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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--

 

 

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