SILICON CHIP
Publisher & Editor-in-Chief
Leo Simpson, B.Bus.
Editor
Greg Swain, B.Sc.(Hons.)
Technical Staff
John Clarke, B.E.(Elec.)
Robert Flynn
PUBUSHER'S u:·1-1'ER
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Paul Buchtmann
Regular Contributors
Neville Williams, FIREE, VK2XV
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Jim Yalden, VK2YGY
Garry Cratt, VK2YBX
Jim Lawler, MTETIA
David Whitby
Photography
Bob Donaldson
Editorial Advisory Panel
Philip Watson, MIREE, VK2ZPW
Norman Marks
Steve Payor, B.Sc., B.E
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2
SILICON CHIP
Decision trees
and preamplifiers
It is quite surprising how, when a particular project has been
designed for the magazine, a whole host of related applications then
suggest themselves. Sometimes we can act immediately on these ideas;
at other times they remain to be followed up later.
The most recent example of this was when we designed the
50/lO0W module published in December 1987. No sooner had we
published it than the idea of a higher-rated stereo power amplifier
was mooted. The result was the Studio 200 power amplifier described
in February 1988. And as soon as that hit the streets, we had readers
clamouring for a matching stereo control preamplifier and other
related projects.
Luckily, we had foreseen the demand for a stereo control unit and
started development work on it as soon as possible. The result appears
in this issue, as part one of a two-part article.
We're very proud of the Studio 200 Control Unit. Whether it will be
hailed by the dyed-in-the-wool hifi enthusiast we don't know but it does
bring together a number of highly desirable features.
First of all, it uses a new low-noise dual op amp, the LM833, from
National Semiconductor. This op amp not only has very low noise, but
is also very cheap.
Second, by using these LM833 op amps, we have been able to keep
the circuit complexity to a pleasingly low level; just four dual op amps,
four transistors and four diodes, plus the power supply components.
As a result, the overall price of the control unit should be something of
a benchmark for economy; a little over $200.
Third, the overall performance is as good as or better then virtually
any stereo preamp/power amp combination costing up to $3000 or
more. By contrast, the overall cost of the Studio 200 preamp/power
amp combo is going to be around $630.
Just to focus on one aspect of performance, the unweighted signal to
noise ratio for the high level inputs is 103dB or better. Very few
amplifiers, regardless of price, offer this level of performance. That
may seem surprising, but it's the kind of performance needed if the
amplifier chain is not to degrade the signal quality from compact
discs.
Finally, the new control unit has an excellent headphone output
with exactly the same level of performance. This is unusual for two
reasons. Most stereo control units do not have headphone outputs at
all and most integrated amplifiers give mediocre performance from
their headphone sockets.
This is the third in a series spawned by the original project published back in December 1987. We have quite a few to go before the series
will be exhausted. When you consider all the projects we have
published so far and all the possible project ideas that will flow from
each of these, that's a lot of decision trees. How many projects will it
mean over the next few years?
Leo Simpson
