Technical information

Macro-Tech 600/1200/2400 Power Amplifiers
Page 18
3.3.6 Additional Load Protection
Macro-Tech amplifiers generate enormous power. If
your loudspeakers do not have built-in protection from
excessive power, it’s a good idea to protect them.
Loudspeakers are subject to thermal damage from
sustained overpowering and mechanical damage from
large transient voltages. Special fuses can be used to
protect your loudspeakers in both cases.
Two different types of fuses are required for thermal
protection 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 contrast, high-speed instrument fuses like the
Littlefuse 361000 series are used to protect loudspeak-
ers from large transient voltages. The nomograph in
Figure 3.15 can be used to select the properly rated
fuse for either type of loudspeaker protection.
Fig. 3.15 Loudspeaker Fuse Nomograph
1.0
1.2
1.4
1.6
2.5
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15
10
8
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2
1.5
1
.8
.6
.5
.4
.3
.2
.15
.1
.08
3000
2000
1500
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1.5
1
LOUDSPEAKER IMPEDANCE
(ohms)
FUSE
(amps)
LOUDSPEAKER RATING
PEAK MUSIC POWER
(watts)
(Typically 4 times the continuous average power)
Answer: Fuse = 1.5 A
2
40
Example:
Impedance = 8 ohms.
Peak Power = 75 W
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
the output of each channel. This makes installation con-
venient because there is only one fuse protecting the
loads on each output. The main disadvantage of this
approach becomes obvious if the fuse blows because
none of the loads will receive any power.
A better approach is to fuse each driver independently.
This allows you to apply the most appropriate protec-
tion for the type of driver being used. In general, low-
frequency drivers (woofers) are most susceptible to
thermal damage and high-frequency drivers (tweeters)
are usually damaged by large transient voltages. This
means that your loudspeakers will tend to have better
protection when the woofers are protected by slow-
blow fuses and high-frequency drivers are protected
by high-speed instrument fuses.
3.4 AC Power Requirements
All Macro-Tech amplifiers are shipped with an appro-
priate line cord. When possible, use a power recep-
tacle on a dedicated circuit and always make sure that
it can supply the correct voltage and curent. We do not
recommend operating your amplifier on voltages
greater than 10% above or below the unit’s rated volt-
age. For example, if your amplifer is rated for 120 VAC,
the line voltage should not exceed 132 VAC. See Sec-
tion 7 for power requirements under a variety of condi-
tions.
All specifications in this manual were measured using
120 VAC, 60 Hz power, unless otherwise noted. Speci-
fications were derived using a voltage that is accurate
to within 0.5% with THD less than 1.0% under all test-
ing conditions. Performance variations can occur at
other AC voltages and frequencies. In addition, line
regulation problems directly affect the output power
from the amplifier.