Meyer Sound 650-P - Manual (Page 6)

6
When the safe continuous power level is exceeded, a
single limiter engages, affecting both amplifier channels
equally. TPL activity is indicated by the Sub Limit LED
on the user panel. The limiter ceases operation when the
power level returns to normal and does not affect the
signal when the LED is inactive.
The 650-P performs within its acoustical specifications
and operates at a normal temperature if the TPL LED is
on for no longer than two seconds, and off for at least
one second. If the LED remains on for longer than three
seconds, the 650-P is hard limiting with these negative
consequences:
• Increasing the input level will not increase the
volume.
• The system distorts due to clipping and nonlin-
ear driver operation.
• The life-span of driver and amplifier components is
reduced because they are subjected to excessive
heat.
The TPL LED can indicate an imbalance in a system of
speakers by functioning like a spectrum analyzer. If
speakers in a subwoofer, mid-bass, or mid-hi subsystem
begin to limit before reaching the required operating
level for the entire system, then that subsystem needs to
be supplemented with additional speakers.
NOTE: Although the TPL limiters exhibit smooth sonic
characteristics, we do not recommend using them for
intentional compression effects. Use an outboard
compressor/limiter to compress a mixed signal.
Driver Excursion Clamp
The drivers in the 650-P are protected from over-excursion
by an excursion clamping circuit that does not have
attack or release time constants. The circuit provides
instantaneous braking for the drivers without the
pumping effects commonly produced by compressor/
limiters.
The circuit uses sophisticated filters to minimize the
distortion normally caused by clamping and clipping.
As the 650-P’s input signal is increased past the clamping
point, the output signal remains at a fixed level, protecting
the drivers and minimizing negative sonic effects. The
650-P operates safely if the Exc. Clamp LED is on for no
longer than two seconds, and off for at least one second.
Fans and Cooling System
The 650-P uses a forced-air cooling system with two
fans to prevent the amplifiers from overheating. The
fans draw air in through ducts on the front of the
cabinet, over the heatsinks, and out the rear of the
cabinet. Since dust does not accumulate in the amplifier
circuitry, its life-span is increased significantly.
A foam insert filter, in combination with the entire front
grill surface, acts as an air filter for the cooling system.
Despite the filtering, extensive use or a dusty operating
environment can allow dust to accumulate along the
path of the airflow, preventing normal cooling. We
recommend periodically removing the grill, filter, and
amplifier module and using compressed air to clear
dust from the grill, filter, fans, and heatsinks. Make sure
that the air ducts are clear and that there is at least six
inches clearance for exhaust behind the cabinet.
air
intake
cooling
fans
heatsinks
air filter
power
supply
A variable-speed primary fan runs continuously with
an inaudible operating noise of 22 dBA at 1 m at its
slowest speed. The speed of the primary fan begins
increasing when the temperature of the heatsinks reaches
42°C. The fan reaches full speed at 62°C and is barely
audible near the cabinet, even without an audio signal.
In the unusual event that the heatsink temperature
reaches 74°C, the secondary fan turns on; it turns off
when the temperature decreases to 68°C. The second-
ary fan is audible at close proximity without an audio
signal and turns on in response to
• primary fan failure (check its status immediately);
• a prolonged period of high source levels in hot
temperatures or direct sunlight;
• accumulation of dust in the cooling system path;
• driver failure.
TROUBLESHOOTING NOTE: In the highly unlikely event
that the secondary fan does not keep the temperature
below 85°C, the 650-P automatically shuts down until AC
power is removed and reapplied. If the 650-P shuts down
again after cooling and reapplying AC power, contact
Meyer Sound for repair information.