Page 13
CP660
Six Channel Amplifier
Reference Manual
There are mainly two different approaches used when
installing fuses for loudspeaker protection. A common
practice is to put a single fuse in series with the output
of each channel. This makes installation easy because
there is only one fuse per channel to install, but it can
also lead to problems. The biggest disadvantage be-
comes apparent if the fuse blows because power to all
connected loads will be removed.
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.
Fig. 3.5 Loudspeaker Fuse Nomograph
1.0
1.2
1.4
1.6
2.5
3
4
5
6
7
8
9
10
12
14
16
20
25
30
20
15
10
8
6
5
4
3
2
1.5
1
.8
.6
.5
.4
.3
.2
.15
.1
.08
3000
2000
1500
1000
800
600
400
300
200
150
100
80
60
40
30
20
15
10
8
6
4
3
2
1.5
1
SPEAKER Z
(ohms)
FUSE
(amps)
SPEAKER RATING
PEAK MUSIC POWER
(watts)
(Typically 4 times the continuous average power)
Example: Z = 8 ohms.
Peak Power = 75 W
Answer: Fuse = 1.5 A
2
40
Two different types of fuses are required for thermal pro-
tection and voltage protection. Slow-blow fuses are usu-
ally 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
Littelfuse 361100 series are used to protect loudspeak-
ers from large transient voltages. The nomograph in Fig.
3.5 can be used to select the properly rated fuse for
either type of loudspeaker protection.