How To Remove Studio Hum

Paul White - Hello and welcome to this SoundOnSound podcast where we'll be discussing noise problems in the studio caused by electricity, specifically the mains, but also we'll touch upon other subjects as we go. So I'm Paul White and with me is Hugh Robjohns. Hugh Robjohns - Hello there. PW - First of all Hugh, we can't all afford to have bespoke studio wiring, so if you've got a home studio with a standard ring main in it, what's the best way to arrange your plug boards so that you minimise the risk of earth loops? HR - I think ring mains are actually a bit unique to the UK, aren't they? PW - Possibly so. HR - I think the general issue is that you want to try and arrange your mains distribution as a star feed from ideally a single socket or a dual outlet socket, but one point on the mains distribution in your building, so that everything is basically funneling its ground return current back into one place because that avoids or at least it minimizes the risk of ground loops. PW - So if you need a dozen sockets, you would plug maybe a four way extension into the main socket and then plug another extension lead into each of those four sockets. HR - Exactly that. So you've got this kind of star arrangement. So the worst thing you can probably do is arrange your plug boards in a kind of daisy chain where you have one plug board plugged into the wall socket and then another plug board plugged into that first one and then another board plugged into that one and so you've got this daisy chain of plug boards because if you've got leakage currents in the earth line from the thing plugged into the very most distant plug board, it has to work its way through all the others and it basically, because each of the cables has some resistance, any current that flows down through that long line builds up a voltage, and that voltage is what causes the ground loop problem. So by doing this kind of star arrangement, you minimise the risk of those currents adding up. PW - And it's the same problem if you plug into two different power outlets at opposite sides of the room, I guess. HR - It's the same, same basic problem, because again, You've got two sockets with a lot of wire in between them. A lot of wire has a small resistance, a small resistance with a small current produces a small voltage and we only need a small voltage to create an audible hum. So we want to try and avoid that wherever you can. PW - Okay. Do you want to talk a little bit about uninterruptible power supplies because apart from being uninterruptible, they can also clean your mains to some extent, I believe. HR - Some of them can, yeah. I mean it varies a bit with different makes and manufacturers, but some of them will certainly do a lot of the things that those power conditioners will do by default, but the nice thing is some of the online ones actually completely regenerate the mains supply. So they generate a perfectly sinusoidal mains waveform, whereas the stuff that comes out of your wall socket might have spikes and transients and dips caused by other people using electricity elsewhere on your estate or industrial estate or wherever you happen to be. PW - Yeah, one problem I've come across. I was playing a gig some years ago. I got a guitar with supposedly noiseless, stacked humbucking pickups and it was picking up a lot of interference and when I got back home and checked it, the problem was corrosion on the jack sockets which was leading to a high resistance ground path. I mean, is this something you've come across, Hugh? HR - Yeah, I have and it's not just on audio connectors, although that can certainly be an issue, but also on mains plugs. Actually, if you get, you know, a tarnished earth pin on a mains plug, it does the same problem, it causes a high resistance earth path. The more resistance you've got, the more voltage develops. So it's worth keeping those plugs clean. PW - It is. I remember a lot of people taking the mickey out of Martin Walker when he used to get wire wool to clean the earth pin on his mains plugs, but it's a perfectly good thing to do. HR - It is, actually. I think Martin used to do it as a sort of ritual of his sort of once a year, where he'd unplug absolutely everything in his studio, clean up all the brass plugs on the, you know, the earth pins on the mains plugs and actually the live and neutral pins as well to keep them all clean. You could use something like Deoxit, which will extend the time it takes to retarnish and just keep everything nice and clean and low resistance. It does make a difference. PW - Yeah, that Deoxit D5 is magical stuff, isn't it? HR - It is, yes. PW - Okay. We've spoken about. Ground loop problems, but there are also groundless problems, if you like. We've come across this in laptop based studios where absolutely nothing is grounded. HR - Yeah, it's very true. I wrote an article for the magazine not that long ago about grounding problems, and somebody said, you see it on the forum, a lot of people come on and say, I think I've got a grounding problem. And they're almost always right, but it can be because you've got too many ground paths, which is the ground loop issue, or it can be that you don't have enough, which is the thing you've just talked about, where you have a laptop system that doesn't have a ground at all. Increasingly, these days, equipment is made in a format that's called double insulated or class two, where the mains lead only has the two connections. It's the sort of figure of eight type mains plugs often. And there is no ground connection in there at all and that means that everything is kind of floating around. And if it's floating around, all of the equipment can act as an aerial and pick up whatever kind of electromagnetic interference happens to be floating around in your studio. PW - Okay, one simple way around that that I've found is to make up a very short lead with a floating jack socket at one end and a jack plug at the other end. And then you take the ground from the jack socket via a long piece of wire to a grounding plug. And then you just put that in series with your guitar lead or your instrument lead and that seems to do the job. HR - Yeah, that would do it. I mean, I've used leads with crock clips on the end and clip one end on something earthy on the interface and the other end on something earthy in the room, maybe a radiator pipe or the screw connection on a main socket. Anything like that which, you know, is definitely grounded properly and just all the noise goes away. Basically what happens is the equipment is built inside a metal case, or if it's a plastic case, it's often got a kind of metallised layer on the inside, which is supposed to act as a Faraday cage. And the idea of a Faraday cage is that it's a conductive enclosure that stops electromagnetic interference from getting in. But if it's not actually grounded, it doesn't work that well. I mean, there are situations where you don't need to ground it, but generally they work better if you do and it can make a huge difference to the background noise of your system. PW - And it is worth mentioning special grounding plugs, because it can be dangerous just to put a single ground wire into a normal mains plug and then plug that in the mains, because if someone trips over it and pulls it out, it could touch one of the positive terminals on the way out, which would not be good news. HR - Yeah, it could. I mean, it's unlikely, but it certainly could happen. It's not worth the risk. You can buy proper grounding plugs. There's a company called Groundology that do them and, you know, they're not the cheapest things, but they're very well made and they're very reliable. The thing to watch out for is if you go on Amazon or somewhere and try and find a grounding plug. Often the ones you find there are designed for electrostatic protection and they have a big resistor built in to limit the flow of current, which is great from a safety point of view if you're putting a strap onto your wrist to stop your getting electrostatic shocks when you're working on, you know, delicate electronics or something. But it doesn't help in the case of an interface, it doesn't have a ground because, it still doesn't have a ground, it’s got this sort of 1 meg resistor in the way and it won't actually help. Make sure you get the right kind of grounding plug. PW - Yeah, so what it looks like is a regular plug, but the live and neutral pins are made of plastic and the ground pin is still metal, yeah? HR - Yes, yeah, but just make sure it doesn't have the resistor in it. It'll be written in the advertising blurb whether it does or not. As I say, Groundology is a good supplier of appropriate plugs for this application. PW - Yeah another time that people blame the electrics for noise is actually to do with radiation from computers. I mean, I know that if you sit close to a laptop-based system and you have an electric guitar on your lap, you're likely to get a lot of strange digital interference and all that goes away if you move a couple of meters back from the computer. HR - Yeah, it does. I mean, in a perfect world, nothing should radiate interference and we have, you know, the CE regulations and so on and similar regulations in other parts of the world that are supposed to stop equipment from radiating interference or being bothered by radiated interference. But unfortunately, a guitar is pretty much the perfect aerial to pick up any kind of interference and because the signal levels are so small, it doesn't take much to cause problems. So yeah, keep away from computers, keep away from anything digital, CD players, digital radios, anything like that. PW - Or anything with a big transformer in it. HR - Anything with a big mains transformer because of course the pickup coils in a guitar are sensitive to magnetic variations and a main transformer produces a magnetic field. So yeah, keep well away from that. We did a studio SOS a while back, you probably remember where they had a very long cable for a… PW - It was for a mic pre-amp I think. HR - It was a mic pre-amp. They had a very long cable in a multi-core that was feeding a mic preamp at one end and all the mics in their studio at the other and it was too long for their room, basically. So they coiled it up in a very neat coil behind the desk and then inadvertently, just threw a mains plug board with a couple of plug in wall wart-type mains transformers on the top, sitting right on top of this coil of cable and wondered why all the microphones were hummy. PW - Screened cable can only do so much. HR - It can only do so much. We didn't have to move the plug board very far to cure the problem, but yeah, sitting transformers on top of audio cables, not a good idea. PW - Also, I believe that some poor quality external power supplies can put noise back onto the mains. HR - Yeah they can, it has been known. So again, try and get decent quality power supplies. PW - Yeah, I think if you're going to be using pedal-style effects and anything that needs the typical 9V supply, it is worth buying a good quality, isolated output regulated supply, rather than using the little bricks that come with the pedals. HR - Yeah, I mean, it's neater as well, isn't it? You can keep all your power supplies in one place. You've got to be a little bit careful when choosing these isolated supplies, because some are more isolated than others, aren't they? PW - I was about to mention that. Some of the cheap ones that you find on eBay for about maybe £30 or $30 or whatever, it says isolated and what they have is they have a separate regulator for each of the outputs, but they still have a common ground. And that can cause all kinds of problems, especially if you have one of those pedals that needs an opposite polarity because with a properly isolated supply, you just have a crossover lead to flip the polarity and you might have a positive center pin instead of a negative center pin and it works. But if you try to do that with one that's got a common ground, it's not going to work. HR - Yeah, absolutely. So really, those kind of supplies are buffered rather than isolated, aren't they? PW - Yeah, they're not truly isolated at all. They're just individually regulated, I think is probably the correct term. So you need to spend probably a couple of hundred pounds on a really good isolated power supply. HR - The other problem you can have sometimes is with digital effects pedals. Because they're digital, they put quite a lot of noise into the power supply rails and if the power supply is not properly isolated, that noise can then get back out into the power supply that goes to all the other pedals, so you end up with digital noise on your analogue pedals. PW - Yeah, which is a good reason not to use a single power supply with a daisy chain connector on it. Especially if you have low current analogue pedals, as you say, sharing with digital pedals, they will tend to pick up quite a lot of noise. I know that power supplies are not very exciting, they don't make an exciting noise, but that's the whole point, it's an exciting noise that you can live without. HR - Yeah, it's one of those annoying things because you kind of assume that your power supply is just there, it's a utility. But actually, the way you configure the power supply in your room and the way you connect to it, the different kinds of power supplies you plug into it can all make a difference and it doesn't take much to cause a problem that can be really quite hard to track down. PW - So talking of tracking down, if we have a hum or a buzz problem, what's your normal procedure for trying to track that down? HR - I think the first thing I do is unplug everything and then plug things back in one by one, starting with the most critical elements. So your computer, in a studio situation is probably going to be your computer and your interface, they're the first two things to plug in. Listen on headphones, make sure they sound clean or not. PW - Then add your monitors. HR - Then add your monitors, make sure they're clean or not. Often you do find a problem because if you have maybe a desktop type computer, that will be grounded through its mains lead. Laptops generally not, but desktop machines generally are and then if you plug in your active loudspeakers, they're probably grounded. So immediately, you've now got two mains earth connections, one through the speakers and one through the computer and consequently, if you've got two connections like that, you have the potential for a loop. Now, if you're using balanced audio connections, that loop shouldn't matter because the ground path that runs from the first mains socket into the computer, into the interface, across the audio cables to your loudspeakers, back to the main socket, that loop doesn't carry any audio and the audio circuitry should be kept clear of that ground path. So it shouldn't be a problem with balanced leads. Unbalanced leads, of course, the audio path runs along the ground side of the shield of the cable, so it is a problem. But with balanced leads, you shouldn't have a problem, but sometimes you do because of the way manufacturers design and build their equipment. PW - So we should explain ground lift switches at this point, I think. HR - That was the next thing to come onto, is how you break that that path the ground path and obviously you can't break the ground path in either of the mains leads because the ground is there for safety, so the only place you can sensibly break it - well, there's two places. One is in the shielding of the audio cable between the interface and the speakers and the other place is in the shielding on the USB connection, assuming it's USB between your interface and computer. Now the USB thing used to be a big problem, because although there were ground breakers for USB, they didn't work at USB2 speeds, they only worked at USB1 speeds and that could cause a problem, obviously, with your interface not running properly. You can now get very well designed USB2 ground breakers and they do work quite well. But most people would choose to break the ground in the audio cables because that's cheaper and easier and just simpler to do. Some loudspeakers will have a ground loop switch on the back and what the ground loop switch does is it separates the cable screen ground from the main's earth ground, physically disconnects them. Sometimes it'll put a resistor in the way just to stop the ground currents flowing. There are different ways of doing it, but that's a very simple option. Some speakers have them, some don't. If they don't, you have to break that ground path yourself. Now you can either open up the XLR connectors or the jack connectors and physically snip out the screen with your snippers. PW - Just at the one end. HR - Just at one end, generally best to do it at the destination end, so at the speaker end. Or you can use something else that will break the ground and the easiest way to do that is to use something like a line isolation transformer box, because transformers pass the signal through a magnetic coupling, not a direct electrical coupling, so the grounds are kept separate through the transformer. PW - Of course, unless you've got a really good transformer it could affect the sound, so it's probably better to do the cable trick. HR - The cable trick is certainly the easier and sonically better idea. PW - And cheaper. HR - And cheaper for your Yorkshire man. I often recommend using, there's a company called ART or Art and they make a couple of line isolation transformers. There's one called the clean box two and there's one called the DTI. Inside they're essentially the same, but the DTI box has all sorts of connectors on it, which makes it a very useful box for just testing and fixing things. So I like to use those and the quality of the transformers in those is pretty good. You'd need a very good monitoring system to hear a problem going through there, but it's an easy way of just plug it in quickly. Has it cured the problem? Yes. In which case you can decide whether to get better transformers or just get the snippers out and snip the cable. PW - Okay and then after that, you start to plug in your patch bays or whatever other equipment you have, your hardware outboard and go through the same routine with those. HR - Absolutely and you just have to do it one-by-one and if you hear a problem, solve it, move on to the next one. Often you'll keep plugging things in and there won't be any problems with hums at all and then suddenly you'll find something you plug in and it causes all sorts of issues. But you have to go through it in that kind of piecemeal process to identify each piece, cure any problems that they introduce, move on to the next one. PW - Yes. Frustrating, but necessary. HR - Absolutely. And if you change the studio, rewire something, you just think oh well, I don't want that box in that bay over there, I’ll go and put it in a rack over there instead and you've got all sorts of problems again, so you've got to go right back to the beginning and work through and find out what you've done that's caused that ground loop to appear, or whatever. PW - Yeah but as you say, if you're lucky, none of that will happen, because your equipment will have been designed perfectly and as long as you use balanced leads, it's all going to behave nicely. HR - Absolutely, yeah. PW - Okay, well I think that's about all for this one, so it's goodbye from me, and it's goodbye from Hugh. HR - Goodbye, thanks for listening. Sam Inglis - Thank you for listening and be sure to check out the show notes page for this episode, where you'll find further information, along with web links and details of all the other episodes. And just before you go, let me point you to the SoundOnSound. com/podcast website page, where you can explore what's playing on our other channels.