Testing power leads with non contact ac detector

Rambles

Distinguished Member
Is it worth it, or is it nonsense?

This guy seems to suggest that they shouldn't 'leak':


A non contact AC detector is an inexpensive item to buy, so I could get one and test to see if any of my cables are 'leaking'. But I am confused as to whether that is a meaningful test. I suppose it is showing that if electrical noise is getting out, then they aren't very well shielded, and it might be worth changing them for better shielded ones.

Any views anyone?
 

Rambles

Distinguished Member
Its not April's fool yet is it ?
:) Actual genuine question though!

Should power leads leak? Or, it doesn't matter? Shielding not necessary? Wrong type of shielding?
I don't know, seemed likely to me.
 

Barcoing Mad

Active Member
In short: these probes act as capacitive sensors of a nearby AC voltage. A screened cable effectively stops any voltage being induced across the probe. It isn't noise, which by definition is a superposed random signal.

Understanding Capacitive Voltage Sensors

When the positive and neutral lines of the power lead are plugged into a bluray player or whatever, they're going to be feeding a switch mode supply. These supplies generate plenty of crud - but good design filters this out of the DC lines supplying the internals.

Screened power leads are going to make balls all difference.
 
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ChuckMountain

Distinguished Member
Sorry meant more the video, than your question.

It's the pseudo science bull that I can't stand. :devil:

The "leak" is a property of an electric field produced by AC in a wire. It's this that non-contact voltage detector is picking up and is perfectly normal behaviour.

The cables in you walls up to the socket are non-shielded so just having shielded cables (what are the shields connected to?) isn't necessarily going to stop these leaks

You can of course get shielded power cables but whether they produce any noticeable or audible difference is between you and your wallet :p
 

Rambles

Distinguished Member
Okay, thanks both!
 

Abacus

Banned
Providing the cables meet the power capacity of the equipment, and relevant EU/UK electrical safety regulations, (The supplied cables always do) then it won’t matter whether they come free with the equipment, or are made from star dust and cost £10,000, there will be no performance difference between them, so don’t fall for the rubbish that HiFi cable manufactures come out with to con you into buying their cables.

Hope this helps

Bill
 

ChuckMountain

Distinguished Member
Ahh but those made from black hole dust, just seem to suck all that noise and stuff away, just like errr a black hole :thumbsup:
 

Rambles

Distinguished Member
Thank you, I like what I am hearing, it sounds inexpensive! What about shielding? I know that if the guy over the road cuts his front lawn with his petrol mower, I lose my Freeview signal in the lounge! Are mains leads not susceptible to the same affect as an aerial lead, maybe?

Thinking along the same lines, if the mains lead are 'leaking' through poor shielding and are close by to a speaker cable or interconnect, could the other cables be 'infected / contaminated' by the mains cable if it isn't properly shielded.

I know that you are supposed to keep mains leads away from other leads, but it's just not practicable to do so in my set-up.
 

ChuckMountain

Distinguished Member
Sounds like something is wrong with the mower. It might need a filter on it, they are available.

The aerial is doing what it supposed to and picking up RF transmissions, unfortunately the lawnmower is producing quite a lot of it.

Mains cables are not shielded normally that's the whole point. They produce a small localised electric field. Those detectors only work in very close proximity usually within a centimetre of the cable depending.
 

Rambles

Distinguished Member
Sounds like something is wrong with the mower. It might need a filter on it, they are available.

The aerial is doing what it supposed to and picking up RF transmissions, unfortunately the lawnmower is producing quite a lot of it.

Mains cables are not shielded normally that's the whole point. They produce a small localised electric field. Those detectors only work in very close proximity usually within a centimetre of the cable depending.
Thanks, I don't really know him well enough to go and fit a filter on to his lawnmower, nor do I know how to do that, unfortunately.

I'm curious to know why mains cables are not normally shielded. If they are run alongside speaker cables and interconnects, wouldn't some shielding help to minimise any cross interference?
 

Abacus

Banned
Mains just produces a single frequency of 50Hz in the UK, (Interconnects are screened from interference by default, however on long runs a balanced screened cable is best (Hence there used in pro installations like studios)

Mains leads would have to carry a high voltage and current to interfere with speaker cable, so unless you’re in a pro or industrial situation, you can safely forget about it.

BTW. Use any decent quality interconnect for your subwoofer, (One from a pro music store is best, (Avoid the overpriced rubbish produced by HiFi cable manufactures) then run it in parallel with the subwoofer mains cable, and you will find that you will not hear any difference or interference, however, it is best practice to cross mains and low level cables at 90 degree angles to reduce the possibility interference. (To be honest, in a domestic environment your equipment and/or cables would have to be really Naff to cause a problem)

NOTE: Turntable pickup cartridges are the most sensitive to interference, so probably best to separate them.

Hope this helps

Bill
 

ChuckMountain

Distinguished Member
To add to Abacus point, its the 50Hz signal going into the amplifier section that produces the audible hum that sometimes you can get, usually associated with differences in ground rather than picked up interference.

Speaker cables and power cables are not generally shielded as they don't need to be. The voltage involved with the electric fields from mains is not sufficient to produce any noticeable distortion.

Interconnect cables are lower voltage and so more susceptible to interference hence they are shielded.

Shielding cables can introduce its own issues particularly if they are not grounded properly and they can act like aerials and pick up other frequencies.
 

Barcoing Mad

Active Member
The lawn mower is spewing out rubbish in the MHz/GHz frequency range (free space wavelength of a metres). 50Hz has a free space wavelength of 6000 km.

With the former you're worried about picking up interference with dangling bits of wire acting like aerials roughly a metre long. With the latter, you're looking at proximity effects - capacitative coupling (usually f all) or magnetic induction, transformer style. Remember even unshielded leads are laid up as a supply/return pair, so this confines both the electric and magnetic fields.

Biggest pain is earth loop hum - which has driven me up the wall in the past.
 

Rambles

Distinguished Member
Well, curiosity has taken hold, so I have pursued this a little bit more, keeping costs low and scepticism high. I got one of those cheap non contact ac detectors and discovered that two of the mains lead (out of many) in the house are shielded. One came with the Cambridge Audio CXR 200 AVR, and one is currently powering the subwoofer. I can't recall if that power lead came with the subwoofer, or not. Both of these cables seem thicker than the others and have ferrite beads embedded in them.

So, I tried a little experiment, with the amp powered with it's own lead and my CD player powered with the lead from the subwoofer. As much as I hate to say it, there is a difference in sound, the shielded lead sounds better! It isn't a massive change, but I listened to an Elbow album, and Guy's vocals sound clearer and less raspy with the better mains cable, and the instruments have a slightly better separation.

I am aware of confirmation bias and the placebo effect, so I got a family member to do the test blind, making sure they couldn't see which cable was being used, and they said the exact same thing as me!

Not sure what I will do now, I am certainly not spending £40 to £50 on a mains lead, but I have found a site that does DIY kits for £10 to £20 so I may get a couple of them, one for the cd player and one for the HTPC, maybe.
 

Rambles

Distinguished Member

ChuckMountain

Distinguished Member
I am sorry but still going to have disagree with you for a few reasons.

You didn't really do a blind test in the true sense of it and so it was flawed there is stuff out there on proper testing etc but its quite involved and usually quite expensive. You can google it :)

Secondly the pseudo crap science in the first video is utter tosh and the reason you want a shielded cable is to keep stuff out not stop stuff "leaking" out. Its not a hose pipe trying to contain stuff.

I have one shielded cable in my house that I am aware of, due to the fact I cut the plug off it at one point. Its currently in my cables box as I am not sure how to shield it properly...

As I said earlier its entirely up to you and your wallet though :)
 

Rambles

Distinguished Member
Ha, the strange thing is that I totally agree with your opinion, but my ears tell me different!

This house does have weird electrics, I think I will go for a couple of DIY cables for £15 each, even if it is the placebo effect. i might try a trial of the Russ Andrews silencer and Tacima mains conditioner as well. The cost of those aren't that high, so if I hear a little bit of improvement I'll probably think they are worth it. If not, I'll return them.
 

ChuckMountain

Distinguished Member
No your eyes and ears can be fooled that's why you need a proper double blind test.

There is quite a good write up on power cables testing in double blind etc.

There should be no reason why the output wave of the speakers can't be sampled and compared each time. Surely it would be easy for somebody with sufficient funds or interest (a cable manufacturer) to do it. You would be then able to prove differences :)
 

Rambles

Distinguished Member
Yes, I agree. The science and logic makes no sense. On Click this week (BBC News 24) they did a brief story about the guy in Japan who had his own electricity pylon fitted to improve the sound quality on his hi-fi!

I have done lots of research on the internet about how mains power supply affects audio quality, and watched lots of YouTube videos, and I have always been on the side of the sceptics. Although some of the presentations from the other side do seem persuasive.

For me, if it doesn't cost too much and I can hear a little bit of improvement, it seems worth it. I know what you are saying about being fooled / placebo / confirmation bias, we are quite good at critical listening in this house. We recently did the same with acoustic panels, and the outcome was, we don't need them! However with this mains lead issue, there does seem to be something different.
 
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