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Clean Earth sockets

IronFreely
I’m just wondering about how clean earth sockets (Some of you may call these high integrity sockets) fit into the requirements of BS7671 in terms of their use in domestic homes.


One of my clients has asked me to look into the use of some clean earth sockets to be used to power audio equipment in their home studio, the basic idea is that a completely separate Earth helps eliminate what’s known as an earth hum on audio equipment caused by functional earth leakage of other equipment connected to the same circuit and disturbances originating from the suppliers earthing arrangement. The basic concept seems to be to insulate the cpc from the earth terminal of the socket outlet which then has its own independent Earth electrode, high integrity sockets seem designed to accept and insulate a cpc and a separate earth. 


My concern is that this sort of thing is usually used in a restricted access environment where only IT or audio engineers are going to be around and might be considered trained and competent to understand the risk of introducing an earth potential to the equipotential zone that is not in itself connected to the equipotential bonding. It wouldn’t be a problem if I could guarantee restricted access or that the socket would only supply class 2 equipment, but as this is a home studio it seems a bad idea to have an earthed metal casing of some piece of audio equipment that may be completely separate from all other earthing and bonding in the property? 


id appreciate your thoughts and advice please, I’m confident a separate clean earth will resolve the earth hum problem which I’ve seen work well in theatres (essentially restricted access) before but never in a domestic property.


Edit: I should add that the property is a TT property but because the street is a hodgepodge of TNS and TNCS (I have other neighbouring clients really close by) you should assume the gas and water pipe are throwing in a bit of PME related disturbance.
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    Well if musicns could learn to sing/play at an audible level then such hums, hisses, clicks and such would be redundant along with all the amplifiers
  • 0
    In a home studio it can be difficult to eliminate all sources of noise which affect audio signals. The OP can hear mains hum, and eliminating it can be difficult, as gkenyon‍ has pointed out. The difference between a 'clean' source and one that is noisy is often subtle, but you know it when you hear it and it isn't about measurements of signal to noise ratio or the like at all.


    Balanced inputs (where there are two signal leads, one a send and the other a return, with a separate screen connection) are less prone to such problems, but unbalanced inputs (single signal send and common screen/signal return) from guitars and other instruments can be a problem. Signal levels from mics and guitar pickups are very low (in the mV range) so even what might be thought of as very low induced hum levels will be decidedly audible and very distracting, and potentially ruining from a recording point of view. As the OP has said, he doesn't have to measure it as he can hear it directly.


    There are articles dating back a long time on the abolition of ground loop effects - for instance http://www.muzines.co.uk/articles/studio-earthing-techniques/4139


    My brother has a home studio, and I maintain the equipment he uses. In one case he recorded a number of lead vocals using a brand-new balanced mic cable which unknown to him was defective leading to a very low level of background hiss, occasional clicks and distortions on the recordings. No amount of 'masking' by overlaying the instruments in the mix could overcome the defects in the vocals he recorded with the duff lead,  which he had to redo once the duff lead was replaced.


    Good luck in eliminating the problem.
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    It seems as though every electric guitarist with a valve amp (which absolutely must be used as their monitor) will have a sixth sense for finding a power source on stage thats shared with something motorised. You do your best to give noise just the one circuit (heck if neutrals didn’t get a bit melty we’d give em their own phase) but guitarists want to plug their hairdryer in using six extensions from the cleanest power you’ve got on stage, or they’ve brought a fan and a smoke machine that they’ve got lined up on a four gang with their amp and a power drill so they can at least look good while their buzzing valves destroy my perfect mix.


    might have got a bit carried away with there.


    p.s. all really awesome guitarists tour with a power drill, fact.
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    Chris Pearson:
    IronFreely:

    Thanks, this is the kind of advice that makes this forum a real gold mine, you just have to sift through the occasional troll suggesting the only issue is tinnitus! 


    That's not very polite!


    I return to the question about the amplitude of this noise. Has it been measured; and if so, is it at a level which is capable of being perceived? If either answer is "no" then any attempt to abolish the noise may be a waste of time and money.


    ETA: we are talking about a "domestic home" are we not?




    We are talking about a home studio, not what you might term an audiophile's "snake oil".


    Analogue interconnections that are used in some recording setups can be a minefield for very audible "hum", and it's sensible to have at least a structured approach to the mains. The same issues can plague live performance venues too.


    It is this particular "hum" which got me thinking about how I've resolved it in the past ... and then the "balanced output" consideration to help reduce the impact of the actual mains wiring by changing it from "common mode" to "differential mode".


    If there are any electric guitars in there, you do need to take care - especially with single-coil pickups - as any electric guitarist will tell you. Electric guitars need to be earthed to prevent "cracks" and "pops" that can happen when you touch (or let go of) the strings, but this makes them effectively "common mode" - so "common mode" single-phase mains hum can be difficult to eliminate.

     


  • 0
    3000 watts (peak more like 2kW average) of 240 v isolation at a price point  that may be worthwhile for a test.  Of course it is sod all use against magnetic induction, but will break any CPC gradient problems.   Try and get all the audio gear on one radial.

    Neither side of the secondary is earthed, and the lid unsrews so you can  decide if you want to carry the primary CPC on  to the secondary or use your own earthing method for the output side.


    If it works,  versions for deeper pockets /longer arms  are then available


    Inrush when turning on large transformers can be a thing. A series resistor in the phase (s) comin in and shorted out after 50msec or so once the core has at least partly magnetised can help keep the breakers in
  • 0
    Chris Pearson:
    IronFreely:

    Thanks, this is the kind of advice that makes this forum a real gold mine, you just have to sift through the occasional troll suggesting the only issue is tinnitus! 


    That's not very polite!


    I return to the question about the amplitude of this noise. Has it been measured; and if so, is it at a level which is capable of being perceived? If either answer is "no" then any attempt to abolish the noise may be a waste of time and money.




    You’re right, that’s not very nice because derailing someone’s query by suggesting its more likely the OP has tinnitus because they haven’t measured a noise to prove they can really hear it is about as usefull as suggesting you should measure ambient light levels to prove the picture you can see on your bedroom wall isn’t a hallucination. Chris I’m sure they have an earth hum, I can hear it, the client can hear it, the clients band mates can hear it, we can all hear it when the equipment is on, we can all tell it goes away when the equipment is off, we can all hear it on recordings made with this equipment, we can hear it has been significantly reduced when plugged into the power supply in my shed which is a TT island, a group of people with something like 300 years of collective experience in music and sound engineering do not need to measure a sound to know they can hear it nor do they need to measure it’s absence to know it’s been eliminated by driving across town and plugging it in elsewhere. The question is NOT IF there is an earth hum, there is, the question is how to reduce or eliminate it within the scope of BS7671 in the location they want to use it. If you don’t like the picture you take it away, you don’t need to prove you can really see it first. In any case amplitude on equipment of this nature is a variable not a constant, measuring it is subjective to controllable gains with the exception of the powered monitors which present with all faders nulled. Chris please if you can’t help with solving the problem please go away and stop suggesting we’re imagining it, it comes across as patronising and rude. Thank you. 


  • 0
    IronFreely:

    Thanks, this is the kind of advice that makes this forum a real gold mine, you just have to sift through the occasional troll suggesting the only issue is tinnitus! 


    That's not very polite!


    I return to the question about the amplitude of this noise. Has it been measured; and if so, is it at a level which is capable of being perceived? If either answer is "no" then any attempt to abolish the noise may be a waste of time and money.


    ETA: we are talking about a "domestic home" are we not?


  • 0
    Whilst DP switched socket-outlets would be preferable, as I don't see them as being necessary, because the isolation in a socket-outlet is removing the plug, which is double-pole.

    The 2-pole isolation requirement is there for TT as well,, and we can use SP switched socket-outlets for that can't we?


    HOWEVER, a guitarist who opens up their own amp, say to change valves, might assume (erroneously) that the switch provides isolation, so even leaving it TT I might be inclined to consider DP switched socket-outlets?


    Apologies, no handy recommendation for the transformer, but I guess if you posted what your power requirement is, someone on the Forum will have a recommendation for you from jobs they have done in the past.
  • 0
    This is a chuffing good idea! Now that I think about it I’ve seen similar set ups in venues before, a plug and play power conditioner is essentially a 240/240 isolating transformer.

    Ive got two questions if I may? Firstly, presumably suitable double pole isolation can come in the form of a bog standard BSEN 61008 RCD, or are you suggesting that DP socket outlets should be used additionally.

    Secondly can you recommend such a transformer of this nature? I’ve never installed one and the only ones I know of are the sort used in medical locations....


    Thanks, this is the kind of advice that makes this forum a real gold mine, you just have to sift through the occasional troll suggesting the only issue is tinnitus!
  • 0
    If the pockets are deep, and assuming single-phase installation, I thought of an isolating transformer to provide a local TN-S system for the studio.


    However, better for reducing "hum" would be an isolating transformer with a 115-0-115 centre-tapped secondary. Earth the centre-tap, and this Earth can be bonded to the TT earthing system. If < 10 kVA you might get away with 20 Ohm to 200 Ohm for the earth electrode resistance. If greater than 10 kVA, additional electrodes recommended to get the earthing resistance down to 20 Ohm.


    Even though the secondary is TN-S, because it's centre-tapped earth, protective devices and means of isolation for on all circuits will require disconnection of all live conductors.


    Why is this a good idea?
    1. Provides effective isolation from protective conductor currents elsewhere in the installation

    • Protective conductor currents from all mains noise filters in the studio will be effectively zero.

    • A "balanced" supply is better for noise reduction than a "single-ended" one.

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