ISP SERIES
INSTALLATION AND OPERATION MANUAL
INSTALLATION & SETUP (CONT.)
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) Earth loops
b) Electromagnetic radiation
c) Electrostatic radiation
Earth loops 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:
• 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.
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 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.
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” (ungrounded) 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 ISP Series 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.
• Ensure that all system grounds (earth) 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.
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.
SENSITIVITY
The input sensitivity for your ISP amplifier configured to a factory default setting is:
1Vrms for rated power into a 4Ω load
Each channel of your ISP amplifier has a nominal balanced input impedance of 10kΩ (@1kHz) and should not present a difficult load for
any signal source.
Your signal source (i.e. the equipment feeding signal to the amplifier) should have an output impedance of 600Ω or lower to avoid
unwanted high frequency loss in the cabling.
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