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Introduction iv
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©2004 PS Audio International Inc. All rights reserved.
Introduction
Owner’s Reference
Humbuster III
Thank you for your purchase of the PS Audio Humbuster III.
The Humbuster is designed to block DC voltage on the AC line. DC voltage on the AC line can
cause mechanical hum to appear in your equipment. Mechanical hum is described as being that
noise generated by the power transformer inside a piece of AV equipment.
The Humbuster will have little effect on hum and noise heard through the loudspeaker or
headphones. In some instances, it is possible that the reduction of mechanical noise in the
unit’s internal transformer may reduce the magnetic field of the transformer and thereby reduce
hum heard through a loudspeaker.
All AC power lines have a small component of DC (battery type voltage) on the line. Typically this DC
is held to a very low level and causes only a few problems. However, many homes AC performance
is not “typical” and this DC component can be quite high. In fact, it’s high enough to cause an
asymmetry that “pushes” the voltage in the transformer in one direction and partially saturates the
core of the transformer, causing it to buzz. In addition to buzzing noises, the transformer is also at a
performance disadvantage because its core is not working properly.
Transformers work best when there is absolutely zero DC presented to them. This is because
transformers are AC devices, not DC devices. Transformers need to change the direction of their
magnetic fields multiple times per second in order to function properly. When there’s DC on the line,
it forces the transformer to stay polarized in one direction and this make the transformer a little crazy
- and it hums and complains in response.
The Humbuster removes the DC component from the AC line and either stops or significantly
reduces the buzz and vibrations caused by DC. How effective the HB-III is depends on just how
much DC there is on the line and what the quality of the transformer inside your unit is.
Humbusters work by placing a simple network of power rectifiers and power capacitors in an
arrangement that removes the direct coupling at the AC’s zero crossing point. This blocks the DC
from coming through. Then, just a volt or so above and below the zero cross point, we direct couple
the AC signal back again. It’s simple, yet effective.
What will it do?
DC Voltages
Transformers
How it works
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