The Truth About Interconnects and Cables - page 6

Power Leads

The power lead (cord or cable if you prefer) is how mains power at 220V, 240V, 110V at 50 or 60Hz gets to your system. The specifics of the voltage and frequency are determined by where you live, and the available household mains provided by your electricity company.

There are mains cables (power cords) available that defy belief. Would you spend US$3000 for a 2 metre mains lead? You can buy a very nice amplifier indeed for this sort of money, but they are there, and someone must be buying the stupid things.

What possible effect 2 metres of flexible cable can have to counteract the kilometres of power company's wiring is a simple question to answer. None. Or, to more precise, none whatsoever. I am not referring to cables with inbuilt filters or other esoterica here, just perfectly ordinary mains leads.

I have measured the distortion on the mains at my workshop test bench. Last time I did this it was 5.6%, and there is absolutely nothing that a cable can do to change this, regardless of cost. The distortion is caused by a multitude of things completely outside our control, with power supplies for computers and other equipment being only one group of offenders.

These draw power at the peak of the AC waveform, causing it to become flattened (similar to clipping in a power amplifier). The various power company transformers along the way will also introduce some degree of distortion, and there are inductive and capacitive losses within the distribution system. As well, there are large motors being controlled by various speed controllers (most use large solid-state switches), used in industry and commercial centres. Lifts, air compressors, machinery, the list is endless.

Because of the resistance of the supply authority's cabling and transformers (there are some massive cost considerations they must address), when a high power appliance is turned on, the mains voltage falls. This resistance (actually it is impedance) will cause the voltage to vary from one second to the next, with significant drops at the times when meals are being prepared (electric stoves switched on all over the place), and at other periods. I have measured the impedance at my house at 0.8 Ohms (we use 240V in Australia ), so an appliance that draws 10 Amps (such as a heater) will cause the voltage to fall by 8 Volts. This could be reduced by increasing the size of my internal wiring, but the gains would be few and the cost high. In 110V countries such as the US , the wiring impedance must be made lower, since all currents are higher for the same power. It is likely that this causes even greater compromise due to the larger wire sizes that must be used (larger wire means greater cost).

So, given that the mains is distorted, and varies in amplitude from minute to minute throughout the day, and has significant impedance, what can be done to fix this? One method would be to use an Uninterruptable Power Supply (UPS), which (if you get the right type) uses the incoming mains to charge batteries, then uses an inverter to supply power to your equipment. You can buy one of these for $3000, and the emerging mains supply will be as clean as the UPS can make it. No cable can do this, regardless of price.

Using a UPS will ensure that your 100W amplifier can provide 100W, despite the variations in the supply voltage. Whether you can hear any difference is doubtful, because even given that the mains can (and does) vary by up to 10%, your equipment should have a reserve power rating that can accommodate such variance.

I have been advised by a reader (in the US ) who reminded me that unless the UPS is specifically designed for sinewave output (and the distortion is quoted), it will probably have greater distortion than the mains anyway. The voltage will be stable, but the switching noise of the UPS may actually make matters worse.

A 100W amp (at nominal supply voltage) should give at least 100W. At 10% low supply, this drops to about 80W, a difference of less than 2dB. If you are operating power amps at close to clipping all the time, you will hear the difference, but this is not the way Hi-Fi gear is meant to be used.

Q: Having a nice clean sinewave from the UPS or power conditioner should make a difference though, shouldn't it?
Q: Why would it not make any difference to the sound from the amp?

The answers are simple and complex, but the result is the same. At the very best, transformer dissipation might be slightly lower, but the AC from the secondary of the transformer is rectified and filtered, making it into DC, since the amp cannot operate from AC power supplies. The amount of DC "ripple", or superimposed AC signal is determined by the design of the amplifier's power supply, and is completely independent of outside influences other than the mains supply impedance. Even this has a very minor effect in the greater scheme of things.

If I really wanted to be able to supply 100 Amps to my speakers for brief moments, my power supply can already do this. If I wanted to be able to do it all the time for extended periods, my speakers would catch on fire. No mains lead will give my power supply this ability, nor take it away. The limitations are in the supply itself, and include the transformer, rectifier and filter capacitors.

One useful observation is that the mains in the US seems to be basically pretty nasty, and not at all what we are used to in Australia . Interference seems to be a major problem, and if this is the case, it will find its way through the power supply and into the amplifier (or other equipment) if the power supply is not well designed.

Also, because of the lower mains voltage in the US (nominally 120V), the current drawn by power amplifiers in particular can cause real problems with cheap light duty cables. I have already made this point, but it is worth making again. Use of a heavy duty lead (possibly shielded if interference is a problem) will make a difference. Whether the power difference is audible or not is debatable, but elimination (or even reduction) of mains borne interference is likely to result in a worthwhile improvement in sound quality.

Normally I would expect that any interference would be audible all the time, and it seems very unlikely that it only manifests itself when there is music playing. Electricity is not that cunning, and is not by nature vindictive. Having said that, it must be noted that when an amplifier is producing a lot of power, the current spikes on the mains will be much greater, and may have an influence that would normally be un-noticed. The easy way to determine this is to move the leads about to find out if this changes the background noise level. If it does, then re-locating the leads will provide far greater benefit than spending a king's ransom on power leads.

Use of a proper power conditioner (or a "pure" sinewave UPS) will completely eliminate mains interference, and this will naturally be beneficial. This is not something I have encountered, but if there is a problem, then this is probably the best way to fix it.

In some cases, all that may be needed is interference suppressors ("spike arrestors"), to get rid of clicks and pops that get into the system via the mains. These are readily available and fairly cheap, and might be a good place to start.

I have examined several mains leads I have, and upon inspection I saw that the pins of the US plugs are of thin sheet metal (brass). This is folded over for the flat pins (active and neutral) and rolled into a tube for the earth pin. In contrast, our (Australian) plugs have solid brass pins, and are altogether much more substantial than the US ones (the US lead I have is rated at 13A, and is a very solid cable - but the pins are a weakness IMHO). The standard 13A fused UK plug is even more solid than ours - the pins are probably capable of at least 50A based on their size. One style of European style plug I have is also nice and solid. Elsewhere, I do not have samples, and can't comment.

To give you an idea. Listed below are the pin sizes and materials for 4 mains plugs I have

As you can see, even though the US lead has a higher current rating and requirement, the pins are smaller and capable of less current. Where the others use solid brass pins, the US lead has thin sheet brass folded over to give a thicker overall pin - which is still thinner than the others. It is also wibbly - you can quite easily bend the flat pins with your fingers - I did ! Bent them right over at the base, and bent them in the middle. This is impossible with any of the others. From what I recall of US wall outlets, they are also fairly wimpy affairs, with relatively poor contact surfaces.

Another point mentioned was that by using a high current shielded cable for the mains may prevent the current spikes caused by the amplifier's rectifier from injecting spurious noise into interconnects and other equipment. There may be some truth in this, and the effects are certainly measurable - this is why professional audio gear uses balanced connections, to eliminate exactly this sort of problem. Use proper "lead dress" - keep all power leads as far as possible from signal interconnects, and if they must cross, then cross them at right angles.

It also seems that the regulations in the US as to what you may (or may not) use as a power cable are somewhat lax (by Australian standards, anyway), allowing sub-standard connectors at both ends of the cable, and with seemingly minimal control over what may legally be sold as a mains lead.

Many (most?) of the high-end cables that I have seen referred to would not be legal in Australia , and in many other countries. No mains lead is allowed to be sold here without electrical authority approval - this is quite expensive to obtain, and involves voltage drop testing (the lead's resistance) and electrical insulation tests, along with various others. Shielded mains lead is uncommon, but I am sure that it would be available.

I have been taken to task seriously by some for not having tested any of the mains cables - well I can't, because I (like everyone else) have no criteria to base tests on. I know from experience that long (or light duty) leads will reduce the power available, but have no way to create interference of the type that could cause severe sonic degradation so I can verify that a cable eliminates it.

As to blanket claims that "the power cord has more influence than anything else in the chain other than room positioning of the speakers" (and yes, someone did make that claim), what can I say?

One of the respondents is apparently a distributor of high end power leads (so I discovered from someone else's posting), and he had no proof to offer, and nor did anyone else, so I am still left with the same conclusion as before (with some modification based on interference problems).