User Guide

Page 10

dm38

Output current limiting

In terms of maximum available output current, there are basically 3 amplifier type

options:

a. An amplifier with a reasonable limit placed on the maximum available output

current.

b. 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.

c. 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 (amplifier type a. or c. 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 type b. or c. 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

150W 49V 4.33A 6.12A

4 ohms

300W 49V 8.66A 12.25A

2 ohms

600W 49V 17.32A 24.5A

1 ohm

1200W 49V 34.64A 49.A

If the loudspeaker cable is inadvertently shorted out, these sorts of currents are quite

capable of causing some cables to catch fire. We know of one such instance with an

amplifier rated according to the table!

As we do not wish to set your house on fire we have limited the peak output current

to 15A.