This is only a preview of the May 2007 issue of Silicon Chip. You can view 33 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "A 20W Class-A Amplifier Module":
Items relevant to "Adjustable 1.3-22V Regulated Power Supply":
Items relevant to "VU/Peak Meter With LCD Bargraphs":
Items relevant to "Programmable Ignition System For Cars; Pt.3":
Items relevant to "GPS-Based Frequency Reference: Circuit Modifications":
Purchase a printed copy of this issue for $10.00. |
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
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
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
ISSN 1030-2662
* Recommended and maximum price only.
2 Silicon Chip
Publisher’s Letter
New 20W class-A module is
a step closer to perfection
Back in November 2006 we asked the question:
Do people really want a high-performance valve
amplifier? Significantly, we are still getting the
occasional email from people expressing their
interest or otherwise. And while the consensus of
the letters seems to be that people are interested in
valve amplifiers, we are of the strong impression
that comparatively few people would actually
build the then proposed 60W/channel stereo
amplifier with negative feedback.
Interestingly, we expected a number of letters expressing dissatisfaction
with the proposed concept but that was not the case. A number of people
also suggested an updated version of the output transformerless amplifiers
produced by Cyril Murray and other designers in the late 1960s. These were
designed to drive special high-impedance loudspeakers and if we were to
update them, we would actually need to use an output-coupling transformer
to drive conventional low-impedance loudspeakers, so there would not
necessarily be an advantage to that approach.
Regardless of what approach we actually took, our previous experience
leads us to expect that few people would build the final design when they
were confronted with the high price and the amount of the work required
to assemble the amplifier. So we decided to take the alternative approach
and upgrade our very popular 15W class-A amplifier which was featured
back in 1998.
We approached this with some trepidation because we well remember
the problems we had with the power supply and the lengths we had to go
to obtain satisfactory low residual noise. The problems were based on the
heavy fixed current drain from the power supply and the relatively large
hum field produced by the toroidal transformer because of that high current.
However, I am delighted to report that our efforts have borne fruit. As a
result of some very careful analysis of the 1998 design by Peter Smith and
drawing on some circuit techniques advocated by noted audio designer
Douglas Self, we have been able to get some very significant improvements,
as well as a little more power, while keeping overall power dissipation to
levels similar to the old design. This has been achieved by quite a number
of minor improvements to the circuit, a new PC board design and a shielded
toroidal power transformer which has allowed us to eliminate the earlier
design’s regulated power supply which was housed in a separate box.
This month we present the first in a number of articles on the new amplifier module and a subsequent stereo class-A amplifier delivering 20 watts
per channel. Ultimately, it will give far better sound quality than any valve
amplifier and at a far lower price. Nor will its audio performance be degraded
over a relatively short time by component ageing, as happens inevitably in
any valve amplifier.
Leo Simpson
ALTRONICS ADVERTISING CORRECTION
Please note that on page 3 of the advertising flyer included with this issue, several items
in the current “Altronics Price Cuts” promotion are advertised with incorrect prices.
Under “Rack Shelf Discounts”, the part numbers H 5352, H 5362, H 5353 and H 5363
are shown as “2 for”. This is meant to read “2 up” – eg, H 5352 is $45 each when you
buy two or more. Altronics apologises for any inconvenience caused.
siliconchip.com.au
|