This is only a preview of the January 1998 issue of Silicon Chip. You can view 32 of the 88 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 "Build Your Own 4-Channel Lightshow; Pt.1":
Items relevant to "Command Control For Model Railways; Pt.1":
Items relevant to "Build A One Or Two-Lamp Flasher":
Articles in this series:
Articles in this series:
Purchase a printed copy of this issue for $10.00. |
• You can reduce the power of this
module by removing a pair of output
transistors as you suggest and then
reducing the supply rails to about
±34V. However, we are inclined to
think that using this module to deliver
only 50W is a bit of a waste. Have you
considered the 50W LM3876 module
described in the March 1994 issue? It
is cheaper and has short circuit protection. You would be advised to add
the reverse biased diodes between the
output and the supply rails, as in the
175W module.
Amateur band receiver
needs alignment
I have made up a 3-band amateur
receiver (SILICON CHIP, September
1996) and I am having problems. As
supplied, my kit is slightly different
from the published design. While the
circuit specifies a number of 150pF
capacitors, the PC board component
layout has 68pF capacitors. Also for
the F14 balun (T1), the copper wire
supplied was not right because I could
not get the right turns and had to go to
a smaller gauge. Now, when I tune VR2
across the bands I only get one amateur
station and one shortwave station all
over the bands. Can you please tell
me where I am going wrong? (W. S.,
Christchurch, NZ).
• We note that the PC board in your
kit has changed capacitors compared
with our article but unless you are
unable to set the trimmer capacitors to
give the precise oscillator frequencies,
these changes are not important.
You do not say whether you have
been able to correctly align the receiver as outlined in the article. You will
also need a fairly good antenna if you
are to receive a reasonable number of
stations. Have you put up an antenna,
as suggested in our article?
Is rectifier buzz
a problem?
I am preparing to build a compact, high performance amplifier
for studio headphones, which I
intend to use as the “heart” of a
no-compromise listening system to
be packed into a suitcase. It is to be
housed in a small metal enclosure
and powered from a 16V 1A AC
plugpack.
This arrangement appeals to me
most of all possibilities and I can
derive the two different split-rails
that are required for the device’s
operation “internally”, including
rectification, filtering, stabilisation,
decoupling, etc.
It means, however, that the transformer will be connected to the
rest of the power supply circuitry
by about 2m of cable. Conventional wisdom implies a danger of
“rectifier noise” radiation which
could affect the performance of the
device, as well as other electronics
in the vicinity.
How serious is this danger, for
the given voltage and current? What
kind of filter could I use and where,
to safeguard against this? Would
some sort of shielding on the plug
pack lead be worth considering?
And finally, would you suggest
a larger case containing a transformer to be a better option – from
the noise viewpoint alone? The
amplifier will have an active tone
control stage which I believe is
especially prone to hum pickup.
(A. K., Douglas, Qld.
• Conventional wisdom is right as
far as rectifier noise is concerned. It
is almost impossible to adequately
suppress rectifier noise radiated by
a cable and it is even more difficult
if the device you are using does not
earth the core of the transformer.
Having said that, the only way
to gauge the serious
ness of the
problem is to give your proposed
arrangement a try. It may be quite
satisfactory. If not, you will need
to resort to a more conventional
power supply arrangement.
Notes & Errata
Stepper Motor Driver With Onboard
Buffer, December 1997: the overlay
diagram on page 64 shows a .01µF
capacitor connected to pins 1 and 4 of
IC2. This should be a .001µF as shown
in the circuit and parts list.
240VAC 10A Motor Speed Controller,
November 1997: while this controller is suitable for power tools with
nameplate ratings up to 10A, it is
not suitable for appliances such as
2400W radiators which draw 10A
continuously.
We have also been advised that the
mica washers supplied in some early
kits have been prone to flashover to
the case. To avoid this, we suggest that
a minimum of two mica washers be
used for both the fast recovery diode
and the IGBT.
Better still, we suggest that SIL-PAD
heatsink washers, a composite of silicone rubber and fibreglass be used,
as these have a considerably higher
voltage rating. The SIL-PAD 400 (.007)
has a breakdown rating of 3.5kV AC.
WARNING!
SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects
should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out
according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally
come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains
voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability
for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine.
Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement
of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which
are used in such a way as to infringe relevant government regulations and by-laws.
Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices
Act 1974 or as subsequently amended and to any governmental regulations which are applicable.
January 1998 85
|