Tagged with "hum"
Step By Step Hum Test-Simplified Tags: hum

STEP BY STEP HUM TEST

Simplified for quick and easy location of the source of unwanted hum.

There are two other articles on this site discussing hum tracking in detail.  This is the "quick and dirty" page for those who wish to run the easiest tests, quickly.  They're usually effective in the majority of cases.

An article on Wikidpedia is unusually well written, helping even beginners to understand what causes hum and how to deal with it.  It's not too technical, not overly long, and very informative.

https://en.wikipedia.org/wiki/Mains_hum

Note while a bad pickup can cause all sorts of problems... in the majority of cases the source of hum is not the pickup.  In two places in that article it states that even humbucker pickups are designed to "reduce hum" (not eliminate it 100%).  If a pickup itself were enough to eliminate all hum, companies couldn't sell hum-killer devices for high dollar.  Obviously hum must be met head-on, at the source.

FIND THE SOURCE

Blaming a pickup for hum is often pointing a finger the wrong direction.   Even a single-core pickup can have zero hum if the line power is clean.  At the same time, even a humbucker will hum if the line is "dirty".   So it's necessary to identify the true source of the hum and work to overcome it.  Thus this article.

The two primary sources of hum is ground-loop issues, and RFI/EMI (wave interference).  The source of the hum could be either or both.  But RFI/EMI can be shielded and sent to ground, so in the end it still comes down to making your instrument, amplifier and power source are properly grounded and your power clean.

I recommend Uninterruptable Power Supplies for ALL important electrical equipment (music equipment, televisions, computers, etc).  They are no more expensive than a good surge protector... and work better.  They are available for under $50 (the higher price version are to provide more power and remain online longer if the wall power goes out).  Of course a UPS is no magical solution to all hum.  In music there are many variables.  But employing a UPS to filter your power source is just one of those no-brainer wise decisions. 

 

THE STEP-BY-STEP TEST

The above principles and concepts understood, following is the step-by-step test to trace down the source of any hum issues. 

1. Install the pickup on your instrument as normal.  Your pickup may already be installed. In such case it may be necessary to check all wire connections and make sure the solder joints are neat and solid.

2.  Turn the volume to minimum, turn on your amp, and bring up the volume to normal playing level.  The GAIN should be set to minimum (gain by nature often causes noise).  Bass, mid and treble should be set to mid-range or lower (on most amps a setting of 3-5 is considered good testing range). 

3.  Touch the end of the guitar cord to make sure you have continuity and that it doesn't "roar" (too much power from the amp).  You just want a mild sound when the end is touched.

4.  Plug in your guitar.  Ignore any noise or hum (that's what we're checking and we take it for granted it's there).   Strum a few chords and notes to see if the sound is normal, acceptable sound without excessive "noise".   Excessive noise indicates an instrument, amp or external problem.   Most instruments when played should pretty much override any noticeable hum.   That's the purpose here: to make sure there's no *excessive* source of noise that might indicate more serious problems than basic hum.

5.  Quiet the guitar strings (mute with your fingers).  When the guitar is quiet, cease touching the strings.   You'll be able to hear hum (if there is any).   At this point, touch the metal sleeve on your guitar cord jack to see if the hum remains or vanishes.   If the hum vanishes when you touch the metal sleeve, that indicates a ground loop issue that will need to be traced and corrected / counteracted (thus the other two articles).

6. If there is still hum when you touch the sleeve, that is indication the hum is internal to the instrument.  The instrument itself should be checked for proper internal grounding (pickup, bridge, strings, controls), and that all areas are properly shielded against RFI/EMI.  It is also possible in this case there is a problem with the amp.  To test this plug in another instrument and see if the problem persists.  If it does, look to the amp as the issue.

7. If your amp has 3 prongs on the cord, turn it off, unplug it and plug the cord into a 2-prong wall adapter (available cheap, anywhere).  Plug the amp back in and turn it on.  If there is no hum-- the problem is definitely a wall-based ground-loop issue.   Whether there is hum or not, after a few seconds turn the amp off and remove the adapter.  A 3-prong amp should not be operated for any length of time using a 2-prong adapter (even if the hum vanishes).   But hum vanishing when using a 2-prong adapter definitely isolates the cause of the hum... and indicates how it needs to be fixed.

IF ALL ELSE FAILS...

8. This test sounds strange, but if hum persists, wrap the body of your guitar with aluminum foil and make sure the foil connects with the cord jack sleeve (for grounding).  If the hum disappears, the problem is very likely RFI/EMI interference. 

9. Then un-ground the aluminum foil from the cord and see if the hum situation changes.   This is basically a "let's see what happens" test to see if there is significant external interference.  Of course you can't play an instrument wrapped in aluminum foil-- but it will indicate if the problem is a lack of shielding... or trying to play the instrument near an excessively "noisy" device such as a computer or other electrical device that is emitting undue RFI.  If your guitar is properly grounded there should be no difference between grounding the foil to your guitar cord or not doing so. 

 

THE ABOVE STEPS should in the majority of cases help you find at least a hint of where hum problems may be originating.   In most instances the source of hum is unfiltered wall power that is creating electrical hum.  There are ways to overcome such (UPS devices, Hum-X filters, etc).  If the problem is indicated to be the amp or instrument, then of course more professional steps will need to be taken to isolate such issues.  Your local music store or a good friend with electronics / guitar knowledge may be able to help you there.

 

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Tracking Down Hum pt 1 Tags: hum noise

Click here to read part 2 of this series

 

Hum and buzz when plugging in an amp.   Annoying and frustrating.  Where is it coming from?  Is it the git, the amp or something else?

Many articles have been written on this.   Doesn't hurt to re-hash once in a while.  This is a step-by-step process for locating and eliminating hum, starting with easiest-to-check.  If you only have one set of equipment you may need to ask a friend to bring over a guitar amp and cord to double check some things.

 

TEST FOR GROUNDING ISSUES

Touch the metal jacket on your guitar cord when it's plugged into the amp.  If the hum vanishes you likely have a grounding problem somewhere.  Read pt 2 of this series for fixing grounding issues.

 

TEST THE CORD

Poor guitar cords are notorious for creating hum.  Try a different cord.  If hum still persists, you may want to invest in a  quality, shielded cord.  They cost a bit but there's a reason for that: they help eliminate external sources of hum.  If the hum disappears it's money well-spent.  If not, it's still money well-spent.

 

TEST THE AMP-  WALL TRANSFORMERS

In one instance I thought the hum was my guitar; it turned out instead to be the wall wart (AC Converter) that fed my Roland MicroCube.  How did I find out?  I unplugged it and ran the cube on batteries and the hum vanished.  Another way would be to try other wall warts and see if they do better (once I went through six wall warts until I found one that worked properly.   They are notoriously poor in manufacture). 

 

TEST THE AMP-  STANDARD

Try a different amp if you have one and see if the hum disappears.  If hum vanishes, you just located the source without much trouble.  Internal wiring is out of my ability to trace without risk of painful or fatal electrical incident.  In such case I usually just acquire a new amp.  If your amp is pricey, repair may be the only option to stopping the hum.  Again, this is if your current amp hums and a replacement amp doesn't; that pretty much pinpoints the hum source.

 

TEST THE INSTRUMENT

Test two or three guitars if you have them and see if the hum remains, vanishes, or changes.  If the hum remains across all gits, then that almost insures the problem is either with the amp or the environment (unless of course, you have 2 or 3 problem gits-- not likely).  If it's the instrument, see below on how to correct that problem.

 

TEST LOCATION / ENVIRONMENT

If hum persists, eliminate the environment as a possibility.  Hum could be caused by something in your home or workshop.  Entire houses or even city blocks can have unstable electric flow, causing hum in the lines.

Is the problem an ungrounded outlet?  Use a 3-prong outlet ground tester to make sure the outlet is grounded (available almost anywhere).  If all shows green you're good to go.  If it shows ungrounded, you'll need to ground your outlet-- or switch to another outlet that is grounded.

If your outlet is grounded, take the git and amp to another location and see if you still experience hum.   First move to other rooms and test the system.  If the hum persists move to another place entirely... a local park with electric outlet or someplace totally away from your home area where you can test your guitar and amp.  If the problem is in your home... an entire area of the city up to the central transformer could potentially be affected.  Eliminate the environment as a cause.  If you go elsewhere and the hum disappears, you'll either need to just get used to the hum or invest in a hum eliminator device or voltage regulator (plugs between your amp and wall socket to stabilize voltage and eliminate hum).

Do you have fluorescent lights?  Those little twisty bulbs?  Computer equipment nearby?  Heavy electronics nearby (microwave, television, etc).  Those are known sources of RFI (radio frequency interference).  You can try isolating your music setup from proximity to those,

 

HOW TO FIX A WONKY GIT

If the hum problem turns out to be your guitar... something isn't connected properly somewhere.  You'll want to make sure items that need to be grounded are connected to the negative (center) pole of your guitar jack-- either directly or through a central grounding wire.  If you don't understand guitar electronics, you may need to have it checked at your local music store.

* Pickups. "Humbuckers" are so named because the double-coils naturally inhibit hum.  If you're using a single-coil pickup (common with CBGs) the pickup itself could be the source of hum.   Google shield coil pickup for lots of information on eliminating pickup hum.

* Pickup cover.  Some pickup covers are metal and have to be grounded.  If they're not they can cause significant hum.  Solution:  ground to the pickup ground wire.

* Sound wiring.  Sometimes the instrument wiring is simply hooked up wrong.  Double and triple-check the wiring layout and see if all the wires are where they're supposed to be.  Is the guitar internal wiring grounded properly?

* Bridge Saddle.  Usually both tuning keys and strings are grounded through the bridge saddle, which itself is grounded through the bridge base.  Sometimes that grounding comes loose, or was never properly grounded in the first place.  If the strings don't touch metal you may need to add a metal strip to the tail or bridge and ground to the jack in order to ground the strings.  They're steel / nickel / chrome and are basically horizontal antennas... very sensitive to interference.  Make sure everything metal is grounded. 

* Fancy do-dad.   If you have a license plate or other metal decoration on your git that's any larger than a bottle cap, it could be picking up interference.  If there are metal decorations (especially license plate guitars), ground them. 

* Faulty pot grounding.   Sometimes a ground solder on a pot may look good but actually not be grounding correctly.   In other cases the pot itself is burned out and not grounding correctly.  In some cases the pot can be faulty right from the factory.  If you've tried everything else and it still hums, I recommend:

     a) Unsolder and re-solder all ground connections on the pot (being careful to not get the pot too hot.  Touch the iron to the solder, not the pot, and molten solder to the pot). 

     b) If it still hums after that, replace the pots one by one and see if one of them was faulty.

 

THE FINAL, LAST-DITCH OPTION

If you've done all of the above and hum still persists, yet it goes away when you touch the guitar cord jacket... procure for yourself a "grounding wrist band".  You can buy these online or at computer stores in the form of "anti-static wrist bands" or make one yourself out of a loop of flexible wire or mesh and a gator clip.  When playing, wrap it around your wrist or run under your shirt, then clip it to ground somewhere on the guitar.  That should solve the hum problem no matter where it's coming from. 

 

In my experience if you do all the above, chances are the hum is going to vanish at one point or another and your problem will be solved.  If not... what's why there is a part 2 in this series.  ; )

 

Click here to read part 2 of this series

 

--o--

 

 

Fixing Hum and Noise Problems Tags: hum noise

Note:  This article applies to 110 / 120v electrical sources common to the United States.  Higher voltage sources in other countries would need to refer to electronics specialists in their area.

 

There it is again... that annoying hum from your guitar amplifier.  What is causing that?  It seems to come and go.  Sometimes it's louder, sometimes softer.  Is it the guitar, the amp or something difficult to identify?

 

CAUSES OF HUM

There can be many reasons for hum or noise in a piece of equipment (listed here in order of "easiest to identify and correct"):

* Jack-related ground loop issues
* Electric line ground loop issues
* RFI / EMI (radio frequency or electromagnetic interference)
* Bad line power ("noisy" electricity)
* Bad instrument or amplifier
... and stuff that really is difficult to identify.  Fortunately the most common causes of amplifier noise are easy to identify and correct-- although it may cost you a bit to fix it.

 

JACK-RELATED GROUND LOOP ISSUE

    This is very easy to test.  Plug a regular guitar cord into your amp (but not into your instrument).   If you hear hum / noise, unplug the cord.  If the noise vanishes, you have a jack-related ground loop issue.

    Fixing this problem is reasonably low-cost (about $20 or so).  You will need to purchase an instrument/microphone ground loop eliminator.  Models are made by Pyle, Behringer and other music companies.  You plug your instrument cord into this device and then run another cord to your amplifier.  If the hum is instrument or cord related, this will very likely correct the majority of the problem.

   Note that this may not fix issues in which there is something wrong with the instrument (an internal short or grounding issue).  For that you'll need to have the instrument inspected and repaired.  But if you tested with a raw guitar cord and the problem disappears when the cord is unplugged from the amp, a jack ground loop eliminator will very likely be the solution.

ELECTRIC LINE GROUND LOOP ISSUES

   Testing for this issue is easy if your amplifier has a 3-prong electric cord.  (If your amp has a 2-prong cord, you can skip this section.)   Sometimes interference from "ground loop" causes noise problems (other items on the line). 

 

    IMPORTANT!  FOLLOW THESE INSTRUCTIONS FULLY!  To test for this use a common 3-prong to 2-prong adapter (a little plug you can find in almost any store).  If you plug the amp in using this adapter and the noise vanishes, you have an electric line ground loop issue.  Whether the hum vanishes or remains, once the test is performed (2 seconds or so), immediately turn off the amp and remove the test plug.  A 3-prong amp should never be operated with a 2-prong adapter for any length of time.  This is for testing purposes only.

    Resist the urge to keep using this easy and inexpensive device to fix the issue.  There is a reason your amp has 3 prongs; using a 2 prong adapter for a length of time can cause grounding issues and result in blowing out your amp or (worst scenario, however rare) starting a fire or severely shock the player.  Just don't do it.

    What you will need in this case is a power ground loop filter, which can take care of such problems.  It's not an inexpensive fix ($60 and up depending on your source) but it will most likely fix this electrical problem.  

 

RFI/EMI ISSUES

    Anyone who has ever lived near a radio or TV station or near a power generator will likely have experienced this kind of problem.  This can also happen in areas with florescent lights, heavy machinery, microwave ovens, computer equipment, large video monitors, or other sundry electrical equipment that can produce radio frequency or electro-magnetic interference.

    There are many solutions for such, depending on the source, direction and seriousness of the interference.  Shielded cables in your instrument and all cords (including the power cord) may be required.  Many guitars are already shielded from RFI/EMI, but many aren't.  You can shield them by opening the electronics area and lining it with aluminum or copper tape (available in electronics stores or online). 

    In the case of an amplifier an inelegant solution is to cover it with aluminum foil.  A slightly more elegant solution is to build a "Faraday Cage"-- which is basically a mesh-wire box to surround most of your amplifier.  Either method may block interference and allow your amp to work noise-free.  You will still need a good-quality shielded guitar cable and power cable.

    Note that these are measures for "extreme" situations of electrical interference.  Less-extreme is to try to locate the source of interference and increase the distance between that source and your music equipment.

 

NOISY ELECTRICITY

    Sometimes noise is caused by a bad electric line.  Basically the quality of electricity coming from your socket is unstable, causing erratic behavior.  In such instance the best option is to have an electrician come out and check your house, because such problem can shorten the life of all of your electric appliances.

    But for your instruments and amps there are several solutions.  The least expensive are voltage regulators or a standard UPS (uninterruptable power supply)-- basically a computer battery backup.  A voltage regulator tries to clean up your energy line and can smooth out your current.  A UPS puts a battery between your electricity and amplifier, which also acts as a voltage regulator.  A UPS is also the very best way to prevent electrical surges and even direct lightning strikes.  (There are recorded cases where the UPS was disabled or even melted down, preventing damage to other equipment.)  I personally have UPS devices on all of my sensitive electronic equipment.

    However, either of these devices may be insufficient for really bad line noise.  For such noise you may need a professional musician's line noise filter, which can run a hefty $200 or more.  There are many options in this area, so shop around and see what works in your case.  Starting with the inexpensive and work up if necessary.  Purchasing from a retailer that allows returns in case of failure might be a wise and low-cost solution.  If you can get by with a voltage regulator or UPS, that will be your least-expensive answer to this problem.

 

INSTRUMENT / AMPLIFIER ISSUES

    Both instruments and amplifiers degrade with age and need repaired or replaced.  Some items are simply built poorly or have a problem develop during the manufacturing process (a weak solder point, bad part, etc).   If you perform the basic tests listed above and the noise still persists, you may need to have your equipment tested for noise issues.

    This is most easily done through the process of elimination: keep replacing equipment (cords first, instruments, amplifiers) until you find the piece of faulty equipment.  Always test cords first; it's amazing how often a problem is simply a matter of a bad connector cord.

    An electric guitar can be tested by plugging a different electric guitar into the same amplifier, using the same cord, and seeing if the noise vanishes.  If it does, your guitar is the issue.

    An amplifier can be tested in the same manner.  Have a friend bring over his/her amplifier and test it in the same environment, same electric outlet, same guitar cord and instrument.   If the noise persists it's not likely to be the amplifier.  If it vanishes you'll have a good hint your amplifier needs repaired or replaced. 

 

SUMMARY

    Most causes of hum fall into four areas:  jack-related ground loop, electric source ground loop, RFI/EMI problems, equipment issues.   These can be tested and fixed at various degrees of expense.  Start by performing the easiest tests to isolate the source of the hum / noise and correct that source once it is found.

 

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