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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 Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Julian Edgar, Dip.T.(Sec.), B.Ed, Grad.Dip.Jnl Kevin Poulter 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: $89.50 per year in Australia. For overseas rates, see the subscription 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 Do people really want a high-performance valve amplifier? This month’s Mailbag kicks off with a letter which is a plea for a high-quality valve amplifier. This particular reader has evidently done a lot of background research and knows many of the issues involved. And while I can understand some of the attractions of valve amplifiers – those glowing filaments and all of that – I wonder whether enough readers would build such an amplifier if we did go ahead. It might be like some other projects we have done in the past where we have had people seemingly very keen to become involved in an ambitious design, only to lose all enthusiasm when confronted with a complicated kit and a reasonably large outlay of money. For example, it is one thing to say you would like to see a 500W amplifier in the magazine and quite another to go out, buy the kit and build it, when it finally appears in the magazine. So let’s flesh out this high-performance valve amplifier concept. First of all, let’s define high performance, in the valve context. If we do design a valve amplifier, it will need to deliver a total harmonic distortion of around 0.1%; or preferably .01%. That means we will be using negative feedback; in fact we will probably use “nested feedback” and lots of it, with a pushpull output stage. That concept will probably turn off more than half of the valve amplifier aficionados, since they have swallowed the nonsense from some hifi magazines that all feedback is anathema. Secondly, the amplifier will need to be very quiet, in order not to audibly degrade the signals from compact disc and DVD players. We are not likely to be able to achieve the extremely low residual noise of our best SILICON CHIP solid-state designs but we would want to do better than -90dB if possible. Third, we want to go for an output of 50 or 60 watts per channel. Anything less is really not enough with many of today’s relatively low efficiency loudspeakers. And why labour long and hard, and lay out a lot of money, to produce a valve amplifier which produces significantly less output. So that’s the broad concept, with no circuit details, no potential valve list for people to salivate over and nothing else to look forward to other than it would be a “valve” amplifier rather than a “soul-less” solid-state design. That it would be a lot more expensive than a far superior solid-state design delivering lots more power is beyond doubt. How much money? I am guessing but it is likely to be the wrong side of $1000.00. Now the question is: how many readers would go for it? 10? 30? Maybe 100? Without some indication that a reasonable number of people would want to build such an amplifier, the idea just won’t get to first base. If not, well it won’t upset us. Our inclination is to upgrade the popular 15W class-A amplifier which we featured in 1998. So if you really would like to see a 60W/channel valve amplifier (with feedback!), drop us an email. Leo Simpson ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip siliconchip.com.au