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In Reply to: Can you "amplify" on your statement? posted by Lew on March 16, 2004 at 07:26:32:
We are talking at cross-purposes, Lew. The Power Wraps product I'm talking about (see url)
comprises a pair of stiff spirals of specialized wire. One places them around the power cord
and adjusts the position to kill the RF standing wave on the power cord. They are made
under license from Don Palmer, retired owner of HighWire Audio cables. Don was an
aerospace engineer and had to deal with RF standing waves in satellites, etc.Any short piece of wire terminated by impedance mismatches is an RF resonator. Audio
cables and power cords qualify, as they are typically terminated without regard for
transmission line impedance matching. By analogy, any short piece of empty pipe (such as
a flute) is an audio resonator, whether the ends are open or closed.What this means is that any source of RF energy within or around the piece of wire will set
up a harmonic series of standing electrical waves that are in the radio frequency band
because of the short length of the wire. In the case of the power cord, even if the power
outlet from the wall is perfectly filtered, any broadband content in the current drawn by the
equipment, such as the Fourier components of the current wave form through rectifiers into
capacitor-input filters, or RF energy generated in nearby equipment, will stimulate the series
of RF standing waves. By analogy, air blown across the end of the pipe (the flute's
mouthpiece) will set up the pipe's characteristic tone (with harmonics).The RF standing waves exist in the space around the wire, so placing something that draws
in their magnetic fields (i.e. with high permeability) and that has sufficient resistance
(dissipation) lowers the "Q" of the resonator so that it is difficult to make it ring. By analogy,
stuffing the pipe with rags makes it hard to generate a tone, no matter how much acoustic
energy is applied at the end.As Ralph said, replacing standard silicon rectifiers with HexFreds helps, because they
generate less RF energy when they shut off. However, they still cause a very steep decrease
in power circuit current when they shut off, and this steep waveform has many high
frequency Fourier components. Therefore, typical Atma-Sphere power supplies will cause
RF ringing on the power cords.Different equipment has different levels of sensitivity to the RF standing waves on the power
cords. In my experience, the Wadia 861 is very sensitive, and I'm in the middle of a search
for the ideal power cord for this device. My limited experience with the MSB CD Station
showed that it is much less sensitive. This might be why some folks think it has better
inherent detail retrieval than the Wadia. My MA-1s are also very slightly sensitive to
addition of Power Wraps to the power cords, but I've been limited by the need to have two
cords to do a proper evaluation, so I can't say whether the Silent Source or Virtual Dynamics
Master cords improve the sound over stock cords with Power Wraps on them.Audio is a game of inches, so even if the equipment is insensitive in itself, the mere
presence of the standing wave on its cord has some influence on other equipment in the
system. This is why it is worthwhile to experiment with all the power cords. The Power
Wraps are relatively inexpensive, and can show where more exotic cords might be useful.As should be obvious, I'm not a dealer for Power Wraps devices. Don Palmer is a neighbor:
he lives in that snotty valley next to ours that thinks it knows how to make wine, but I don't
hold that against him.
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Follow Ups
- Re: Can you "amplify" on your statement? - Al Sekela 09:22:59 03/16/04 (1)
- Glad I asked - Lew 11:14:30 03/16/04 (0)
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