Dirty Power

May 10, 2012

Dirty vs Clean Power

Hello folks!  Welcome back to The Corner.  This week we’re going to discuss a source of noise that not everyone is aware of, dirty power.  Dirty power basically refers to line noise coming from older wiring and improperly wired AC circuits found in older homes and some small venues.  Dirty power can cause major noise issues and can drive a lot of people insane troubleshooting their rig when the problem is actually not in their rig at all! 

So what is line noise?  To put it as simply as possible, line noise is random fluctuations and electrical impulses carried along with the standard AC current.  This can be caused by fluorescent lights, large appliances, nearby large transmitters (radio stations), and older AC circuits that haven’t been updated to current electrical standards.  Line noise can translate directly from the wall into your guitar rig causing many people to pull their hair out trying to find the source of the noise.  Unfortunately, there are limited options but there are a few things you can do to be prepared for any sort of noisy power.

Knowledge is Power

The first step in fighting this annoying source of noise is knowledge.  First, have a basic understanding of a ground loop, what it is and how to avoid one.  When you set up your gear, make sure your rig is ground loop free.  This may not protect you from ground loops elsewhere like at a club but it will at least make sure your rig is set up properly to avoid any troubleshooting in that area. 

Second, know what else is on the circuit.  If you’re at home, check the breaker box for the plug you use and see what else is hooked up to it.  If you kill the breaker that you plug your amp into and the refrigerator turns off, then you should probably use a different outlet for your guitar.  Appliances, water heaters, fluorescent lights, fish tanks, and even some HDTVs can induce noise in the line.  Make sure your audio equipment uses a plug that only shares power in that room, this way you know exactly what else is on when you play. 

Be Prepared

Since it’s not possible to control which circuit you’re on when you’re gigging, the next step is to be prepared.  I’ve played countless clubs that shared stage power with the lighting.  The worst is dimmer switches; they seem to induce more and more noise as the lights are dimmed.   There are a few things you can do when gigging that will minimize the effects of line noise.

First, know your venue.  Most places that have live music night after night will have the stage power isolated from the lighting rigs.  This may not always guarantee a complete lack of noise in the lines but it will drastically reduce the likelihood of getting dirty power.  If you’re playing at a venue for the first time, ask them about the power.  If the booker/owner can’t tell you, ask the sound man.  Show up early and ask about lighting and power and have them show you where you’re going to plug in.  Let them know that if they have any lights on a dimmer, you would prefer they do not use them during your set.  Most venues will accommodate the artist as long as your requests are reasonable. 

Second, have a power conditioner.  I cannot stress this enough, please spend the money on a nice power conditioner that has line filtering and surge protection.  Not only will the unit protect your gear in case of a surge or brownout but most of these units have built in filtering that removes or reduces line noise.  The specifications will list a dB rating at a specific frequency.  The higher the dB rating the more filtering that is available and the quieter the unit will be. 

What to Use

Power Conditioner

When looking for a unit to reduce line noise, you want to consider your situation.  Obviously you don’t want to spend hundreds of dollars on a line conditioner with 8 outlets if you only plug in your amp and pedal board power supply.  Also, if you never play out and only play at home, one of these units may not be the best investment.  In this case, check out a unit like the Ebtech Hum X or the Audio Prism Quietline.  These are individual units that filter one plug at a time and are perfect for home and studio use.  They do work for gigs as well but if you’re a gigging electric guitarist then you likely have a band and for a band there is a better solution in my opinion.

The band situation is where you will want to consider a more expensive power solution.  In this case that eight outlet power conditioner that costs several hundred dollars might be the way to go.  Think about it this way, that one unit can protect not only you but your other guitarist and bass player from noise and power damage as well.  Instead of hauling around a few small Ebtech units (which do not protect against power surges) you might as well have one master unit for the entire band’s gear.  This way you only need one outlet on the stage and the larger cost of the unit can be defrayed by each band member pitching in.  Make sure the unit is rated for the power you require and that the gear you’re plugging in isn’t going to draw excessive amounts of current and this solution will work just fine.  It also prevents ground loops in your stage setup.  Companies like Furman, Tripp-Lite, and Monster make high quality, filtered power conditioners that will eliminate noise and stabilize incoming line voltage.

The one thing you do not want to do when faced with noise is use a ground lift.  Those little “three-to-two” prong doodads that the kid at Radio Shack is always quick to suggest are a bad idea.  They can lead to injury or death and that goes for your gear as well so just don’t do it.

Ebtech HumX

Well there we go folks.  Unfortunately, unless you’re a qualified electrician there’s not much you can do to eliminate dirty power but there are steps you can take to be prepared to fend it off and protect your gear.  A small investment can save a lifetime worth of frustration, especially when you’re on the road or on your own dime.  Thanks for reading folks.  We’ll see you next time, in The Corner.


  1. Sherwin says:

    Better to start selling Sanyo pedal juice then .

    posted on May 10, 2012 at 6:53 pm
  2. Lenny says:

    I recommend buying one of those Radio Shack plug-in power testers.  I once found two outlets in a club’s ‘stage’ (i.e., the area they cleared out for the band to set up) that were wired out of phase.  If you plugged the PA into one and your amp into the other, you might find yourself channeling some voltage through your lips (ouch!).

    posted on May 11, 2012 at 2:24 am
  3. dm says:

    Hmm.  Having been in the guitar/amp demo room in the Pearl, I’m not sure PGS is qualified to write this article.  Dirtiest power I’ve ever heard.

    posted on May 11, 2012 at 2:24 am
  4. KEN LEWIS says:


    posted on May 11, 2012 at 2:24 am
  5. Mr Confused says:

    a buttplug could be considered dirty power too??

    posted on May 11, 2012 at 2:35 am
  6. Sam says:

    Does anyone know any companies that make things like this in the UK/for UK style plugs?
    Really interested in getting something like this but can’t find any that would suit our sockets :(

    posted on May 11, 2012 at 3:26 am
  7. KEN says:


    posted on May 11, 2012 at 3:44 am
  8. Steve J says:

    I have been an audiophile for many years and clean power makes a huge difference in an audio playback system.  I’m a little suprised that this subject is not talked about more.  I have dealt with this issue in a systemic way to clean the power for my whole house.  It has been very effective in my audio system, and I assume it has a similar effect on my guitar rig.  I guess I will find out if I ever play somewhere other than my bedroom.

    posted on May 11, 2012 at 3:49 am
  9. Bill Wood says:

    Sam. Try a company called Russ Andrews. They supply musos and studios, be warned though, prices range from Hummmm, to “HOW MUCH”!!!!!!!!!!!!!!!

    posted on May 11, 2012 at 4:06 am
  10. Lou says:

    About 12 years ago I purchased a Professional Power Conditioner/surge protector from a Florida based company called TICE.  I was big in to Home Theatre and this unit had 16 outlets in the back and had a lifetime warranty.  Not cheap at $1000 it has served me well with clean power for my $20K Plus Home Theatre but would also work for any band. I agree with the checking your breaker box to see what is hooked up to the outlet your plugging your guitar amps into.  In my old house the wiring was old so I had a special Hospital Outlet installed and it ran straight in to my fusebox, it did not share power with anything.  Many guitarists don’t know this either, the power cord that came with your amp may not be a good one, some are & some are not. If you have a thin lightweight one consider getting a good 100-150.00 Power cord for your amp.

    posted on May 11, 2012 at 5:32 am
  11. Sam says:

    Thanks, Bill!
    Very kind of you - I’ll have a look :)

    posted on May 11, 2012 at 5:48 am
  12. Dave says:

    Really? I’ve been using “those little “three-to-two” prong doodads” (AKA ground lifts) for years somewhat effectively and have never experienced an injury or problem with them. I’d like to read more of why exactly you guys at ProG. feel they’re not safe (along with some corroboration/source for your assertions).

    posted on May 11, 2012 at 6:32 am
  13. Joe says:

    Would it be fine to run a hum x in front of a surge protector or would I need multiple to clean the power on my amp, pedals and fx rack?

    posted on May 11, 2012 at 8:28 am
  14. DC says:

    Im surprised Andy go more into detail about ground loops as well as the other things. Ground loops have kinda always confused me for some reason. Also, what about converting a vintage 2 prong plug with no ground and internal transformer rinto a three prong unit ? A vintage mxr for example?

    posted on May 11, 2012 at 9:13 am
  15. DrDan says:

    Furman has systems to work just about anywhere on the planet, take a look at their website, they have some useful information.

    posted on May 11, 2012 at 11:42 am
  16. Bryan says:

    The 3 to 2 prong power plug adapters, a.k.a. ground lifts, can introduce a potentially deadly situation into your rig.  The purpose of the third pin ground on the power cord is to connect the chassis of the electronic equipment to earth ground.  This is for SAFETY reasons.  For example, if you remove the third pin ground connection from your amplifier’s power plug because doing so gets rid of the hum when you play in that little dive across town, you are opening yourself up to being electrocuted if a component in your amp fails.  Besides, the problem wasn’t in your amp.  The problem was in the electrical wiring in the building.  If the owner won’t fix it, find another gig.  He’s putting your life in danger.  Also, try running all of your equipment from the same phase on the same breaker box.  This can be a source of noise, especially if the house mixer is plugged in on the other side of the room.  And get one of those 3-prong plug-in testers with the 3 little lights on them and make sure EVERY outlet you plug into is wired correctly first.  If the tester shows backwards wiring or a missing ground, don’t use that outlet.

    posted on May 11, 2012 at 12:37 pm
  17. Russ says:

    Fast solution that a local electrician can do is wiring one circuit (or more) into a ground rod that is separate from the building ground (normally a copper or galv water source).  Works and doesn’t cost all that much.

    posted on May 12, 2012 at 5:50 am
  18. blueslide says:

    this happend to the other guitarst in a old band i played with. I broke a string did a quick change during a set forgot to snip the string jumped back on stage no problem Not!!! Our amps were on seperate phases. So when the big allman bros twin solos at the end of Ramblin man happned my loose string brushed across his cheek
    Hello, that got his attention. This stuff is no joke do some reasearch it could save your life








    posted on May 12, 2012 at 10:22 pm
  19. pinkjimiphoton says:

    yah, you can use one of them hum eliminators first in line before a power strip, will work fine.
    all it is is a 1:1 transformer…ie voltage from the wall goes thru the primary and back to the wall, and induces flow in the secondary…completely physically isolated from the wall that way.
    the ebtech hum things work ok, but any isolation transformer will help.
    if you don’t know your way around ac mains wiring, do NOT fuck around trying to make one, it is a very simple thing, but could kill you.

    posted on May 13, 2012 at 3:43 am
  20. Lou says:

    pinkjimiphoton, when you say power strip your surely not talking about one of those $10-15 models purchased al Wal_mart are you?  I would not plug anything that cost more than a alarm clock into one of those.  I have gone to more house fires because people overload those things during Christmas it isn’t even funny.  A surge protector at the minimum, not a plain old power strip. Monster Cable, Furman, An old company called Max Sat. It is very important to remember that no matter what your plugged in to if you get a Direct hit by lightning Nothing can stop it. Not for the home user anyway. Even my $1000 Tice Power Center won’t stop a direct hit.

    posted on May 13, 2012 at 7:36 am
  21. pinkjimiphoton says:

    yah,  power strip is fine for the average guitarist. i use a monster cable one, but am not that sold on it being any better than any other ones.

    an isolation transformer has no physical connection between the primary and secondary. that’s where the term “isolation” comes into play. it induces (induction, if not familiar with the concept, look it up) the same current flow in the secondary as is drawn by the primary. it’s an over simplification, but for all intents and purposes, a hum eliminator “floats” everything on the secondary.

    without understanding inductance, you won’t understand what i’m talking about, but yah, power strips are fine if as you say not overloaded. used ‘em for decades and never had any issues whatsoever. you can spend all kinds of bread if you want to, or go cheap…or build your own, if you understand what you’re doing.

    btw….you’re not supposed to leave any kind of power distribution box plugged in during a lightning storm lou. technically, it shouldn’t be plugged into the wall unless you are using it.

    a simple cheap power strip by itself may cause issues if you draw more from it than it’s rated indeed…but in the case of an isolation transformer, you’re not physically even connected to the wall really…unless you were to short the iso itself.

    you don’t have to spend a crazy amount of money on things to have perfectly suitable gear.
    anything less than a unit that offers uninteruptible and regulated power is nothing but a fancy power strip…maybe with a varistor and choke to try and reduce line hash.

    there is a huge difference between a regulated power supply (what was mentioned in this article) and a power strip…the first being an active device, and the latter a passive.

    but monsters and stuff like that? still a power strip in the end.


    posted on May 13, 2012 at 8:31 am
  22. Alceu says:

    Just a note: When getting your line conditioner, make shure it was made specifically for Professional Audio Equipments or Audio Instruments, like Furman, mentioned before. In the market we have also high quality No Breaks that have all the specifications mentioned before like the line conditioners, cause it is a kind of conditioner (power/line regenerator), but it comes with a battery to keep you playing even when power goes down, and some heavy duty ones comes also with battery direct senoidal line input source, witch remain always recharged, so, it is not like a bypass system, but you can only use the energy from the batteries, keeping you from using the local line source (a kind of stealing the local energy by batteries, then using it with the necessary peaking demand, that you cannot find on usual wall plugs) for you to keep even more protected, clean, and reach audio peaks..  Do not misunderstand Audio No Breaks, or Power Conditioner appliances, with PC No Breaks, Tv’s, and general eletric equipments at home, or Professional Video, even at clubs. When picking up an Audio proper conditioner, you must know that they are made for higher punches of energy, and peak levels that are demanded by the band or powered systems.

    posted on May 15, 2012 at 1:34 am
  23. Rob says:

    My house was built in the 50s and a lot of the wall outlets aren’t grounded. Will a HumX work on those?

    posted on May 15, 2012 at 6:27 am
  24. pinkjimiphoton says:

    yah, it’s still an iso transformer, but you really want to have a ground. be careful mate. no ground can be deadly…the hum x is still grounded, it just floats the pos/neg…sorta. it may help with hum, but it won’t keep you safe, if that’s the question.

    posted on May 15, 2012 at 6:31 am
  25. Rob says:

    Yeah, it’s the hum that I’m trying to get rid of. It can get loud, but when I touch the strings the amount of noise reduces considerably. So anything that cleans up the power coming out of the wall should help. I’ve got a Monster power strip I’ll try plugging into the HumX. Thanks.

    posted on May 15, 2012 at 6:57 am
  26. pinkjimiphoton says:

    hi rob,
    it’ll probably help some…if you’re using a monster power strip, don’t plug your amp into the socket marked “amp”...i was cautioned when i bought mine that that outlet has no filtering associated with it…dont know if all are like that, or just the early ones like mine.

    if you are playing a tube amp, and getting a bad hum that won’t go away, particularly if you bend a string and hear an almost off-pitch hum going the opposite of your bend, it is most likely distressed filter caps or a blocking cap that’s shorting…take it to your tech and have the filter caps serviced. not only can it save your amp, but it can save you as well….especially if you don’t have the option of having your chassis ground physically connected to earth.

    posted on May 15, 2012 at 8:40 am
  27. Bryan says:

    Hmmmm…. I’m a little curious about touching the strings and the noise goes away.  Is your guitar shielded in the control cavity?  This sounds like a radiated noise problem.  Do you have florescent lights?  Single coil pickups?  I bring this up because your AC power can be clean and you can still have the symptom you describe.  You probably should look at having an electrician install a safety ground, or maybe run a grounded circuit on a seperate breaker to the room where you plug in your amp.  Or take your rig to a friends house with more modern wiring and see what the noise is like there.  And throw one of those little 3-pin plug testers in your gig bag to test power outlets before you plug in your amp.  Getting lit up can be a thrill but its definately no fun.

    posted on May 15, 2012 at 9:57 am
  28. Adrian says:

    Nothing similiar similiar to Hum X can be found for europe AC power and plug types, anyone using this type of gear? (model HE-2)

    posted on May 15, 2012 at 8:58 pm
  29. Steve J says:


    You might want to check out Alan Maher designs.  You can find him on Facebook.  He lives in Germany and produces a wide range of power products that deal with the issue on a systemic basis.  His applications were designed for audiophiles, but clean power is clean power.  He is also one of the premier sound guys for major rock shows in europe.  He knows his stuff. 

    posted on May 16, 2012 at 3:09 am
  30. dudleydorightdad says:

      Just a fair warning Russ, it may sound like a quick easy fix to drop a separate ground rod and thus an isolated ground but if you ever have a second read up on the subject of isolated grounds in the NEC.(National Electrical Code) You will find that doing so is not only illegal, but about as bad as you can get safety wise as you are creating what I would call the mother of all ground loops. A true isolated ground circuit utilises the normal equipment grounding conductor to ground the box and any metal parts at the outlet while the isolated ground is used only to ground the pin for that outlet. But the isolated ground is connected to the equipment grounding conductor and the grounded conductor at the service entrance to the building. If you do not know or understand the 4 items I referenced in the last sentence I would suggest you either educate yourself properly or hire a trained proffesional electrician. Not a home repoo hanging around the lot but a person certified and knowlegeable in the electrical field. Sure I know, anybody is smart enough to run a wire and hook up a receptacle, and if so then why in this age of smart everything are there still lives being destroyed from either fatal fires or electrocution when we have had electricity in our homes for as long as we have. The NEC is written by the NFPA which is the National Fire Protection Association and it is updated every three years. Probably not worth your time to check the code if you are immortal, but if you are human then maybe you or your family might be worth the small in the big picture investment to ensure your safety from what I can guarantee without prejudice is a most horrific painful way to die.

    posted on May 16, 2012 at 9:25 pm
  31. Keith says:

    Dudleydorightdad is correct.  For those looking to understand a ground loop, check the wikipedia entry for ground loop.  It’s a bit on the ‘mathy’ side so I’ll simplify by explaining the ‘voltage divider’ concept they reference in their explanation.  If you put two identical value resistors in series (end to end) and then put a voltage across that end-to-end pair of resistors the voltage you’ll measure at the junction between the two resistors will be exactly half of the total end to end voltage.  So, if we’re talking 120v total, you could get 60v suddenly appearing at that junction.  R1 is the load provided by your amp and RG is the resistance between the ground pin of your outlet (due to faulty wire, undersized wire, loose wire nut, oxidized wire under the screw in the outlet, etc, etc).  When RG is not zero (and it never is really zero) you will have some amount of ‘float’ but properly grounded eqpt that voltage is negligible.  If you’re plugged into an outlet with a really bad ground and THEN if the insulation around the windings in the primary of your guitar amp’s power transformer becomes frayed/burned and shorts to chassis ground.. the amp will keep running (giving you no clue there’s a problem) but now the chassis ground is floating at some voltage.  No problem until you’re holding your guitar strings and touch either a microphone or your buddies guitar string that’s connected to a different power outlet accross the room that’s properly grounded.  You (and I mean you as in… your body) then complete a circuit and at minimum enjoy a little tickle, at worse, you get knocked out cold like Ace Frehley did one time in Florida at a concert.  It can be lethal as well.  Bottom line, my suggestion is to do what Ace did.. he and his bandmates converted to wireless rigs.  They’re really cheap these days (I use the little Samson Airline 77’s and think the world of them) and although it won’t address any problems with hum, it will guarantee your guitar will never become a threat to your health (unless you’re practicing too loud at home after being repeatedly asked to turn down by your lady’).  Comments/corrections welcome, nobody’s perfekt… ;-)


    posted on May 17, 2012 at 7:23 am
  32. dohootowl says:

    I greatly appreciate the sharing of this information here!  I’ve often worried about the quality of electrical installations at a lot of the clubs where I’ve played, and for good reason.  I have never played wireless, but will certainly consider it now.

    All this talk leads me to believe that I need to study electronics/electrical engineering.  Although some of you have attempted to break things down to provide a better understanding, I find that your breakdowns need breaking down for those of us that don’t have an EE or an electrician’s education.  It’s good for us to educate ourselves.  Any primer suggestions for beginners?

    posted on May 19, 2012 at 12:05 am
  33. pinkjimiphoton says:

    the easiest way imho is start small, learn to build your own devices… is the best resource for that probably, etc…

    start small, and work yourself in. a good working math ability helps.

    so does google…you can find out about everything there.

    my humble knowledge started when my tech got sick of fixing my marshall every week when it would blow up , and gave me “inside tube amps” by dan torres…not the definitive tome, but it got me started with enough knowledge to repair that jcm800, and eventually build the amp i play on stage today.

    start small with simple dc projects with low voltage, and work your way up.

    oh yah…especially while learning…keep your spare hand in your back pocket. even us guys that have been doing this for a couple decades sometimes forget that, and get fried.
    i got hit with 560vdc across the chest working on an old ampeg once cuz i wasn’t paying attention, and it was no fun and i am VERY lucky to be cyber-scribbling this.


    posted on May 19, 2012 at 12:14 am
  34. Keith says:

    Google Kendrick Amplifiers.. the guy who founded/runs that company is Gerald Weber.  I have a BSEE and wish to God I had this guy as my teacher back in college… or that I had his books or DVD’s before I took my classes in circuits.  In the college classes it’s so dry and dusty and heavy on the math but, to me at least, I found Gerald’s explanations so much more ‘common sense’.  In particular the DVD “Understanding Vacuum Tube Guitar Amplifiers” is a great primer that takes you from basic discussions about what is voltage, current, resistance, etc and walks you all the way through explanations of how early American tube amps worked (Fenders) and moves up from there through the British amps (Vox/Marshall) and just really does a great job of covering a lot of ground without being too much in the math.


    posted on May 19, 2012 at 1:23 am
  35. pinkjimiphoton says:

    keith is on the money, there, weber is WAY more in-depth than torres.

    torres is good if you know squat and don’t want to understand what you’re doing.

    but really, better to start with stompboxes…guitar amps are working with lethal voltages, and ONE mistake can kill you. stompboxes you may screw the circuit up and smoke it, but THAT you’ll probably survive! ;)


    posted on May 19, 2012 at 1:46 am
  36. Keith says:

    @pink - Can’t argue that… if you’re not SURE what you’re doing, don’t go poking around in a tube amp.  They have large capacitors in their power supply that retain a charge for some time even after being unplugged.  You can hold a large value resistor with a pair of long nose pliers and touch the legs of the resistor accross the cap’s to make sure they’re discharged, if you’re going to ‘go there’ but learning some basics by building some kits from BYOC dot com is a great suggestion.  Bottom line, I enjoy knowing how things work and what makes them sound the way they do, but like Clint said… “A man’s got to know his limitations” and I see no shame in letting a pro service my amps for anything beyond replacing tubes.

    posted on May 19, 2012 at 1:57 am
  37. pinkjimiphoton says:

    hi keith,

    byoc is good, a little pricey, but a great starting place. mammoth is good also for complete kits.

    if you’ve never read the torres book, it’s worth the 50 bux just in that it will enable you with little understanding to not only maintain and repair tube amps, but troubleshoot them without opening them….and gain enough “layperson” info to make you realize it’s not rocket science at all.

    but PLEASE…do not open your amp and fuck with it…there are protocols that must be understood and followed, and there’s people on this planet that will be bummed much worse than you if you kill yourself trying to save a couple bucks. it truly isn’t worth it.

    that said tho, once you understand the dangers and the techniques to minimize them, building/repairing/modifying your own stuff is pretty hard to beat.

    at this poing, i play many guitars i’ve built from parts/kits, everything on my pedalboard except my tc electronics delay i built myself, and i play thru my own amp…it is an incredibly rewarding experience.

    so…learn all ya can, and keep one hand in your back pocket.


    posted on May 19, 2012 at 4:12 am
  38. dudleydorightdad says:

    Dohootowl, just spent over and hour giving a concise almost 11,000 word explanation of your modern and not so modern electrical system and gronds, grounding, grounded etc only to have it tell me there was a 5000 word limit and offered me the option of returning to this screen BUT FRIKING DELEATED THE ENTIRE POST.

    posted on May 19, 2012 at 4:20 am
  39. Keith says:

    @Dudley… BUMMER!!  I hate when that happens!!
    @Pink… Mammoth is awesome.. thanks to hipping me to them, I’d never heard of ‘em before today!  ;-)  Cool!!

    posted on May 19, 2012 at 6:56 am
  40. pinkjimiphoton says:

    and if ya need components, checkout

    they don’t have EVERYTHING, but their prices are great and their min order is only 5 bux.

    i use ‘em all the time, pretty much the best deal in terms of most electronic diy stuff out there.


    oh yah, you may wanna check out, too…they make most of the kits mammoth sells.

    posted on May 19, 2012 at 8:01 am
  41. Keith says:

    Cool!  Thanks for the info.. will definitely check ‘em out!!

    Have a great one!

    posted on May 19, 2012 at 8:11 am
  42. Elias Simon says:

    I realize I may sound sophomoric for saying this, but I’ve heard that the dirty power problem is a MYTH and I’m strongly inclined to believe my sources, both as a member of the Audio Engineering Society and as an electrical engineering major.

    First, as a member of the Audio Engineering Society, I can cite Bill Whitlock’s tutorial, “Design of High-Performance Balanced Audio Interfaces” for explaining the source of the noise often associated with dirty power and very specifically addressing the myth of the problem. Whitlock explains that the physical distance between separate power outlets can cause the third prongs to conduct current when the two outlets are joined with a signal chain. This leakage current between outlets is a major source of noise. Disconnecting the third prong breaks the circuit that conducts this current, which is why it eliminates this noise. What Andy says about this being unsafe is all too true, though. Don’t mess with that third prong.

    Second, as an electrical engineering major, dirty power makes no sense from a technical electronics perspective. That 120V 60Hz sinusoid is going to get passed through the same basic parts of a power supply and the result is always going to be a DC voltage with a negligibly small amount of ripple. I’ve built such devices and can tell you first-hand that you cannot tell the difference between perfect and imperfect sinusoids after they’ve been processed.

    What you can do is make sure that you only use closely spaced outlets. Again paraphrasing Whitlock, power conditioners often get credit because they simply offer a bunch of closely spaced outlets. The parasitic inductance (not ambient electromagnetic fields) that causes the leakage current can’t become problematically large without long lengths of wire between outlets.

    In summation, dirty power may exist, but it doesn’t have an effect on your signal. Before you buy an expensive power conditioner, try getting all of your power from a single power strip and you’ll go a long way to eliminate noise from your signal chain. If anyone has any other information, feel free to email me at

    posted on July 24, 2012 at 4:34 am
  43. pinkjimiphoton says:

    hey man,
    there’s a lot more noise in that ripple than you think. check it with an oscilloscope..
    turn on a blender, fridge, air conditioner, etc etc….

    you’ll see it’s effect. the whole reason we build power supplies rectified in audio gear is to minimize that ripple.

    all too often, we’re using dc amplification to amplify our pesky audio signal. the more hash and noise gets thru, the worse it gets. that’s why the first stages of an amplifier have the most filtering.

    with unity gain devices, it’s not a worry.

    tell that to a dimed marshall in some crappy little club with everything…dishwashers, blenders, ac, fridge and lights on…. you’ll get quite an education your EE degree didn’t teach you.

    i’ve played rooms where i have to literally forego the use of certain effects…ge fuzz faces and digitech whammys in particular…because way too much noise (ripple) is on the mains.

    i’d humbly suggest one think outside the box on this one, and understand, there is a huge difference between filtered and conditioned ac, as used by most audio engineers, and the conditions of the average nightclub.

    not even in the same universe, bud. peace

    posted on July 24, 2012 at 4:42 am
  44. Keith says:

    @Elias - All you have to do is Google “EMI Line Filter” and you’ll see there are countless big name manufacturers (Coilcraft, TDK/Lambda, etc) selling A/C filters, so dirty power is definitely not a myth.  Non-brushless a/c motors are the worst offenders, especially as their brushes/commutator wear down.  As the brushes/commutator open and close the circuit to the windings these power ‘spikes’ put a nice little ripple out onto the mains which can definitely be heard on high gain amplifiers.  It helps if your guitar amp isn’t on the same breaker as the a/c motor of course.  As for Whitlock’s paper, agreed that it’s always best to have all your gear plugged into a common outlet.  The “..generally under 10mV”  he mentions in his article is definitely enough to be picked up by a high gain amp since the voltage coming from a guitar pickup is also down in the mV range.

    posted on July 24, 2012 at 6:31 am
  45. dudleydorightdad says:

      First, on iso transformers, be aware that there is no physical connection between the windings but the ground path is not interupted unless it is clearly labeled and listed isolated ground device.
      Second, no offence or derogitory intent to an engineering degree, but many engineers rely on the book without having ever had any hands on electrical experience. Again no disrespect intended, But the condition a lot of folks will encounter on the electrical line and the reason a filtered outled device will rectify the situation is that it is not a ground loop but noise in the form of EMI and RFI that originates generally in facilities with a large mix of resistive and inductive loads, large loads.IE Big motors, etc. My problems were without a doubt generated from the elevators in the hospital campus elevators less than a block from my home. And the high frequency noise, which if you heard it, sounded exactly like a motor starting, ramping up, running, ramping down and stopping. And with no direct electrical connection as my small residential block grid was not interconnected other than maybe at the substation to the hospital. And it was, it seemed, only one of the elevators causing the issue, or one that I could hear anyway. So the ripple current will sound one way, emi another, ground loops something else entirely. A very basic power filter will have a line to neutral capacitor, a line to ground and a neutral to ground pair of capacitors with a pair of inductors between the first cap and the lastr two. And throw in a few varistors to absorb the spikes. Also be aware that it used to be 110 volt service, Then 117, now we call it 120, but in the wee hours, the no load hours when everything is off but a few lights, voltage is usually AT LEAST125 volts and even a bit higher. How many thousands on ytour gear, Spend a few bucks to give them clean fuel.

    posted on July 24, 2012 at 9:10 am
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