AUSTRALIAN MONITOR IS1200, Инструкция по установке и эксплуатации

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Earth loops can arise from the connection of the various pieces of equipment
and their connections to various safety earths. This is by far the most common
cause of hum and it occurs when source equipment and the amplifier are
plugged into different points along the safety earth where the safety earth
wiring has a current flowing through it. The current flowing through the wire
produces a voltage drop due to the wire’s resistance. This voltage difference
between the amp earth and source equipment earth appears to the
amplifier’s input as a signal and is amplified as hum.
There are three things you can do to avoid earth loop problems:
1. Ensure the mains power for the audio system is “quiet” i.e. without
equipment on it such as air-conditioning, refrigeration or lighting which
may generate noise in the earth circuit.
2. Ensure all equipment within the system shares a common ground/ safety
earth point. This will reduce the possibility of circulating earth currents, as
the equipment will be referenced to the same ground potential.
3. Ensure that balanced signal leads connecting to the amplifier are
connected to earth at one end only.
Signal Ground-Lift Switch
When proper system hook-up has been made, you may still have some hum
or hum related noise. This may be due to any of the previously mentioned
gremlins. Your IS Series amplifier has a “Signal Ground Lift” switch which
disconnects the input ground wiring from the amplifier. A substantial drop in
hum and/or hum related noise can result from the judicious use of this switch.
NOTE:
If the input ground lift switch is used, you must ensure adequate shielding of
the input wiring. If the signal source equipment does not provide adequate
shielding (i.e. a definitive connection to ground), you must disconnect the
shield from the input connector’s ground pin (Pin-1) and re-connect it to the
”drain” contact on the input connector. This will ensure the shield on your
input wiring actually goes to the amplifier chassis and subsequently to earth.
DO NOT CONNECT PIN-1 DIRECTLY TO THE DRAIN CONNECTION.
You will defeat the amplifiers internal grounding scheme and possibly cause
instability in the amplifier. Always ensure that your amplifier is off and the
attenuators are down when you engage this switch. This switch should only
be used when the amplifier is operated from a balanced signal source.
NOTE:
Be wary of quasi-balanced outputs, these are often no more than floating
unbalanced outputs.