Requiring far less capacitance for filtering and storage. This high-speed
recharging reduces power supply “sagging” common with other designs. In a
Stewart Amplifier, it is almost as though power is fed directly from the wall to
the speaker with the amplifier acting only as a “valve” in-between to control
its flow. The power supply’s remarkable efficiency at converting energy from
the Ac line to a usable form for loudspeaker applications allows many of the
major components to be downsized , saving space, weight and cost.
Absolute Protection
Stewart Audio power amplifiers employ circuits which fully protect
the amplifier while avoiding sonic compromise. For example, a unique
circuit monitors the current drawn from the power supply. The
amplifier’s output is not affected in any way until the power rating is
exceeded, indicating the presence of a short or overload. Under these
conditions the power supply will simply shut down until the short is
removed, at which point the supply will slowly ramp up to full power,
protecting the load from a surge of energy. In the event of an
amplifier malfunction this circuitry will also protect the speakers,
since the power is immediately disconnected from the amplifier.
Most other amplifier designs require the presence of relatively high
levels of signal in order to detect a shorted output. At low signal
levels, such amplifiers will continue to drive a short, causing rapid
heat buildup, thermal runaway, and finally amplifier failure. The
current-sensing circuitry in all Stewart Contractor Series amplifiers is
capable of detecting a shorted output even at low program levels,
increasing reliability under conditions which could cause other
amplifiers to fail.
7
Installation
Mechanical Consideration
The Stewart Audio CVA-7400/CVA-7800 occupies one standard rack space
and is only 15” deep and weighs just 10 and 11 pounds respectively,
making it easier to install and transport than almost any other comparable
amplifier. Still, some sensible precautions are in order.
Always use four screws to affix the amplifier to the rack, preferably using
flat washers as well to avoid cosmetic damage to the front panel. When rack
mounting your amplifier it may be necessary to remove the four rubber feet
from the bottom of the unit (in freestanding installations the rubber feet
must be installed). In mobile rack-mounted installations it is recommended
that the rear of the amplifier be stabilized for additional support.
Thermal Considerations
Cooling of the CVA-7400/CVA-7800 is achieved convection, through
heatsinks mounted on each side of the amplifier. In the event that the
chassis temperature reaches 87 degrees C an internal thermostat will open,
turning off the power supply until the amplifier cools down. Although the
CVA-7400/CVA-7800 sophisticated thermal management system makes it
less susceptible to overheating than other amplifiers, it remains necessary to
provide airspace around the chassis. This may mean leaving a rack-space
open above the amplifier. Multiple amplifiers can be racked on top of one
another by leaving a full space between them so sufficient airflow is main-
tained to allow heat to escape. If mounted in a sealed rack, leave top and
bottom spaces open as well to create a “chimney” effect within the rack,
which will provide cooling as air is drawn in the bottom
10
