8
The Nor280 Power Amplifi er
The Nor280 is a rugged, lightweight and
powerful class D amplifier. It is specially
designed for building acoustics applications.
Its output stage is designed to drive almost
any type of load.
The amplifi er comes with a built in noise
generator as standard and as an option it
can be fi tted with a wireless remote control
for switching the signal on/off.
To optimise the power where it is needed a
unique built in equalization network com-
pensates for the falling frequency response of
the speaker system in both the low and high
frequency areas. The equalisation network
also ensures that it is less than 5 dB differ-
ence between two adjacent 1/3 octave bands.
A part of the amplifi ers input stage is a high
pass fi lter that removes low frequency signals
that lie below the required frequency range
for building acoustic measurements and a low
pass fi lter that removes all frequencies above
12kHz. This feature protects the speakers
from distortion and concentrates power into
the frequency bands where it is needed.
The output of the amplifi er is short circuit
protected and an automatic system will guard
against overheating and high signal voltages
through the input. The built in cooling fan is
normally not required but will run at high
room temperatures or during prolonged use
of the amplifi er at full power . It will how-
ever, immediately switch off when the input
signal goes off; this feature makes the unit
well suited to reverberation measurements
in areas of low background noise.
Front panel layout
The front panel consist of a source selector,
a level attenuator, a switch selecting the
equaliser on/off, input and output connectors,
mains connector, mains fuse and switch, an
error indicator and a remote indicator.
Source selector
The Source selector has four positions:
• Line. Selects the input signal connector
and disconnects the internal noise gen-
erator. This allows the use of an external
signal source. Input sensitivity is 1 Vrms
for full power output.
• Pink. Selects pink noise from the internal
noise generator.
• Red/White. Selects Red/White noise from
the internal noise generator.
• White. Selects White noise from the
internal noise generator.
Level selector
The Level selector attenuates the output level
in 5 dB steps from 0 dB (full power) to 35dB.
The fi nal position switches the signal off.
Equalizer switch
The equalizer switch selects the equaliza-
tion network on/off. The switch should be
left in the on position when using Nor250,
Nor270 or Nor270H loudspeakers for maxi-
mum power to the speaker system. It also
ensures that there is less than 5 dB between
each adjacent 1/3 octave band (free fi eld
conditions) when using any of the above
mentioned speakers, as required by annex C
in the ISO140/3 standard.
The equalization network is adapted to the
Nor250, Nor270 and Nor270H loudspeakers.
When using other speakers, it is recom-
mended to switch the equalizer off, or use
the network with care in order not to damage
