Australian Monitor SY800 - Manual (Page 17)

Australian Monitor
Operation 17
of 600 Ohms or lower to avoid unwanted high
frequency loss in the cabling.
Input overload occurs at +20.5dBu (8.25 volts).
Most equipment is designed for minimum hum when
used under ideal conditions. When connected to
other equipment, and to a safety earth in an
electrically noisy environment, problems may occur.
The three "E"s of hum and hum related noise which
can plague your audio system are:
a) Electrostatic radiation,
b) Electromagnetic radiation, and
c) Earth loops
radiation capacitively couples to
system elements, causing an interference voltage
that mainly affects higher impedance paths, such as
amplifier inputs. The source is generally a nearby
high voltage, such as a mains lead or a speaker lead.
The problem can usually be reduced by moving the
offending lead away, or by providing additional
electrostatic shielding (i.e. an earthed conductor
which forms a barrier to the field).
radiation induces interference
currents into system elements that mainly effect
lower impedance paths. Radio transmitters or stray
magnetic fields from mains transformers are often
the cause of this problem. It is generally more difficult
to eliminate this kind of interference, but again,
moving the source away or providing a magnetic
shield (i.e. a steel shield) should help.
can arise from the interfacing 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:
Hum Problems
Electrostatic
Electromagnetic
Earth loops
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.
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.
Ensure that balanced signal leads connecting to
the amplifier are connected to earth at one end
only.
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 Synergy 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 to the
amplifier.
Always ensure that your amplifier is
and the
attenuators are when you engage this switch.
This switch should only be used when the amplifier is
operated from a
signal source.
NOTE: Be wary of outputs, these
are often no more than floating outputs.
Signal Ground-Lift Switch
off
down
balanced
quasi-balanced
unbalanced