high-power operating levels occur. Then, as temperatures in the amplifier heat sinks increase, 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 the fan may cycle continuously between high and low. This situation is quite normal. If cooling is inadequate, however, the amplifier thermal-sensing system may cause temporary shut down of the unit, indicated by the PWR LEDs on both channels going dark. Inadequate cooling may be due to preheated air, reduced air flow resulting from blockage of inlet/outlet ports, severe amplifier overload, or short circuit conditions. Depending upon the available cooling air, operation should be restored relatively quickly, and the power LEDs on both channels will again be illuminated. In any event, action should be taken to correct 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 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. High-speed operation may indicate that you have not taken the necessary steps to provide adequate cooling. Fully closed up in a cabinet, a PV® Series power amplifier will have severe cooling problems, even at low power levels.
BRIDGE MODE
The Bridge mode on stereo amplifiers is often misunderstood relating to actual operation and usage. In basic terms, when a 2-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 the power rating for each channel, at a load of twice that of the single-channel rating. For example, the PV 1500 is rated at 750 Watts RMS per channel into 2 Ohms. The Bridge rating is 1500 Watts RMS into 4 Ohms (minimum load). Bridge mode operation is accomplished by placing the MODE switch in the BRIDGE position, using only the BRIDGE Speakon® connector or the red binding posts for the output, and using the CHANNEL A input. All CHANNEL B input functions are defeated and serve no purpose now. Bridge mode operation can be used to drive sound distribution systems in very large public address applications. Another common use for the Bridge mode is in subwoofer applications where very high power levels are required to reproduce extremely low frequencies with adequate headroom. 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.
DDT™
Peavey’s patented DDT (Distortion Detection Technique) compression circuit enables the sound technician to maximize the performance of the amplifier/speaker combination by preventing the power amplifier from running out of headroom (clipping). This compression system is activated by a unique circuit that senses signal conditions that might overload the amplifier and activates compression (reduces the channel gain) when clipping is imminent. The threshold of compression is clipping itself, and no specific threshold control is used. This technique effectively utilizes every precious watt available for the power amplifier to reproduce the signal, while at the same time minimizing clipping and distortion. DDT significantly reduces the potential of loudspeaker degradation and damage, and is the most effective, automatic, hands-off approach to the problem of power amplifier clipping.
Since PV series power amplifiers use a circuit breaker for overcurrent protection, the DDT compression system plays an even more important role in continuous performance by preventing each channel from clipping and overload. Continuous operation at clipping can cause the circuit breaker to trip, but with the DDT activated, this problem is minimized. For this reason, the DDT compression system should always be enabled.
