What is the efficiency advantage of the DA-70
Series over other amplifier designs?
As shown in the figure below, the ternary design has a 20%
advantage over binary Class D at music levels (typically 15%
of full scale) and about 3 times the efficiency of analog
amplifiers!
The Power Supply
The foundation of all amplifier design is the power supply. For
years Stewart Audio has pioneered leading edge, power sup-
ply technology. All Stewart Audio amplifiers feature a High-
Frequency Switch Mode Power Supply. Because of this use of
advanced technology some explanation is in order.
Conventional Power Supplies operating at 60Hz (standard line
frequency) recharge only 120 times per second, requiring
their storage capacitors and transformers to be quite large to
supply the energy needed during the intervals between cycles
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B+=12vdc, 1kHz, Rload=4 ohm.
If mounted in a sealed rack, leave the top and bottom spaces
open to create a chimney effect within the rack, which will
provide cooling as air is drawn in the bottom and exhausted
out the top. The amount of airflow necessary will be deter-
mined by a number of factors, including ambient tempera-
ture, the amount of heat generated by other equipment in
the rack, the properties of the enclosure being used, and how
hard the amplifier is working. In extreme cases it might be
necessary to install a cooling fan in the rack for additional
cooling.
In free standing installations where the amplifier is sitting on
a shelf or hard floor the four rubber feet must remain
mounted to the bottom of the amplifier. Under no circum-
stances should the amplifier be placed directly on carpeting
or similar surfaces.
AC Power Considerations
Your Stewart Audio DA-70-2 and DA-70-4 amplifiers are de-
signed to operate on 120 volt, 60 Hz AC current.
Your Stewart Audio DA-70-2-PFC and DA-70-4-PFC amplifi-
ers are designed to operate over a range of 90 volts - 240
volts, 50-60 Hz alternating current.
Average power consumption will depend on load impedance,
signal level and program material.
Typical power consumption in Amperes:
(All channels driven @ 4 Ohms /120V AC)
Model Idle 1/8 power 1/3 Power Full Power
DA-70-2 .2 .4 .6 1.4
DA-70-4 .3 .7 1.3 3.0
DA-70-2-PFC .2 .4 .7 1.6
DA-70-4-PFC .3 .8 1.4 3.2
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