I use cheater plugs for hum reduction. To understand why, we must enter the
realm of Engineering Philosophy. While I have only a few really high end
components, I am very fond of three old surround processors, two external
DACs, two analog preamps, five basic amplifiers, and miscellany. The more
parts in the system, the harder it is to deal with audible hum. As the
Jensen article points out, it is virtually impossible to eliminate hum
loops
when unbalanced interconnects are used.
Nevertheless, at one point, my system was pretty hum-free even though two
components, an Acoustat TNT-200 and a Hafler pre have three wire power
cords. Then, one day, it was back. I went through the drill of
disconnecting
pieces until the hum went away, but it did not. Facing a very simplified
system, I stared in astonishment at the Parasound SCAMP power switchers,
which I had installed to be "green." I took them out and the hum went
away.
Apparently, the relay contacts had unbalanced the potentials in a very
slight way, enough to increase the level of hum significantly. I don't
know
whether it was contact resistance or contact rectification. But my
conscience would not allow me to live without the SCAMPs in the system.
Putting a cheater plug on the Acoustat amp knocked the hum down.
From the dawn of the electrical age, people have lived with single levels
of
protection in consumer electrical equipment. Residential table and floor
lamps are vulnerable to internal shorts that can put lethal potentials on
the metalwork. The National Electrical Code continues to allow this
because
such lamps are supposed to be used in rooms with little exposure to
electrical grounds. Following a similar philosophy, amplifiers built until
the 90's frequently had two wire cords. Such amplifiers are still in wide
use.
More recently, the NEC reflects a preference for two levels of electrical
protection. Although the NEC sanctions only passive measures, such as a
protective ground, or special transformer construction known as "double
insulation", a GFCI (Ground Fault Circuit Interrpter) replaces the
protection lost by disconnecting the protective ground with a cheater a
plug. It could be argued that, since the GFCI is an active device, it is
not
as reliable as the passive protection provided by a passive ground.
However,
such arguments are difficult to quantify. The GFCI detects a problem
anywhere in the system, while the Acoustat passive ground protects only
the
Acoustat. The GFCI detects nascent problems, while the protective ground
can
silently mask transformer leakage until the transformer burns up.
Audiophiles face a serious challenge in eliminating hum from their
systems,
because the interconnect system devised seventy years ago looks fine, but
it
doesn't work reliably. It works best when components made by the same
manufacturer are hooked together in simple configurations. Those who
prefer
to mix/match among manufacturers and genres according to their taste can
encounter apparently insuperable obstacles. It is much to the shame of
consumer hi-fi manufacturers that they did not adopt professional balanced
standards. This will become moot in the transition to an all digital
world,
but it doesn't help those of us who have substantial investments in
equipment that may have sonic virtues.
Bob Morein
(310) 237-6511
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