Bridge Mode - Peavey PV 2000 Operating Manual

For commercial and other installations where sustained high power operation is required, the amplifiers
should be mounted in a standard 19" rack. It is not necessary to leave a rack space between each
amplifier in the stack since each fan pulls air in from the rear and exhausts the hot air out the front.
However, an adequate 'COOL" air supply must be provided for the amplifier when rack-mounted. The
internal fan must have a source of air that is not preheated by other equipment. The amplifier will start
up in "low speed" fan operation and will normally stay at low speed operation unless sustained high
power operating levels occur. Then, as the amplifier "heat sinks" heat up, the automatic thermal sensing
circuitry will cause high speed operation to occur. Depending upon signal conditions and amp loading,
high speed fan operation may continue or it may cycle continuously between high and low. This
situation is quite normal. If cooling is inadequate due to preheated air, or a reduction of air flow occurs
due to blockage of the amplifier inlet/outlet ports, or if the amplifier is severely overloaded or short
circuited, the amplifier thermal sensing system may cause temporary shutdown of the unit. This is
indicated by the power LED on the front panel ceasing to illuminate. Depending upon the available
cooling air, operation should be restored relatively quickly, and the power LED will be illuminated. In
any event, corrective action should be taken to determine the cause of the thermal shutdown. If the
amplifier is not severely overloaded or shorted and air flow is normal in and out of the amplifier, then
steps should be taken to provide a cooler environment for all the amplifiers. As a general rule, the
cooler electronic equipment is operated, the longer its useful service life.
In most low to medium power applications, the power amplifier can be mounted in any configuration. It
is desirable that, if at all possible, the power amplifier be located at the top of an equipment stack. This
will prevent possible overheating of sensitive equipment by the hot air rising from the power amplifier.
As a general rule, most home and studio requirements will never cause high speed fan operation.
However, if it does, this may indicate that you have not taken the necessary steps to provide adequate
cooling. Remember, closed up in a cabinet, a PV Series power amplifier will have severe cooling
problems, even at low power levels. Again, inadvertent short circuit or sustained overload usage could
also cause temporary thermal shutdown and/or tripping of the mains power breaker. Also, most home
wiring and electrical circuits are only 15 amps. One PV 2000 can cause a 15 AMP breaker to trip if a
severe overload occurs.
The actual operation and usage of the Bridge mode on stereo amplifiers is often misunderstood. In
basic terms, when a two-channel amplifier is operated in the Bridge mode, it is converted into a single
channel unit with a Power Rating equal to the sum of both channels' power ratings at a Load Rating of
twice that of the single channel rating. For example, the PV 2000 is rated at 1000 watts RMS per
channel into 2 ohms. The Bridge Ratings are 2000 watts RMS into 4 ohms (minimum load). Bridge
mode operation is accomplished by placing the mode switch in the "BRIDGE" position, connecting the
positive speaker lead to Channel A red binding post, negative speaker lead to Channel B red binding
post, and using Channel A as the input channel. All Channel B input functions are defeated, and they
serve no purpose now. Another application for Bridge mode operation is to drive sound distribution
systems in very large public address applications. In this mode, any of the PV Series power amplifiers
can actually drive 70 volt systems directly without using matching transformers. The real advantage of
such an approach is primarily cost. 70 volt distribution systems are very common in domestic
applications where large numbers of relatively small loudspeakers are used for background music and
paging. Such systems require the use of 70 volt transformers at each loudspeaker. Another common
use for the Bridge mode is in subwoofer applications where very high power levels are required to
reproduce extreme low frequencies. Such enclosures usually contain 2 or 4 loudspeakers to handle the
power levels involved. For Bridge mode usage, the enclosure impedance must be 4 or 8 ohms-never
below 4 ohms!
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