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occur. If the internal temperature rises, the transistors may be damaged. Take care not to block the ventilation
holes.
6. USE OF CHEMICAL CLEANING
CLOTH
|
When
cleaning the cabinet, avoid using a chemical cleaning cloth as it may discolor the cabinet surface or peel
off the coating.
Operation Precautions for the
Dynaharmony Amplifier
This model
incorporates
a Dynaharmony
ampli-
fier which
means that peak power outputs more
than
twice
as
high as the
rated
power
output
are reproduced without distortion. As a result, the
sound
is clear even under high-power output con-
ditions and so, compared with normal amplifiers,
the power
level can be increased when
listening.
However, when the amplifier operates continuous-
ly for a prolonged period of time at a power out-
put which is higher than the rating (75 watts), it
functions in the same way as a Class B amplifier,
and the protection circuit Is sometimes actuated
due to overdrive. A good idea is to use the ampli-
fier with the peak indications of the meters at a
level lower than the peak value at which the ampli-
fier is capable of sound
reproduction
(150 watts
with the SR-904).
The superiority and the principle of operation of
the Dynaharmony amplifier are now outlined.
(1) Until the debut of the Dynaharmony
amplifier
The
level
of a music
source
Is constantly
undergoing
variations.
The number of varia-
tions, however, is greatly reduced with a high-
level signal input (for instance, less than -6 dB
of the peak value), and they are less than 2%
of the total time.
Nevertheless,
in order to
reproduce
high-level
signals without
distor-
tion, the conventional
method
was to drive
the
transistors
with
a
high
voltage.
This
increased
the size of the power transformer
and heat sinks, raised the power consumption
and downgraded the efficiency. With a view to
improving
these points,
Hi TACHI
developed
the Dynaharmony
amplifier which is really a
combination
of a high-power output and a
low-power
output
amplifier.
The
amplifier
is selected in accordance with the input signal
level. This model also contains a Dynaharmony
amplifier,
and this
provides
for
improved
efficiency and also for a peak power output
oer channel of 150 watts.
(2) Principle of operation
As illustrated
in the above figure, the power
supply
is divided
into a high-voltage
power
High power amplifier
High voltage
power supply
Low voltage
LOAD
Low power
amplifier
supply (+B2} and a low-voltage power supply
(+B1). The power transistors are also divided
into two sets: one for high-power output and
the other for low-power output applications.
(With
the
conventional
Class
B amplifier,
there was only one set of transistors serving
for both high and low-power outputs.) When
the input level of the signals is low, only the
low-power Output amplifier operates with the
low-power
Output
transistors
and
the
low-
voltage
power
supply
(+B1)
supplies
the
current.
When, however, the input level of the signals
reaches a certain value, both sets of transistors
are actuated, This acts as the high-power out-
put amplifier, and the current is supplied from
the high-voltage power supply (+B2). In other
words,
under
normal
input
conditions, the
low-power
output
amplifier
alone operates,
and the power consumption is kept down to a
low level (since current flows from the low-
voltage power supply only). All this means is
that
the power
supply
for the
high-power
output amplifier is increased
more than that
of conventional
amplifiers with a low power
consumption,
and
that
high
peak
power
Outputs
are
reproduced
without
distortion.
power supply
—
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