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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
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
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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.
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