You may just want to think twice before you shell out a few hundred dollars or more on those new “high end”audiophile power cords. Bryan Geyer explains why!
An AC power line cord should simply serve as a lossless link between the AC source inside your wall and the DC power supply stage inside your audio equipment; converting raw alternating current to clean, usable direct current- the power that runs all of the ensuing circuitry – is best enabled inside the product’s internal power supply. This is where the requisite processing should be applied because that’s where all of the specialized components are located.
A modern solid state linear DC power supply utilizes full wave rectification with very heavy filtering. EMI and RFI bypass traps are provided at the supply input, to shunt high frequency noise to ground. Active components are utilized to enhance DC stability. Zener diodes clamp voltage levels and chop ripple. Precise series regulator stages are implemented where there’s justifiable merit.
Consequently, the output is scrubbed free of all extraneous AC artifacts—giving us just plain/pure/flat/steady direct current, and one can view that flatline pool of DC power by observing the waveform on any basic 50 MHz oscilloscope.
THE KISS AC LINE LINKAGE
The “KISS” approach should be used as an appropriate guideline for AC line linkage. Even so, one can definitely find many misguided schemes that are intended to “pre-purify” the external AC supply which in my opinion, offer little significant benefit.
A simple “KISS compliant” AC line cord is what your a product designer would be expected to use. However, that line cord may not necessarily be blessed by many of the so called “groupthink gurus” at your local audiophile club. As is now the current trend in high end audio, many enthusiasts are prone to suggest using some of the exotic accessory cords currently available; e.g.: a Teflon double-wrapped power cord composed of 54 fine strands of silver-clad, oxygen-free high-purity copper configured as a dual-braided AWG 8 conductor that may indeed cost about $600/meter. (And is about as flexible as Romex.)
Most audio devotees reading this are well aware on the considerable amount of highly praised and priced audiophile power cords that are currently available on the market. Others will further claim that their preferential exotic power cord will, without doubt, “blow away” the KISS cord, comparatively speaking within a specified set of subjective listening tests. However, I believe one should always try to apply some calm to these suggestions and initially try to just use the KISS cord. You can be rest assured that it will indeed perform as the desired near-lossless link and that it will present no impact on any aural aspect of the product in question. In fact, it is totally outside the audio signal path.
One of the most effective means to route AC line current to the internal DC supply stage would simply be to extend the existing AWG #12 or AWG #14 Romex power line from the wall, so that it can then reach the AC input port on your equipment. After all, solid AWG 12 or AWG 14 pure copper Romex is an almost perfect AC power line cable with current carrying capacity limited only by its intrinsic series resistance.
NO TO ROMEX?
Of course, Romex isn’t normally acceptable because solid wire is quite stiff and inflexible, so AC power line cords generally utilize stranded copper wire, of a suitable diameter, to tie the equipmen to the in-wall supply line. The original circuit designer will select a gauge (AWG) appropriate for the required capacity.
If you have good reason to want a longer or shorter cord, or one with an angled C13 connector (to reduce rear clearance), simply let the designer’s AWG be your guide. You can always increase the conductor gauge if you have to extend the length of the cord well beyond its original reach—or do so simply because you want to upgrade; this will be your decision.
If we take an in depth look at many of today’s power amplifiers, the stock AC line cord diameter is generally AWG 16; its length 2 meters. This would be adequate for a “mid-market” solid-state power amp that can drive 200 Watts/channel into 4Ω loads with a typical power consumption of ~ 700 Watts at full output. With AC line current drain running ~ 5.83 Amperes, the voltage drops across the power cord’s internal resistance (0.0263 Ω) and would then be some 153 mVrms—that’s pretty negligible. If you would prefer to upgrade to something more substantial then simply just move up to a 14 AWG diameter power cord, and buy it to fit the required distance. A 14 AWG power cord has a basic wire resistance that’s ~ 37% < 16 AWG cord.
With respect to insulation, the industry standard for heavy-duty prime commercial AC power line cordage is type SJT, with a molded construction. (Type SVT is a lighter standard.) Type SJT is quite excellent. This wire standard (and the wire gauge) will be printed directly onto the cordage itself, so you can easily view what you’ve got.
Enthusiasts should always be aware that you can buy top quality molded SJT power line cords, AWG 14, 16, or 18, of any length, made to utilize your personal choice of C13-type female connector (straight, angled left, or angled right*) on line. The cost for this custom cord will be minuscule when compared to many of the most highly touted “audiophile-grade”cords but in fact, will be a direct functional equivalent and of the exact desired length— no need to hide coiled-up excess. Always utilize basic AC surge protection; it might help in the event of a power line aberration.
*Note: Consider the use of an angled C13 connector if you encounter a depth fit problem when positioning a power amplifier.
EDITOR’S Addenda: When further discussing this issue of hi-end AC line cords with our author, Bryan replied…
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