don’t think too many potential builders will be put off by the fact that it has an infrared remote volume control though; quite the opposite. As with any design exercise, there are compromises on many aspects. If cost was no problem, we could have produced an amplifier with a lot more power and possibly a little less distortion. But we have to be realistic, knowing that a sky-high cost will make the unit unattractive to the vast majority of readers who might like to build a modern valve amplifier. Of course, the over-riding reason why we have designed and presented the Currawong amplifier is that we realise that there is considerable interest in valve amplifiers and “valve sound”, even if we do believe that the best solid-state amplifiers are far superior to any valve design. A quick look at the performance graphs on pages 33, 37 & 38 will show that is the case, on the raw figures. Our Tiny Tim amplifier (SILICON CHIP, October & December 2013, January 2014) is a better performer and much cheaper to build. For valve aficionados though, raw figures are of little interest. Indeed, Allan Linton-Smith, one the proponents of the Currawong, demonstrated an early hard-wired prototype together with our 15W Class-A Stereo Amplifier to an interested group and he reported that most people present preferred the sound of the valve unit. Heresy! Cynically, I just think it can’t have been a very good demo; if I had done it, the preferences would have been entirely the other way! Well, OK, maybe not entirely the other way. Of course, much of the attraction of valve amplifiers relates to the fact that they are inherently simpler technology and for many people they are nostalgic – a throwback to simpler past. Solid-state amplifiers don’t glow in the dark, do they? Much the same can be said of the resurgence in interest in vinyl records and turntables. In many ways, there is more satisfaction in selecting a record to play, reading the sleeve notes, putting the disc on the turntable and then very gently placing the stylus of the cartridge into the lead-in groove – and then it begins to play. By contrast, playing a CD or pressing a button to select a digital sound track is a cold and impersonal process. So there is considerable attraction in old technology and that is why we finally decided to do the work involved in presenting the Currawong. It has not been an easy task to produce it. So even if you regard valve amplifiers as an anachronism and out of place in a magazine called SILICON CHIP, have a read through the article this month and those to come. It is a most interesting exercise and one which makes us realise that those designers from so many decades ago really did achieve very good results with such simple technology. Leo Simpson ISSN 1030-2662 Recommended and maximum price only. 4  Silicon Chip siliconchip.com.au