QUALIA & Co INDIGO Series Owner's Manual - page 15
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There are many possible causes of humming noise or other noise.
The INDIGO PHONO is a wide-band amplifier. It is sensitive to high-frequency noise generated on the power supply
and digital noise generated on line cables. These noises are generated by various factors.
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Digital noise often found on CD players, D/A converters, and PCs greatly influence phono equalizer amplifiers,
preamplifiers, and power amplifiers of a system.
In order to prevent negative influence of such noise on other equipment, take the power from an adequate place and
use a power strip or isolated power supply equipped with a noise filter.
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Noise may come from a line cable.
Extra attention to noise is necessary when an unbalanced cable is used. Some cables are not very resistant to noise
(often expensive cables). Noise sometimes disappears when an ordinary cable is used.
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Take consideration for ground loop.
Recently, power cords with grounding are often used. When many such cords are used, a common ground is used
for equipment connected to a power outlet and a complicated ground loop is generated due to relationships with
signal cables. As a result, a humming noise is sometimes generated of which the cause is hard to identify. In this
case, attach a three-prong to two-prong adapter to create a floating ground. This is a problem in the entire system.
Try it on the phono equalizer amplifier (INDIGO PHONO), preamplifier, and power amplifier to find the best position.
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When a metal rack is used, cables making contact with the rack sometimes negatively influence the entire system.
Install cables so that they make an arc without making contact with any metal parts of the rack. If cables are heavy,
lift them by placing a woodpiece or something similar between the cables and the rack.
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When humming noise or other noise is generated
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Maintenance
Before servicing or moving this device, be sure to turn off its Power switch, pull out the power plug from
the wall socket, and disconnect external connection cables. Damaged cords can cause fire or electric
shock.
To clean this equipment, wipe it with a soft cloth such as commercially available cleaning cloth. When
the device is extremely dirty, gently remove dirt using a soft slightly dampened cloth. DO NOT use acid
detergent or solvent such as benzene and paint thinner because they damage the cabinet.