Power Line Noise

[Geoff]

In my experience, spike suppression using MOVs (line to neutral) is most beneficial and is a must for all equipment. I usually use them before the distribution block so that the whole system is protected at a single point. The points raised about failure are relevant, but these devices are so cheap that the can be replaced on an annual basis, or more frequently if your mains supply is particularly bad.

I do not believe that line input filters should be fitted to audio equipment, they should be limited to that for which they were designed, pcs etc. For a line filter to be effective it must have a significant impedance and increasing the impedance of the supply does nothing for the sound quality of the system. Also, having reduced the rf noise at the input, we then proceed to add some back in due to the rectification process. The place to filter out all rf noise is on the supply rails after the rectifier. This will reduce both ac borne and rectifier generated noise.

So far as noise on the earth is concerned, the best approach is to use, wherever possible, the computer environment arrangements of 'clean' and 'dirty' earths.

The suggestion of using an additional earth spike is, IMO, a complete waste of time. If I remember rightly, this was suggested some time ago in an article by Ben Duncan and it was claimed that the earth spike dramatically improved the bass definition. The resistance to earth of a single spike is going to be many times higher than the normal mains earth, particularly if the mains earth is bonded to incoming gas and water pipes etc, as it should be (though this is of less relevance in modern properties with plastic gas and water supply pipes).

I have tested a very, very large number of earth spikes on lightning protection systems and to get below a 10ohm resistance usually required an array of multiple spikes each 8 or 12 feet long. The number and length of the spikes depends on the soil conditions, but my measurements were made at several hundred different locations over a wide geographic area and so can be considered representative.

To put the matter even more into context, telephone exchanges required a central earth bar with a resistance to earth of less than 1ohm, before the supplementary bonding of incoming services. To achieve this resistance, the majority of sites required a grid of between 50 and 100 spikes. This is not feasible in the average domestic environment.

As it is unlikely that a single spike will make any difference to the earth impedance, the best approach is to ensure that all incoming services are adequately bonded and that the earth wiring resistance is minimised by uprating the cable size, if necessary, and maintaining tight connections.

Geoff

[Edited by Geoff on 08-30-2001 at 07:25 AM]

[haldor]

Originally posted by GRollins
Phil,
Conversely, a larger diameter wire carries high frequencies only on the surface, but low frequencies can permeate the entire wire cross section, leading to high frequencies only being able to use a comparatively small percentage of the cross sectional area compared to low frequencies
Grey

The point you are missed is that the volume of a wire increases as the square of it's radius. For example, the volume of copper in a wire more than doubles as you increase the radius from 4 to 6 mm. So even if the current is limited to traveling in the outer region due to a skin effect, there is actually more copper in that outer region than there is in the core. Again this is only for extremely high frequency signals which are easily filtered out by even the most rudimentory RF filters (The power transformer itself is probably sufficient to filter these frequencies).

Phil

[haldor]

Originally posted by Pete Fleming
G'day Grey,
It seems ironic that audiophiles as a whole latch on to simple things with dubious objective merit simply because they are easy to understand, yet ignore factors very much know to have a marked affect on the quality of the end product.

Peter I agree totally with you. I have seen people spend ridiculous amounts of money on speaker cables which they then use to drive speakers with passive crossovers in them. Why worry about a few milliohms of impedance in a cable or connector when the crossover is going to add 1000's of times that much impedance to the system (and as a bonus add some nasty phase shifting around the crossover frequency).

I have a confession to make. I'm an EE (electrical engineer) and my day job is designing signal processing equipment. A big part of what I have learned by doing this is to that it pays to look at systems in their totality and determine where improvements will give the biggest benefit before you start changing things. I often see a bad case of "can't see the forest for the trees's" from audio "tweakers". Once one part of the system has been improved it is a good idea to step back and reexamine the rest of the system instead of just mindlessly trying to keep improving the same thing over and over again. Fixation on one particular aspect of a system to the exlusion of the rest leads to very diminishing returns for your efforts.

It is human nature to feel that one is unique and has been given special knowledge that is only shared by a select few. Entire industry are built to cater (and profit) from this. A plausible explaination makes it easier to sell the latest $$$$ widget, so concepts are often borrowed from other disciplines that have no relationship to audio to explain the supposed benefit.

This is where concepts like skin effect in audio cables came from. In reality you have to get above 100 MHz before this effect becomes measurable and you only have to take it into account in your designs when you get are above a GHz. So obviously, skin effect must be the reason why those $2000 speaker cable do such a great job of "reducing the fractal component of the treble response thereby increasing the transparency and shimmering 3D imagery ..." I may want to copyrite that phrash, it could come in handy selling some widget I create in the future. ;^)

The fact is that electronics is a science not an art form. In reality, there isn't nearly as much mystery or arcane knowledge involved with designing audio gear as the average audiophile thinks there is. I can see it now, disclamers on the packaging "no amphibians where harmed in the making of this cable", I guess "eye of newt" is no longer the hot ingrediant. Both Douglas Self and Rod Elliot have sections about the excesses of the high end audio industry on their web pages, it makes for fun but infuriating reading.

http://www.dself.demon.co.uk/
http://www.sound.au.com/

Check it out with an open mind and see what you think.

[Pete Fleming]

Yes I agree. I find it intriguing that people would willingly pay 2000 British Pounds for a pair of interconnects (I’m presently looking at the advertisement), ignoring the fact that the signal has already travelled through many metres of PCB trace. As mentioned, I’m not suggesting the cables don’t make a difference, but why not instead upgrade the trace? When I was in the industry I would often solder wire onto the trace to repair a cracked PCB, so it’s certainly possible.

Having said the above, I must reiterate my stance that just because something cannot be measured doesn’t mean it doesn’t exist. Likewise, just because something has good specifications doesn’t mean it will be musically rewarding. Nevertheless I believe many manufacturers of audio accessory products really are treading a very fine line between fact and fiction. It seems we simply accept being lied to by manufacturers, passing it off as "marketing hype", however with the cost of some products becoming absurd is it time we begin asking for serious evidence to support some of the claims made? It seems a shame that some manufacturers are benefiting from such tactics, while others, possibly with genuine advances to provide, fail to remain profitable.

Cheers,

Pete

[GRollins]

Pete,
Yep, the pricing and hype on wire (and a lot of other audio stuff for that matter) verges on criminal. But as I've vented on this sufficiently elsewhere, I won't take up space here with it.
Now, I happen to agree with something that you said in an earlier post, to wit: Is skin effect just a convenient label for some other audible phenomenon? Quite possibly. After all, the numbers indicate that skin effect is of negligable importance at audio frequencies. Could it be that thin gauge (single or multi-strand) wire has some other effect? Dunno. Can't think of one. That doesn't mean that it isn't there. But in the meantime, I'm content to call it skin effect until someone comes up with a plausible idea that has a different convenient label. Yes, I'm aware that this is potentially counter-productive since, if you think you've got it tagged, you won't go looking for something new. But I hope that I'm flexible enough that if someone pops up and says,"You know this thing you've been calling skin effect? It's actually caused by a different effect," that I'll be able to absorb the new idea on its own merits.
Phil,
If:
a) The wire has x cross section and carries both a low frequency and a high frequency.
b) The low frequency has available to it the entire cross section of the wire.
c) The high frequency has available to it only, arbritrarily, 30% of the area of the cross section due to skin effect (for the moment, we'll set aside question of whether skin effect is an audible effect).
Then:
d) The resistance seen by the low frequency is determined by the resistivity of the metal used as a conductor, the length of the wire, and the entire cross section of the wire, whereas the high frequency has, by definition, a higher resistance due to the fact that it has available only a smaller portion of the cross section, since resistance is inverse to conductor area. (Your statement that volume increases with the square of radius is quite correct--you condemn your own argument with that one point. DC has all the wire, whereas high frequencies have only part of it...so the larger the wire, the more pronounced the difference between DC [or low frequency] and high frequency conductivity.)
If you truly feel that your conclusions regarding skin effect and proper gauge of wire are correct, then rush to the patent office and lock it down in your name.
Geoff,
It'd be nice if MOVs had some form of indicator--perhaps changing color due to the heat dissipated?--that would serve to indicate when they were beyond their useful life. That would help take the guesswork out of when to replace them. I have no opinion, myself, on audibility of MOVs, but have noted that some people (I think Phil mentioned this above, and perhaps others) think that they have deleterious effects on sound quality. Unless and until I play with them, I'll refrain from taking either side of the debate.
Note that I'm not necessarily saying that a ground spike will make someone's system sound better. I just happened to remember my friend's system, and even then he only put in the spike because his house was old enough that he had ungrounded sockets. An electrician told him it'd be easier than running fresh wire all the way back to the breaker box. I don't recall whether there was any difference (bass, silence, or any other characteristic) in the sound. He was revamping his system at the time, and any sonic effect (good or ill) was swamped by all the other changes he was making.
The resistance to ground through a ground spike might be higher...granted...but if it's to a 'quiet' as opposed to a 'noisy' ground, it might still lead to an improvement. What do you think?

Grey

[haldor]

Originally posted by GRollins
Pete,
he only put in the spike because his house was old enough that he had ungrounded sockets. An electrician told him it'd be easier than running fresh wire all the way back to the breaker box.Grey

Ouch! That is a serious code violation and could get someone killed. The reason for the ground in a wall outlet is not for noise control but to provide a redundant return path for fault currents so the circuit breaker will trip in case of a wiring failure inside the protected equipment.

The only safe way to use the older 2 prong wall outlet with modern metal cased equipment is to use a cheater plug that has the ground pigtail wire connected to the center screw of the outlet (which per NEC code is supposed to be connected back to the breaker panel ground bus). A seperate gound rod may have too much impedance between it and breaker panel to trip the breaker during a fault condition. If this happens the person who touches any metalic part of that gear is going to get shocked, potentially fatally. This is the reason why guitarists keep getting electrocuted during gigs. They love to use old tube amps that don't have proper safety grounds and when something goes wrong inside the amp they become the ground path.

Your friend got seriously bad advice.

If you really want to clean up your power wiring and are willing to pay a few bucks to an electrician, have him run a dedicated circuit (line, neutral and ground) from it's own circuit breaker directly to your audio equipment and don't plug anything else into that power outlet. I routinely specify this for data collection systems installed in factories (I was a field service engineer before I got into design) and it helped reduce ground noise which is a real problem when measuring small signal levels, thats also where I first learned about MOV suppressors polluting grounds.

Phil

[Thoth]

Originally posted by Geoff
I do not believe that line input filters should be fitted to audio equipment, they should be limited to that for which they were designed, pcs etc. For a line filter to be effective it must have a significant impedance and increasing the impedance of the supply does nothing for the sound quality of the system. Also, having reduced the rf noise at the input, we then proceed to add some back in due to the rectification process. The place to filter out all rf noise is on the supply rails after the rectifier. This will reduce both ac borne and rectifier generated noise.

Currently, all my equipment is commercial off-the-shelf (Parasound, NAD, Denon and Sony). None of it is modified. In this case, the only way to get rid of the power line noise is externally. The line filters I'm using have current ratings significantly in excess of the current draw of my amplifiers. This was intentional, for the purpose of minimizing the increase in impedance of the power line. Also, I placed significant amounts of capacitance (0.22uF) across the power line, as it should help to remove noise, without increasing the 60Hz impedance.

If I were building my own equipment, I'd certainly do my best to add adequate noise rejection to the power supply. This would include large capacitor banks, bypassing with film capacitors, and an inductor (PI filter). I agree that it is better that way.

[Geoff]

Thoth

You have a valid point about commercial equipment. Internal modifications play havoc with the warranty. I must remember in future not to overlook the problems associated with off-the-shelf units, even though this is a DIY forum.

Geoff

[Thoth]

Originally posted by Geoff
You have a valid point about commercial equipment. Internal modifications play havoc with the warranty.

The warranty isn't the issue. In my power amps (where external filters have the largest negative impact), there's not enough room to do much. Commercial equipment is made as small as possible, to save on cost.

On the other hand, DIY equipment doesn't usually worry about space. If you find you need a change, there's usually room to make it.