Additional Load Protection - Crown Macro-Tech 5002VZ Reference Manual

7. If the size of the cable exceeds what you want to use,
(1) find a way to use shorter cables, like using an IQ
System , (2) settle for a lower damping factor, or (3) use
more than one cable for each line. Options 1 and 2 will
require the substitution of new values for cable length
or damping factor in the nomograph. For option 3, esti-
mate the effective wire gauge by subtracting 3 from the
apparent wire gauge every time the number of con-
ductors of equal gauge is doubled. So, if #10 wire is
too large, two #13 wires or four #16 wires can be used
for the same effect.
SOLVING OUTPUT PROBLEMS
Sometimes high-frequency oscillations occur which
can cause your amplifier to prematurely activate its pro-
tection circuitry and result in inefficient operation. The
effects of this problem are similar to the effects of the RF
problem described in Section 3.3.4. To prevent high-
frequency oscillations:
1. Turn on Loudspeaker Offset Integration for each
channel. It includes a low-pass filter to prevent
RF problems (see Section 3.3.4).
2. Lace together the loudspeaker conductors for
each channel (do not lace together the conduc-
tors from different channels). This minimizes the
chance that cables will act like antennas and
transmit or receive high frequencies that can
cause oscillation.
3. Avoid using shielded loudspeaker cable.
4. Avoid long cable runs where the loudspeaker
cables from different amplifiers share a common
cable tray or cable jacket.
5. Never connect the amplifier's input and output
grounds together.
6. Keep loudspeaker cables well separated from
input cables.
7. Install the input wiring according to the instruc-
tions in Section 3.3.4.
Another problem to avoid is the presence of large infra-
sonic currents when primarily inductive loads are
used. Such loads include 70 volt step-up transformers
and electrostatic loudspeakers.
Inductive loads may appear as a short circuit at low
frequencies. This can cause the amplifier to produce
large low-frequency currents and activate its protection
circuitry. Always turn on the LOI circuitry when a prima-
rily inductive load is used. The LOI circuitry provides
protection from most low-frequency input and output
problems.
Page 20
Macro-Tech 5002VZ Power Amplifier

3.3.6 Additional Load Protection

Your amplifier can generate high power levels. If your
loudspeakers do not have built-in protection from ex-
cessive power, it's a good idea to protect them. Loud-
speakers are subject to thermal damage from sustained
overpowering and mechanical damage from large tran-
sient voltages. Special fuses can be used to protect
your loudspeakers in both cases.
Different types of fuses are required for thermal protec-
tion and voltage protection. Slow-blow fuses are usually
selected to protect loudspeakers from thermal damage
because they are similar to loudspeakers in the way
they respond to thermal conditions over time. In con-
trast, high-speed instrument fuses like the Littlefuse
361000 series are used to protect loudspeakers from
large transient voltages. The nomograph in Figure 3.13
can be used to select the properly rated fuse for either
type of loudspeaker protection.
There are basically two approaches that can be taken
when installing fuses for loudspeaker protection. A
common approach is to put a single fuse in series with
1.0
1.2
1.4
1.6
2
2.5
3
4
5
Example:
6
Impedance = 8 ohms.
Peak Power = 200 W
7
8
Answer:
Fuse = 2 A
9
10
12
14
16
20
25
30
40
Fig. 3.13 Loudspeaker Fuse Nomograph
20
3000
15
2000
10
1500
8
1000
800
6
600
5
400
4
300
3
200
150
2
100
80
1.5
60
1
40
.8
30
.6
20
.5
15
.4
10
8
.3
6
4
.2
3
.15
2
1.5
.1
1
.08
Reference Manual