GROUND LOOPS, SNAPS ,CRACKLES and POPS!! by Michael Gore copyright 1994 I've been an Audio Technician since 1972 when I worked in =20 major recording studios (CBS Records, Fantasy Records) and=20 since going independent as an Audio Tech in 1982 I've set up=20 loads of small, intermediate, and large studios. There are=20 more than a few things I've learned over the years, but one=20 of the most important is How to Troubleshoot a system, what=20 to look for, some basic tests even the non-technical can do=20 for themselves. And with just a simple approach to trouble- shooting your own system, you'll be able to save money by=20 fixing the problem yourself, or at least you'll know when=20 to call in outside help. In this article I'm going to try=20 and give you an approach to troubleshooting your own studio=20 that will isolate the faulty component or equipment. =20 First off, one of the most important things to know is what a=20 professional studio control room should sound like, because that's=20 your goal: to sound as good as you can. What comes out of any top=20 studio's monitor speakers, is well, nothing... that is when there's=20 no music, there is no noise. This seems obvious, but time and time=20 again I go into project studios where there are buzzes and small=20 audible pops and loads of hiss and hums coming out of the monitors.=20 And too often the person who runs the place thinks these sounds are=20 "normal", and that they have to just live with them.... NOT SO!! If you've set your system up correctly, you should be able to turn=20 your monitors up to a comfortable listing level, and hear no hiss,=20 no hums and a good clean nothing. If you turn your system way way up,=20 all you should hear is a nice clean hiss way in the background, with=20 no hums, no squeals no buzzes. Getting here, to the quiet studio, isn't hard. This is how you begin=20 to trace those buzzes, hums and noise, and to eliminate them if = possible... First off, you've got to have a quiet power amp, and luckily almost=20 all of them are very quiet thesedays. You can test this yourself, by = first=20 turning OFF the amp, then removing the Input connections, then turning = the=20 amp back ON, and slowly turning up the volume. All you should hear is = hiss,=20 and this you should only hear when the amp is turned way up. If you = hear=20 Buzzes, pops or your local radio station, try turning OFF the amp then=20 installing shorted Input connectors (that is the connector's "Hot" and=20 "Ground" points are connected together (shorted)... so there is no = possible=20 Input Signal). If you don't hear a nice clean hiss, them you have a bad = Power amp, so go get it fixed. So now you've got a clean Power Amp. It's quiet. The next thing is=20 to turn it OFF and hook up the output from your console, then turn it On = and=20 slowly bring up the levels on the Power Amp to reasonable volume: have = the=20 Monitor Output and all the faders of the console down, and all the = channels OFF. =20 Again it should be just about as quiet as the Power amp alone( a little = more=20 hiss is to be expected, but it shouldn't be much). Then bring up the = console's=20 Monitor level control to "normal" (which in almost all boards is about 2 = o'clock=20 or 3/4 of the way up). The system still should be quiet, no hums, no = clicks,=20 no buzzes. =20 OK, so you don't have a quiet system, what should you do? Note that=20 when I wanted you to check out your Power Amp, we ISOLATED it from any = other=20 cause of noise. We listened only to it, nothing else. We made sure = that not=20 even the wires of the Input cords were connected, since those wires = themselves=20 could have caused a "Ground Loop", which would have caused hum in our = system. =20 With a few slight modifications, we need to do this every step of the = way,=20 isolate pieces of the system, and determine what pieces are causing hum = or=20 buzzes, and what are clean. So say that when the console is connected to the power amp, you have=20 a hum, even when you turn down the console's Monitor output. This is = most=20 likely a Ground Loop, which means that there is more than one ground = (which=20 is your system's "Zero Volt" reference). Once there is more than one = system=20 ground, if there is even a very, very tiny difference in Voltage = between them,=20 that small difference will be amplified just as if it were any other = normal=20 audio signal. After all, the heart of the matter is that you want all = signals=20 "Not equal to Zero Volts" to be amplified! So one piece of gear's Zero = had=20 better exactly match each and every other Zero in your entire system. = If it=20 doesn't, that difference ends up as a 60 hertz hum or buzz. So next we'll have to determine if the console, by itself,=20 is quiet. And just as we did with the Power Amp, we'll have to isolate=20 the console from all other systems, except for the Power Amp. So you=20 have to disconnect each and every piece of gear plugged into the = console. =20 Out go all those Synth connectors, reverb and effect connectors, what=20 you want is nothing connected to your console except the Power Amp.=20 Yes you'll need to dis-connect everything. Once you've done this,=20 and all cables and connectors are removed from the console (except=20 the feeds to your Power Amp), you should have a quiet system once again. = =20 If you don't, try running a Ground wire (12 gauge Green multi-strand=20 wire... you can get this at any home improvement hardware store) from=20 the Chassis of the console to the Chassis of the Power amp. Strip off=20 1/2 inch of the outer cover on both ends so bare wire is exposed, and=20 find a screw on the console to temporarily hold one end of the wire,=20 then holding the cover of the wire, touch the chassis of the Power Amp=20 (don't have the volume up very high!) This will either bring up the=20 hum (so you don't want the wire connected at all) or it will bring=20 down the Hum (then you'll want to crimp "Spade Lugs" on the ends of=20 the wire, and find a screw you can use to clamp each end tightly to=20 each chassis, never never just wrap the bare end wire around a screw=20 and leave it that way! Always use Spade Lugs: first you Crimp and=20 then Solder... ask at the hardware store if you don't know how to=20 crimp a Spade Lug... it's easy, and you already know how to solder a = wire)=20 =20 If you've still got a hum, make sure that the connectors are wired=20 correctly. Finally, if nothing helps, you'll need to try installing a=20 pair of good quality audio transformers between the console and the = Power=20 amp. A transformer will Isolate the equipment from each other (no = ground=20 wire between them), and thus there cannot be a ground loop. If you've=20 still a hum, even after installing a transformer between the Console's=20 Monitor Output and the Power Amp's input, well then the odds are pretty=20 high that the console itself is causing the hum. =20 Usually that mean's the Console's Power Supply is faulty, and isn't=20 putting out clean DC voltages, or that the Console itself is somehow=20 picking up a massive magnetic field nearby, or there might be an = internal=20 chip that's gone bad... I had one client who called me after he built=20 and did his own wiring of his studio, complaining of a hum in the = system. =20 I did ALL of the above, and after testing the Console's Power Supply,=20 I could only surmise that there was a magnetic field of some very large=20 strength nearby. Then I physically turned the console 90 degrees to the = side, and Volia! the hum went away. It turned out that there were the=20 main AC supply cables to 2 TV stations running exactly parallel to and=20 at the same height my client had placed his console (it was a basement=20 studio in an old office building). The console's ground buss (the Zero=20 reference wire) running the length of the console was too thin, and the=20 ground connections inside the console were not solid, and they allowed=20 a bit of induced hum into the system. Turning the console would work or = redoing the internal grounding of the console would work. =20 Now if bringing up faders on your console brings up a hum, you're=20 better off, since you can just bring up each fader until you find the=20 culprit, then remove all cables to and from that one piece of gear. =20 If the system returns to a quiet state, then you'll need to try a ground = wire as we discussed above, once you re-connect the offending piece of=20 equipment back to the console. Next you'll have to try and use a = transformer,=20 to make sure that the gear is working OK, and there is indeed a = grounding=20 problem. And remember, you need to TOTALLY ISOLATE it, you can't just=20 isolate the Outputs and leave the Inputs connected, grounds are in both=20 Inputs and Outputs, and even in MIDI connectors too! You have to=20 disconnect every connection, then you can try a transformer on just=20 the Output cables to the console. If the gear is now quiet, try=20 connecting the Output directly into the Console. If it now hums,=20 then try the Ground Wire. If it still hums, but didn't when the=20 transformer was used, then check your audio connectors, you might=20 have mis-wired something. If all else fails, then you'll have to=20 get transformers for this piece of gear. One thing to try is to=20 physically move remove the piece of gear causing the hum from any=20 rack system you might have, since the rack rails are connected to=20 the chassis of other equipment, there is a chance that moving the=20 gear might solve the problem. Well after reading all of this, you get the idea that you=20 have to isolate each piece of equipment from everything else, connecting = it all back together one piece at a time. We first did the Power Amp. =20 Next the console. If the system is clean, then we'll connect one synth=20 or processor and check for hums and buzzes. If it causes a hum, you'll=20 follow the basic steps above, and trace the problem. Some pieces of = gear=20 just damn well causes hum from faulty engineering and design, and you'll = have to isolate these via audio transformers. But most will connect up = clean. =20 You have to check each time you add a piece of equipment: does it cause = a hum=20 in the system, or are there new pops or static? =20 If so try a ground wire between chassis, a transformer and so on. =20 One thing more: Move those dang AC Plug-In Power Cubes aka "Wall-Warts" as far away from the console, power amp, and ANY audio wiring. =20 Those things are the cause of most of the hums I get called in to fix. =20 They emit large magnetic fields which are easily picked up,=20 so move them away from your system!=20 =20 In a large top-of-the-line studio, we'll go as far as isolating=20 each piece of gear from the AC plug ground and run a separate chassis=20 ground wire back to the main studio ground (we call this "Technical = Earth"),=20 then we'll connect this "Tech Earth" back to the main AC ground,=20 and/or a large copper rod driven 18 feet into the ground. =20 Thus every piece of gear still has AC fault protection, but no grounds=20 are tied together. This kind of system is what's known as a STAR-GROUND. = =20 This is a time consuming and complex wiring scheme, but is always = fool-proof...=20 well almost.... even the best designs sometimes fail. Also in a 'Star-Ground" system, the audio ground wires are never = connected to any 2 pieces of gear... each ground is connected to the output only, and = with the exception of all Mic Cables and Mic wiring to the console, = Audio grounds are not connected between pieces of gear..... this is AUDIO = GROUND, not AC Ground.... only the audio ground wire is lifted. This prevents (in a perfect 'Star-Ground') creating 2 or more paths of ground between pieces of gear.... since the audio cable never connects=20 two Audio grounds together, the only common Audio ground will be the=20 very thick 'Star-ground' wire which connects all Audio grounds together at one place only.=20 You may find some piece of gear that just requires audio transformers=20 to eliminate ground loops. But you'll find that with most of today's=20 equipment, you really don't have to go as far as all this, and with a=20 few hours of patient troubleshooting, you'll be able to make your=20 project studio much quieter. NEVER cut or lift the 3rd grounding prong from ANY AC cable!! NEVER remove chassis ground - this is for protection against = electrocution!!! A "Star-ground" set-up should never leave any piece of gear ungrounded = to=20 AC ground. Each piece of gear MUST be grounded for safety. =20 Now here are a couple of trade secrets...the Ultra-Secret=20 "Audio-technician Guild" will come after me for telling you this stuff!! #1 All consoles want to have their Monitor Volume controls at about=20 the 1 or 2 O'clock point. That's where you get the best signal-to-noise = levels, which means quieter monitoring. So play a CD or some music = through=20 your mixer, set the faders so your meters read normal levels (for VU = Meters=20 this means peaks of about +2 VU), and turn the Monitor Pot to the 1 = o'clock=20 position, and turn DOWN the Power Amp levels until the music is at a = "normal"=20 listening level. That's the level you want from your power amp. 1 = o'clock,=20 normal, 4o'clock LOUD! If you have your Power Amp turned way up, like = most=20 small studios do, all you're going to do is amplify "normal" hiss from = the=20 console. Remember that everything has some noise, so if you turn your = power=20 amp all the way up, even the best of consoles will sound noisy, even = though=20 the reality is that the system is very quiet!! If your Power Amp = doesn't=20 have level controls, have your local tech build some for you. #2 Move those dang AC Plug-In Power Cubes aka "Wall-Warts" as far away=20 from the console, power amp, and ANY audio wiring. =20 Those things are the cause of most of the hums I get called in to fix. =20 They emit large magnetic fields which are easily picked up, so move them = away from your system. One client extended the wires from the = transformers=20 to the equipment, and moved them 6 feet away from any audio cable .. And most of her irritating hums vanished. #3 If you have a buzz that seems to grow slowly in volume then slowly=20 diminish, the odds are that you're picking up the 60 hertz signal from = your=20 local TV station. Sorry, but you'll have to get a good technician, and = even=20 then you might just have located your studio where one shouldn't be. If = you=20 have a buzz that seems to come for only short pulses, always at a = constant=20 level, then it could be a pulse riding in on your AC lines, and this is = again=20 very difficult to fix. Try to see if it might be caused by lamp dimmers = somewhere in the house, a bad florescent lamp or that old 'fridge = turning=20 on and off. If the buzz more or less comes on and stays there, try and=20 document what time of day it happens... I once traced such a buzz=20 down to a large Neon "Safeway" sign a block away, turning on each = evening. =20 I was able to "Neon-proof" that system, but you can sometimes get the=20 store owner to fix the problem sign. And sometimes just knowing why = things=20 happens makes them less irritant. #4 Computer monitors are notorious for causing hums, and you can=20 easily trace this just by turning on and off the monitor of your = computer. =20 If you get a buzz or hum when its on, only changing the position and/or=20 increasing its' distance from the console will help. #5 When you stack various pieces of equipment on top of one another,=20 you might find that one piece of gear has it's internal AC power = transformer=20 in a spot that makes the equipment just above or below it have an = audible hum. =20 Always try turning off pieces of equipment around any gear that seems to = have=20 a hum when you can't eliminate the hum with transformers. Once you find = the=20 offending unit, just move it to another spot, and try it again. #6 Get two good audio transformers and build yourself an isolation box. = There are times that nothing but transformers will eliminate hums, and = if=20 you've got friends and clients bringing in their own equipment, you can=20 save hours of frustrating troubleshooting by just using transformers if=20 their gear causes a hum. #7 Always match levels and impedances. Microphone inputs are a poor=20 place to put line level signals, but lots of studios try. If you must = use=20 your mic inputs for non-mic signals, either use a "Matching Transformer" = which not only isolates the equipment, but matches the levels as well, = or=20 have your tech build you a "pad" which will reduce the level from Line =20 down to Mic level. I just converted 18 Mic inputs of a console for line = level use, making all the changes in each module. That way this client=20 could have two line inputs for most of his console modules, and still=20 keep a few unconverted modules around as normal Mic inputs.=20 Remember that the impedance of a mic is about 200 ohms (very low) and=20 the impedance of most Mic Pre-amplifiers is about 1,500 ohms (this makes = for lower noise in Mic Pre-amp designs, which we'll talk about in = another=20 article). But most of your synths and equipment want to feed their=20 signals into 10,000 ohms resistance (known as "High Impedance"). =20 Some equipment can feed low impedances, and some equipment can't.=20 You end up by getting more noise and distortion than you should if you=20 connect gear that can't work with vastly incorrect impedances... Oh,=20 don't forget that most mic inputs also have an output... 48 volts = phantom=20 voltage to drive condenser mics! Very bad for most anything but a MIC!=20 Make sure that you never have phantom power ON if you have to connect=20 synths into mic inputs! =20 #8 You'll find that your system will normally be in it's quietest=20 state when everything is powered up. It isn't fair to have some=20 things turned on and others off, as impedances change when power is=20 turned on to a piece of gear. So almost always have everything "On",=20 even if you're not using it all. #9 Try and "hit" the Input of effects units with a good strong signal, = and reduce the Effect's output level control a bit. Lots of reverbs and = delays have background noise, and you'll help reduce this by turning the = Output down. Also don't use lots of compression unless you need to,=20 compression will lower the signal-to-noise ratio of that track, and = unless=20 you also use a noise gate along with your compressor, you'll be adding=20 unwanted noise. =20 #10 Less is More. Try using good recording technique rather than loads=20 of effects on your tracks. It's better to have a poor recording of a = killer=20 performance, than a great recording of a dull boring performance. =20 Everyone still buys CDs for the music, not the noise levels.
=20 That means the chassis of each piece of gear is connected to a good AC = ground. =20 This is so that if there is a fault in one piece of gear, you, the user=20 cannot be the "ground" for AC current. That 'third prong' on your AC = cable=20 connects the chassis directly to AC ground, and once you use an adapter = you must=20 be sure that there is a ground wire between that gear's chassis and good = AC ground. Never remove chassis ground protection!! In major studios we use a system called a Star Ground. Then we'll=20 make sure that there are no cross grounds in the audio wiring, as well = as=20 in the AC cables. Everything is still connected to AC ground via good=20 individual ground wires. This eliminates almost all ground loops, and=20 still insures a safe system. Plus it makes sure that all "Zero Volt=20 References" can stay exactly the same. We never remove grounding = protection. In a home or project studio, this same attention to system grounding=20 is important. You've got to insure not only that you system is quiet, = but=20 that it's safe too. So make sure that there is always a ground path for = each piece of gear via the AC 3rd prong ground. =20 Never eliminate a ground!!!=20 Most modern equipment, there is absolutely no reason to lift the third=20 prong of the AC cable, and you should NOT do it in any case. =20 Finally, don't over burden your AC wiring. Your house wiring is=20 meant to supply normal household currents, and isn't designed to be at=20 maximum levels for long periods of time. =20 Don't have lots of AC outlet strips connected together into one wall = outlet. =20 Make sure that no AC cable is getting warm when it's used. =20 There was one project studio I was in where the guy had 5 AC strips=20 daisy-chained into one wall outlet. That first AC strip wire was=20 carrying all the current of the entire chain and was getting hot=20 to the touch, making his whole set up a fire hazard. Don't do this!! Make SURE that no AC cable is 'frayed' or has lost it's outer cover. =20 You should NEVER see the individual AC wires ever! Lastly - you should NEVER do any AC wiring yourself. =20 You MUST hire a licensed contractor or other highly qualified (and = legal)=20 person to do ANY AC wiring.NEVER, NEVER, NEVER unground any piece = of gear!!!=20
Good Quality Audio Transformers are available from: Jensen Transformers (some of the best transformers available) (818) = 374-5857 Triad and Stancor both available from Newark Electronics (many locations) there are other manufacturers of Transformers too....=09 Transformers =09 =09 One of the easiest ways to eliminate ground hums is to isolate the = offending=20 equipment via input and output transformers. These things do amazing = things=20 in the audio world and are often contained in the best equipment found = in the=20 big studios. Since the whole principal of a transformer works on a = transfer=20 of only magnetic flux, there is absolutely no physical contact needed = between=20 two pieces of gear to get an audio signal through. If you need either to = quickly=20 remove a ground loop caused by poor grounding, or to transform balanced = to=20 unbalanced signals, grab a transformer. But transformers aren't perfect. Expensive transformers are about as = near=20 perfect as you can get in the audio world, but you pay for the = engineering=20 and construction quality. Lesser transformers suffer from their design = and=20 the way in which they're built, but if you match your requirements to = the=20 correct transformer, you need not spend an arm and a leg to get what you = need... For the Pro studio, operating at normal +4 levels, you'll have to go for = the=20 top end of transformers, and I prefer Jensen Transformers (818) = 374-5857,=20 though there are a few other top manufactures around. But you're gonna=20 pay for top line transformers... the Jensen JT-11P-1 transformer = currently=20 sells for $63.49 each, then you have to drill out a case for your = connectors=20 and wire them yourselves. But here you can put in up to +17 dB before = you=20 even hit 1% distortion at 20 hertz! Killer performance!! These are the = puppies=20 I install when I need top studio performance. Transformers can do other things besides isolate two pieces of = equipment. =20 You can use a transformer to step up (or down) signal levels. So say = your=20 console is a Pro Standard +4 dB output unit, and you need to drive a=20 -10 dB device... you could turn the input levels of the device way down = or run the console level way down. But it's always better to run things = at their optimum points, so if you could, you would want the console = running=20 at +4 dB and the next device at -10 normal input fader levels. A = step-down=20 transformer can do the trick for you, so everything is right where it = should be. =20 If you need to hook up both a balanced and unbalanced device to the same = output, you should isolate the unbalanced gear via a transformer, or = else,=20 once both are connected to the same point, you've unbalanced the signal = to both. =20 And if you're working a remote, the only safe way to split mic lines to = send=20 the same mic signal to more than one mixer is to use a "Splitter = Transformer". =09
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