Amplifier load tolerance
An efficient loudspeaker in live concert conditions can act as a surprisingly dynamic
and complex load. Most modern touring power amplifiers claim 2 Ohm capabilities
but make sure your amplifier is also capable of driving reactive (ie inductive or
capacitive) loads without prematurely clipping or developing output stage crossover
distortion.
Power Reserve
Most power amplifier specifications are based on bench measurements made using
stable, high current mains supplies and well defined loads.
Amplifiers sound best when they have plenty of current in reserve for musical peaks.
General power amplifier reminders
1) Try to ensure that the mains supply stays within the amplifier manufacturer’s
specified range from no load to maximum load. An electrical technician
should check the mains supply vs demand using an accurate true rms voltage
meter.
2) If unfamiliar generators are being used the electrical technician should check
the mains waveform (using a portable ’scope-meter) to make sure that it is
sinusoidal and not crawling with spikes or interference.
3) Avoid driving more than one W8CT high-mid or high section or one W8CM
cabinet per power amplifier channel. This will keep the power amplifier’s 2
ohm capability in reserve for musical peaks.
4) Avoid using power amplifiers in bridged mode. Most commercial power
amplifiers are optimised for 2-channel operation. It is usually better to use the
appropriate amplifier in 2-channel mode than to use an inadequate amplifier
in bridged mode.
Gain or level settings
Gain switches
If you are lucky enough to have amplifiers with user gain switches, set them all to
identical positions. A voltage gain in the range 23-33dB will provide a good balance
of system headroom and noise (assuming professional audio equipment is in use
FOH).
Level controls
The front panel level controls should be turned down (fully counter clockwise) until
FOH-to-Amp rack lines have been checked and controllers have been set to suit the
power amplifiers to be used (see Section 2.5). Music should be used to check that
controllers are receiving and sending the appropriate signal bands and then each
All material © 2007. Martin Audio Ltd. Subject to change without notice.
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