When setting up a studio, the temptation is to make do with the existing wiring – but this can lead to problems with hum and interference, as Paul White explains. This article is the first in a two‑part series.
When you're setting up a serious home studio, one of your first considerations should be the electricity supply. While simply plugging into the nearest 13A socket and hoping for the best might be OK for the bedroom recordist, it does run the risk of electrical interference from other systems in the house. Equally important is the fact that even a modest studio installation may require literally dozens of mains plugs, and trying to shoe‑horn all these into one wall‑socket, using domestic distribution boards or adaptors, is simply asking for trouble. Even if the total load on the socket doesn't exceed the stipulated 13A, using a mixture of cheap distribution boards and adaptors risks intermittent mains connections, which can arc, causing interference. If you're wondering why this should be, try looking inside a typical plastic distribution board and you'll see that the sockets are actually small pieces of metal crimped onto rigid wire bus bars; once you've used them a few times, the sockets lose their spring and fail to make good contact with the plug. And because these faults are likely to be intermittent, any resulting interference may take a lot of tracking down. So, what's the right way to do it?
Spur Or Ring Main?
I should say at the outset that the main cause of concern is not overloading of the mains circuit, but interference and mains hum caused by inappropriate wiring. Most pieces of studio equipment take relatively little current and the needs of a typical home studio can often be supplied by just one or two 13A sockets — provided that the means of connecting to those sockets is sound. Modern houses use a form of wiring known as a ring main, where the main electrical cabling forms a complete loop which starts and finishes at the fuse box. Wall sockets are then positioned anywhere on the loop. Ring mains can cause problems with induced hum, and though most people get away without too many problems, a properly‑designed spur system is less likely to lead to hum and interference problems. If you must use a ring main, it's better if it doesn't make a complete circuit of the room; working inside a complete loop of live mains cable (which is what a ring main is) increases the risk of induced hum. If in doubt, get an electrician to check your wiring and have it modified if at all possible.
If you're planning a new mains wiring system, you should specifiy a separate consumer unit for your studio area — and in a larger facility, fit two, one for the 'clean' audio/computer supply and a second for 'dirty' power, such as heating, lighting, coffee machines and so on. A consumer unit is the modern equivalent of a fuse box, but is more likely to be equipped with resettable switches which turn off in the event of excess current, or if mains current leaks into the earth conductor — as may be the case when a piece of equipment develops a fault. These trips are known as RCBs, or Residual Current Breakers, and should always be used in preference to the old‑fashioned fuse. Not only are they more convenient to reset, they could well save a life, as a human being strung between the live cable and anything that's earthed counts as a fault condition!
Interference
Using a separate consumer unit which is fed from the building's main fuse box also provides a degree of natural interference rejection, helping to minimise clicks and buzzes caused by the likes of fridge thermostats and central heating systems. If these continue to break through onto your audio, engage an electrician to fit suppressors to the offending items.
Unless you know exactly what you're doing, you should have the supply put in by a qualified electrician, as there are certain safeguards required for spur systems that don't apply to normal ring mains. In a spur system, every mains socket is connected back to the consumer unit by a single length of cable, and each spur should be separately protected by a fuse of circuit breaker. Even though studio equipment takes relatively little current, the lower the impedance of the wiring, the better. Translated into practical terms, this means using the heaviest wire practical, and though the electrician might find your request for 30A cooker cable throughout a little odd, it won't add that much to the price and it will help keep down interference from outside. It will also help prevent the sound quality suffering, as it might when the mains supply to one piece of gear is modulated by the mains current taken by current‑hungry equipment such as power amplifiers.
Hum
To minimise the risk of ground loops and radiated hum, all the mains cables should be run together as far as is possible; it helps if they can be run around the top of the room with drops to the various sockets. The logic behind this is that it keeps the mains as far as possible from your signal cables, which reduces the risk of hum pickup. Some benefit may be obtained from running the cable in metal rather than plastic conduit and ensuring that the conduit is earthed. While you're at it, get the electrician to check the earthing spike which forms the contact between your mains earth and the planet below. If it isn't providing a suitably low impedance path, consider getting a longer one banged in. Figure 1 shows how a typical ring main is set out; Figure 2 shows a suitable spur system for studio use.
Distribution
Always plan for as many wall sockets as you can in your studio, but also be prepared for the fact that you won't have enough! To reduce the risk of hum‑causing ground loops, all the audio equipment should, if possible, be plugged into the same socket or pair of sockets, though a spur system is more forgiving in this respect than a ring main. If you're not sure about the power consumed by all your equipment, power ratings are normally quoted in the user handbooks or marked on the back of equipment cases Add all these together and ensure that you're not connecting more than 3kW to any individual socket. Unless you run a studio with a PA‑sized monitoring system, you're unlikely even to come close to this figure; most home studios take well under 1kW.
Lighting and heating tends to take much more power than the audio equipment and should, ideally, be run from a separate 'dirty' circuit, as mentioned earlier. In any event, it must not be plugged into the same spur as the audio equipment.
In order to split the power from a pair of 13A sockets to drive the studio gear, it is best to make up a distribution board using commercial‑grade, metal‑cased, switched mains sockets. These may be screwed to a suitably solid piece of wood and then wired, spur‑wise, to a heavy‑duty junction box using 2.5mm twin and earth house wiring cable. The junction box then terminates in a trailing mains lead made from the heaviest flexible cable that you can fit into a 13A plug. For a typical studio load, 15A cable is more than adequate for this application, but keep the lengths as short as possible and never coil unused mains cable, especially if it is passing a lot of current — it has been known to melt!
Figure 3 shows a practical distribution board. In my own studio, I use two such distribution systems, one to feed the MIDI rack and one to feed the mixer/monitor/recorder/effects department. If you mount the distribution boards in the back of your equipment racks, the amount of exposed cabling can be kept to a minimum.
Computers should be fed from a different spur to the audio, but shouldn't be fed from a 'dirty' supply because of the risk of crashes. A proprietary computer mains filter is a wise investment; though the protection they provide is limited, they help filter out mains spikes and surges.
Finally
It isn't enough to have a good mains supply — you must also check your equipment to make sure that the plugs are properly wired and that the correct ratings of fuse are fitted. This sounds obvious, but it always amazes me how the wires in plugs manage to work loose, even when they've not been moved! Aside from being dangerous, loose wires are liable to arc and cause interference. Check your plugs carefully, ensure that the cable grip is clamped firmly on the outer sleeve of the cable, and while you're checking the fuse rating, make sure the fuse‑holder grips the fuse tightly. If it doesn't, pinch it in a little using pliers. Also ensure that the fuse‑holders on the back of your various pieces of equipment are reasonably tight. Finally, though it's tempting to remove the earth lead from certain pieces of equipment as a quick cure for hum caused by ground loops, it is potentially dangerous — the earth wire is there for your protection in case something else fails. In a correctly‑designed system, you should be able to cure any ground loop problem by modifying your signal leads, not your mains leads — and that's something I'll be tackling in a future article.
"Always plan for as many wall sockets as you can in your studio, but also be prepared for the fact that you won't have enough!"