AUSTRALIAN MONITOR AM2600NG Руководство по установке и эксплуатации - Страница 8

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1. Specifications

INSTALLATION

Speaker Connector Wiring Diagram

Hum Problems

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,

c) Earth loops

Electrostatic 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).

Electromagnetic radiation induces interference currents into system elements

that mainly affect 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.

Earth loops can arise from the interfacing of the various pieces of equipment

and their connections to various safety earths.

PAGE 8

Hum Problems continued

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:

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.

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 AMNG 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

willensure the shield on your input wiring actually goes to the ampliﬁer

chassis and subsequently to earth.

IMPORTANT: 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 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.

AM2200NG & AM2600NG INSTALLATION AND OPERATION MANUAL