ALLEN & HEATH iDR-4 User's Guide download pdf (Page 15)

iDR-4 User Guide 15

Earthing

The connection to mains earth (ground) in an audio system is important for two reasons:

Safety - To protect the operator from a high voltage shock associated with the AC mains supply

feeding the system.

Audio Performance - To shield the audio signals from interference pickup and to minimise the effects

of ground loops which result in audible hum and buzz.

Earth is used to shield audio cables from external interference such as the hum fields associated with

power transformers, lighting dimmer buzz, and computer radiation. Problems arise when the signal

sees more than one path to mains earth. An earth loop results causing current to flow between the

different earth paths. This condition is usually detected as mains frequency audible hum or buzz. To

ensure safe and trouble-free operation we recommend the following:

Do not remove the earth connection from any iDR unit mains plug. The chassis of the unit is

connected to mains earth through the power cable to ensure your safety. Audio 0V is connected to the

chassis internally. If problems are encountered with earth loops use ‘ground lift’ switches or adaptors

on connected equipment accordingly, or disconnect the screens from interconnecting audio cables at

one end, usually at the destination.

Use a clean mains supply for the audio system. Ensure the audio mains supply is run separately

from lighting, motor, kitchen equipment and any other potentially noisy mains supplies. Use a mains

filter and surge protector for the audio supply if necessary. Take care to ensure good earthing in

distributed systems such as those with audio units linked over long distances.

Connections and Cables

Use professional quality cables and connectors and check for accurate wiring and reliable solder

joints.

Avoid running audio cables alongside mains, computer or lighting cables or near thyristor dimmer

and power supply units. If unavoidable, cross the cables at right angles or run them in separate

screened trunking to reduce the interference pickup.

Use low impedance sources such as 600Ω or less microphones to reduce susceptibility to

interference. The outputs of the iDR are designed to operate at very low impedance to minimise

interference problems.

Use balanced connections where possible as these provide further immunity by cancelling out

interference that may be picked up on long cable runs. To connect an unbalanced source to a

balanced Mic/Line input link the cold input (XLR pin3) to 0V earth (XLR pin1) at the unit. To connect a

balanced Line output to an unbalanced destination, link the cold output to 0V earth at the iDR unit.

Backup Power Supplies and Safety Standards

The iDR system is designed to conform to internationally accepted safety standards IEC60065 and

UL6500. It uses a built-in mains voltage power unit to supply the various internal power rails. It is

recommended that the iDR system be backed up using a UPS (uninterruptible power supply) in

installations where public safety is at risk. This is a requirement when an alarm or voice evacuation

system is integrated.

WARNING: For safety it is important that all equipment earths are

connected to mains earth so that exposed metal parts are prevented from

carrying high voltage which can injure or even kill the operator. The installation

engineer should check the continuity of the safety earth from all points in the

system including microphone bodies, cables, racks and equipment panels.

Check which safety standards apply to your installation. A backup UPS

supply may be required. The standards may also apply to the grade of cable and

installation methods required.

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ALLEN & HEATH iDR-4 User's Guide Page 15

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