16
Output Current Limiting
In terms of maximum available output current,
there are basically three amplifier type options:
•
an amplifier with a reasonable limit placed
on the maximum available output current
•
an amplifier with no limit placed on the
maximum available output current, which
will either blow a fuse or self destruct if
excessive current is drawn, for example
through a dead short
•
an amplifier with a very high limit placed
on the maximum available output current,
but designed not to blow a fuse if this
very high current is drawn
If the maximum current drawn from an
amplifier with maximum available current
limiting is reached under very loud music
conditions (the first and third amplifier
types above), highly obvious “cracking”
overload sounds may be heard. Note that this
overload sound may also occur if a
loudspeaker overloads or if any amplifier
suffers voltage overload.
There is an expectation in the audiophile
electronic industry that a high end amplifier
should be capable of delivering exactly double
the output current for a halving of the
loudspeaker impedance (down to 1 ohm) at
the maximum output voltage that the amplifier
can produce.
This requires an amplifier of the second and
third type above. The table below lists an
example of an amplifier rated at 150 watts
output into 8 ohms.
Loudspeaker
load impedance
Output power
Peak output
voltage
r.m.s. output
current
Peak output
current
8 ohms
150 W
49 V
4.33 A
6.12 A
4 ohms
300 W
49 V
8.66 A
12.25 A
2 ohms
600 W
49 V
17.32 A
24.5 A
1 ohm
1200 W
49 V
34.64 A
49.0 A
