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Running a 120V
cassette recorder
I have recently obtained a Sony
25W CD/radio cassette-corder from
the US. My only problem is that it
needs a 120VAC 7A power supply.
I do though have a 115VAC 0.53A
transformer that I can plug the
Sony straight into but as you have
already guessed, it is no substitute
as the tape deck will run at a slower
speed.
I would like to know if there is a
transformer that I can use in place
of my existing one or can I pump up
the current rating on it by building
a circuit for it (if there is such a
thing)? (C. R., Winston Hills, NSW).
• It should be possible to power
your Sony CD/cassette player from
your 115VAC transformer without
problems, in spite of the fact that
our AC mains system is 50Hz
instead of 60Hz. These days we
would expect that most cassette
decks would be run from an internal DC supply and thus are not
locked to the frequency of the AC
mains supply. Give it a try; you are
unlikely to do any damage.
On the other hand, if the cassette
transport mechanism is lock
ed
to the mains frequency, then you
could drive it with an inverter
which delivers 60Hz. Unfortunately, we have not designed a
project to deliver 110VAC at 60Hz
although we did publish a 12V
DC to 240VAC 40W inverter in
February 1992. This was able to be
modified to deliver 60Hz.
K
ALEX
The UV People
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to the ignition side of the circuit
and, depending on the engine speed,
vary the amount of advance. In your
opinion would a kit of this nature be
relatively easy to design and build?
(S. B., Casino, NSW).
• Such a project would really only
be feasible if it contained a microprocessor which would have to be
programmed with the characteristics
you require. While it is feasible, we do
not think we could justify the development cost in view of the relatively
small number of readers who would
want to make this radical modification
to their cars.
Power amplifier
failure
For the past five years I have been
using the Studio 200 preamplifier
and power amplifier combination
without any problems whatsoever.
Recently, however, I combined the
two with an active crossover network
and proceeded to destroy the power
transistors in both channels of the
amplifier.
Failure of these components was not
instantaneous. There was a gradual
degradation in the performance of the
system over about a week before the
amplifier failed completely, blowing
the speaker protection fuses. During
this period, I reversed the outputs from
the crossover into the power amp on
several occa
sions while attempting
to diagnose the problem. This may be
the reason for both channels failing.
I would appreciate any help you
may be able to provide regarding
possible reasons for my problem. (P.
K., Picnic Point, NSW).
• While we cannot be sure, it seems
likely that the electronic crossover
is the cause of the problem since the
combination of the power amplifier
and preamplifier had been reliable.
In our experience, this preamp/power
amplifier combination is very reliable
and so we suggest that you have the
electronic crossover checked for high
frequency instability.
If the electronic crossover is oscillating at a supersonic frequency it could
cause the power amplifier stages to
become very hot and ultimately, to
fail. The clue in this is that you said
the performance was degraded. Often,
one of the symptoms of supersonic
oscillation is that the sound does not
seem quite right. We suggest you make
sure that the electronic crossover is
completely fault-free before using it
with any system again.
Notes & Errata
Coolant Level Alarm, June 1994: the
circuit on page 21 has an error in that
the indicator lamp is connected to the
decoupled +12V supply line; ie, after
D2. It should go to the +12V line from
the ignition switch, as shown correctly
on the wiring diagram on page 22.
K
ALEX
40 Wallis Ave, East Ivanhoe 3079.
Phone (03) 9497 3422, Fax (03) 9499 2381
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Phone (02) 642 6003 Fax (02) 642 6127
February 1995 93
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