4. Operation
IMPORTANT
All signal source equipment should be adequately
earthed. This not only ensures your safety but
everybody else's as well. Faults can and do occur in
mains connected equipment where the chassis can
become “live” if it is not properly earthed. In these
instances the fault in a “floating” (un-grounded) piece of
equipment will look for the shortest path to ground
which could possibly be your amplifier's input. If the
fault current is large enough it will destroy the input to
your amplifier and look for the next available path,
which may be you!
Before making any connections to your amplifier
observe the following:
Ensure the mains voltage supply matches the label
on the rear panel of your amplifier (+/- 10%).
Ensure that the power switch is OFF (UP)
Ensure that all system grounds (earths) are
connected from a common point. Avoid powering
equipment within a system from multiple power
sources that may be separated by large distances.
Check the continuity of all interconnecting leads to
your amplifier, ensure that there are no open or
short circuited conductors.
Ensure that the power handling of your load
(speakers) can adequately cope with the power
output of the amplifier.
Very Important
Due to the high power ability of the
AM1200
you need
to be aware that certain precautions need to be
followed to ensure longevity of your amplifier:
- Never
turn your amplifier on unless all connections
(inputs and speakers) have been made!
- Never
plug in a signal lead after the amplifier has
been turned on! Turn the unit off first.
- Never
drive the output into clipping if the load is
open circuit or there is no speaker load connected!
Powering Up
REMEMBER
The amplifier should be the last piece of equipment that
you turn on and the first piece of equipment that you
turn off.
We recommend turning the attenuators on your
amplifier down when turning the unit on.
When you power up your amplifier, your amplifier
goes through an establishment period before it will
accept signal. The Inrush Current Suppression (ICS)
circuit is in operation for the first 0.5 seconds. This
limits the mains current to prevent "nuisance tripping"
of circuit breakers.
During this period the THERMAL LED will flash red
whilst the mains voltage gradually charges up the
power supply. You will then hear a relay “click”,
indicating mains is now directly applied to the amplifier.
While the ICS circuit operates there is also a 30dB
mute on the signal input. After two seconds this mute
will release, allowing any applied signal to pass
unattenuated.
When switching the amplifier off, wait a couple of
seconds before switching the unit on again. This allows
the ICS circuit to reset.
Level Matching
The normal operating position for the attenuator is
the "0 dB" position (fully clockwise, no attenuation).
In this position the amplifier operates at full gain.
Turning the attenuator back (anticlockwise) reduces
the input sensitivity by the amount marked on the
attenuator scale (dial).
NOTE: If full power output is required you should
operate your amplifier with the front panel attenuator
above the -15dB position, otherwise clipping of the
input circuitry and its resultant distortion will occur
before full output power is achieved.
Sensitivity
Your amplifier is a linear device operating with a fixed
input to output voltage gain (less attenuation). The
maximum output voltage swing is determined by the
applied mains voltage, load, load type and the duty
cycle of the applied signal.
The voltage gain factor of your amplifier is: 37 times or
31.4dB.
The input sensitivity for your amplifier when the
attenuator is at the “0” dB attenuation position (fully
clockwise) is nominally:
+3.0dBu (1.10volts in) for rated power into a 8 ohm
load.
+1.6dBu (0.93 volt in) for rated power into a 4 ohm
load.
Operation 13
1.
2.
3.
4.
5.