Fullscreen HTML5Med Res (??MB)HTML4

SILICON CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Editor Peter Smith Technical Staff John Clarke, B.E.(Elec.) Ross Tester Jim Rowe, B.A., B.Sc, VK2ZLO Reader Services Ann Jenkinson Advertising Enquiries Lawrence Smith Benedictus Smith Pty Ltd Phone (02) 9211 8035 Fax: (02) 9211 0068 lawrence<at>benedictus-smith.com Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Julian Edgar, Dip.T.(Sec.), B.Ed, Grad.Dip.Jnl Mike Sheriff, B.Sc, VK2YFK Stan Swan 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 copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Noble Park, Victoria. Distribution: Network Distribution Company. Subscription rates: $83.00 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial office: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au Publisher’s Letter Some people love valve amplifiers For the many people who love valve amplifiers, our decision to publish the Mudlark A205 stereo amplifier, starting on page 30, will be warmly welcomed. At least, we hope it will. For a long time we have been asked to publish a modern valve amplifier and we have resisted, partly for the reason that no valve amplifier is a match for a well-designed solid state model, and partly because valve amplifiers have been far too expensive, especially when their modest power output is considered. So have we retreated from our belief that no valve amplifier is a match for a well-designed solid-state model? Not for a millisecond! One of the main reasons why we decided to publish the Mudlark A205 is that it is quite an innovative design and quite different from the configuration we would have used, if we had proceeded to produce a state-of-theart valve amplifier. If we had gone ahead, we would have used a class AB push-pull ultralinear output stage, probably preceded by a high voltage op amp driver, and possibly with nested feedback. We would have hoped for a power output of around 50 or 60 watts per channel. Using high quality output transformers, such a design would cost well over $1000, which is the main reason we did not proceed. By contrast, the Mudlark is a lower-powered single-ended design using two paralleled triode-connected beam power pentodes. It also does not use a conventional output transformer but uses a choke as the combined plate load for the triodes, with the output signal being capacitively coupled to a 100V line transformer. Other novel features include positive drive (class A2) via an emitter follower to the grids of the output valves and quite a complex power supply which includes protection for the valves. So the Mudlark A205 is a good design but how does its performance compare with good modern solid-state designs such as our own 15W class A design from July & August 1998 or our UltraLD 100W class AB design from November & December 2001? Well, the solid-state designs clearly beat it on every measured parameter: noise, distortion, frequency response, separation between channels and so on. Nothing has changed there. So why are we publishing the circuit and the full constructional details? Well, in spite of any apparent superiority in the measured figures of solid-state amplifiers, many people will still find the sound of the Mudlark amplifier very satisfying. And so it is. But superior to the above-mentioned transistor amplifiers? Not in my opinion. However, we think the Mudlark A205 design has considerable merit and it comes at a price which, while still expensive, is a bargain compared to many audiophile valve amplifiers available in the marketplace. So have a look at the first of the Mudlark A205 articles in this issue. We don’t agree with everything that the designer, David Whitby, advocates but we are sure that his design will provoke a lively debate. Leo Simpson ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip siliconchip.com.au