Crown ma-5000vz 参照ガイド

recorders. The LOI circuitry will also help to avoid this
potential problem. It includes a second-order Bessel
low-pass filter with a –3 dB frequency of 50 kHz.

A third problem to avoid is hum. The two most com-
mon sources of hum in an audio system are inductive
coupling and ground loops.

Inductive coupling can occur when input cables are
subjected to a magnetic field from a power cord or
power transformer. One way to prevent inductive cou-
pling is to lace the input cables together along their
length and route them as far away as possible from
power transformers and power cords. The use of
shielded pair cable is another effective way to reduce
or eliminate hum resulting from inductive coupling.

Ground loops often result when two or more devices
are improperly grounded. This causes undesirable
stray currents that may produce hum in the output. The
best way to avoid ground loops is to ensure that all
system devices are plugged into the same power strip.
In addition, make sure that all cable shields are
grounded at one end only.

Input and output grounds are sometimes tied together
for testing or metering. This can cause feedback os-
cillation from load current in the test loop. In some sys-
tems, even the AC power line may provide this
feedback path. To avoid this problem, use proper
grounding, isolate the inputs and other common AC
devices. If needed, the input signal ground can be iso-
lated from the AC mains ground with the ground lift
switch located on the PIP2–FXQ (see Figure 3.11 and
Section 4.4).

SOLVING INPUT PROBLEMS

Sometimes large infrasonic (subaudible) frequencies
are present in the input signal. This can cause output
clipping and off-center woofer cone movement. As a
result, the loudspeakers may handle less power and
could be damaged by overload or excess heat. To re-
duce the risk of such problems, turn on the Loud-
speaker Offset Integration (LOI) for each channel. The
LOI switches are located on the back panel of the am-
plifier. This circuitry includes a third-order high-pass
Butterworth filter with a –3 dB frequency of 35 Hz.

Fig. 3.10  Loudspeaker Offset Integration Switch

Another problem to avoid is the presence of large lev-
els of radio frequencies (RF) in the input signal. Al-
though high RF levels may not pose a threat to the
amplifier, they can burn out tweeters or other loads that
are sensitive to high frequencies. Extremely high RF
levels can also cause the amplifier to prematurely acti-
vate its protection circuitry, resulting in inefficient op-
eration. RF can be introduced into the signal by local
radio stations and from the bias signal of many tape

1. Use only shielded cable. Cables with
higher density shields are better. Spiral
wrapped shield is not recommended.

2. When using unbalanced lines, keep the
cables as short as possible. Avoid cable
lengths greater than 10 feet (3 meters).

3. Do not run signal cables together with
high-level wiring such as loudspeaker wires
or AC cords. This reduces the chance of hum
or noise being induced into the input cables.

4. The amplifier should be off for at least
10 seconds  before changing any connec-
tions. This amplifier can produce lethal output
energy and can drive loudspeakers to levels
that can cause permanent hearing damage.
Turn down level controls completely before
powering the system back up. Crown is not
liable for personal injury or damage that can
result when a system component is
overdriven.

3.3.5 Output Connection
Consider the power-handling capacity of your load be-
fore connecting it to the amplifier. Crown is not liable for
damage incurred at any time due to overpowering.
Fusing loudspeaker lines is highly recommended (see
Section 3.3.6). Also, please pay close attention to the
precautions provided in Section 4.1.

Fig. 3.11  Input Ground Lift Switch