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Common Wiring Faults in Guitars

Guitar buzzes when plugged in with any pickup selected.  Buzz is still present when touching the strings, but disappears when touching the metal cover of the jack plugged into the guitar.  Guitar otherwise works correctly.

Likely Cause:

Ground wire to the bridge is not making proper contact at the bridge or at the grounding point inside guitar.  The wire has either become disconnected at one end, is not making proper contact at the bridge due to insulating paint preventing conductivity, or is missing altogether.

Solution:

The easiest method to check for a break in the ground wire is to use a multimeter set to the Ohms function.  Touch one probe to the strings and the other probe to the shell of your jack.  If the ground wire is present you will get a near-zero reading on the meter (indicating zero ohms resistance between the two probes, or a short circuit).  If your multimeter has a beeper function you can use this to speed things up a bit.  If the meter does not show a short circuit with the two probes attached, or no beep is heard you will need to do some exploring to discover where the break is.  Using the multimeter check between the following points for conductivity:

  • Between the strings and the saddles;
  • Between the strings and the bridge baseplate;
  • For a Tune-o-matic style bridge, between the strings and bridge studs/posts;
  • For a Tune-o-matic style bridge, between the strings and the tailpiece;
  • For a Strat or Floyd-style tremolo, between the strings and the sustain block;
  • For a Strat or Floyd-style tremolo, between the strings and the spring claw;
  • Between the strings and the grounding point inside the guitar (typically the back of the volume pot).

Once the break is located it should simply be a matter of joining the two points together to correct the buzzing problem.  If the ground wire has simply come adrift from inside the control cavity it is just a case of re-soldering this wire back in place.  Usually it will be evident where the wire was originally connected to – there may be a small wire stub nearby.

Note that heavy paint coatings on some bridges can prevent the ground from making good contact.  If the ground wire is definitely run to the bridge and is soldered correctly to the internal grounding point, but there is still no conductivity between the strings and ground, it is likely that the paint coating is preventing the ground from being connected all the way to the strings.  The only way to get around this situation is to ensure that every metal part (saddles, baseplate, posts, studs, tailpiece etc) that the ground needs to pass through in order to get to the strings is directly in contact with each other.  This may mean you will have to disassemble the bridge and remove some of the paint coating between parts to ensure good contact is maintained.

 

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Guitar buzzes when plugged in with any pickup selected.  Buzz lessens when touching the strings, but does not go away completely.  Buzz may also be accompanied by squealing, static or radio station noise bleeding through in the background.  Guitar otherwise works correctly.

Likely Cause:

Insufficient shielding inside the guitar control cavity may allow unwanted external noise sources to contaminate the guitar signal, or if shielding is fitted the grounding to the shielding is poorly connected or disconnected completely.

Solution:

Similar to the bridge grounding wire, it is necessary to determine if any shielding inside the guitar is correctly connected to ground by checking for continuity with the multimeter.  Shielding inside the guitar may be copper or aluminium foil, a solid metal plate or black conductive paint.  In any case the shielding material needs to be connected to the guitars’ ground point to be effective, and the multimeter is again used to verify this connection.  Check for continuity between:

  • The guitar shielding material and the output jack shell;
  • The guitar shielding material and the grounding point inside the guitar (typically the back of the volume pot).

If an open circuit is found at these points (no beep or multimeter indicates “OL”) then the connection needs to be restored in order to correct the fault.  The connection of the shielding material to ground may be either a direct wire connection, or more commonly via the act of securing a metallic component that is already grounded to the shielding material (eg, the metallic shaft of the volume pot may be providing the ground connection to the shielding material when it is bolted to the guitars’ scratch plate).  Note that the resistance of black conductive paint can appear relatively high compared to a copper or aluminium foil shield, sometimes in excess of several hundred ohms, but should normally be sufficient to ensure silent operation of the guitar.

If the guitar does not have any shielding fitted inside the control cavity it may be necessary to add your own to combat the noise problem.  Self-adhesive copper or aluminium foil tape can be added to a control cavity relatively easily, or the cavity coated with conductive paint.  Fitting shielding material is beyond the scope of this article, but there are several resources available on the internet that describes this process. Some general tips however may be pertinent:

  • You may find that sufficient noise reduction is obtained by just applying shielding to the surface that the controls are mounted to, rather than the entirety of the cavity.
  • If several pieces of conductive tape need to be used to cover the cavity ensure that every piece overlaps the next and that continuity can be measured between each piece.
  • Whatever method is used to shield the guitar, always ensure that it is grounded securely (eg, via the volume pots’ case or output jack nut) and is unlikely to become disconnected by vibration or general use.

 

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Guitar buzzes badly when plugged in with any pickup selected.  Buzz is not affected by touching the strings or any metal part.  If the volume pot is increased from zero the buzz quickly rises in intensity for the first three-quarters of rotation and then lessens slightly at maximum volume. Guitar otherwise works correctly.

Likely Cause:

Leads to output jack are wired back-to-front.

Solution:

There are two wires that are required to be connected to the output jack in order for the guitar to output a signal to an amp.  The ground wire goes to the sleeve tab of the jack and the signal wire goes to the tip.  As several jack construction styles exist it can be easy to mistakenly connect the two wires to the wrong points.  However using a multimeter it is easy to confirm the connections on a jack socket by a process of elimination.

Take a guitar lead and plug one end into the jack socket and leave the other end disconnected.  If the jack is already wired up to the guitar, raise the volume pot(s) to maximum.  Apply one multimeter probe to the sleeve of the disconnected-end of the guitar lead and apply the other to the ground wire soldered to the jack.  If the jack is wired correctly the multimeter will indicate a dead short.  If the jack is wired back-to-front the multimeter will indicate a non-zero value, perhaps in the region of 7-15kOhms depending on the electronics fitted to the guitar.  The same test can be applied to checking the tip (guitar signal) connections of the lead and jack.  Measure between the tip of the guitar lead and the signal wire soldered to the jack.  Continuity should be obtained between the two points if the jack is wired correctly.

 

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Volume pot has minimal effect when wound from fully up to fully off, and may also introduce a darkening of the guitar tone as it is wound to zero.

Likely Cause:

Ground connection is missing from one of the volume pot’s lugs.

Solution:

A volume pot works by variably sending a proportion of the pickup signal to the output, and requires three connections in order to work correctly.  Normally the incoming signal from the pickup(s) is wired to one side of the pot, the middle wiper is used to select how much signal is sent out, and the other side of the pot is wired to ground.  An alternative arrangement is to have the first two terminals reversed, and use the variable element to ‘send’ more or less pickup signal to the output (or the ‘top’ of the pot, if you like).

In a nutshell, the overall signal from the pickup is variably split between ‘full throttle’ at one end of the pots’ travel, and ‘totally off’ at the other end.

If the ground connection is missing the signal can no longer be split variably, and the pot simply acts as an extra resistance in series with the pickup signal.  The pickup signal can now only be ‘on’ or ‘slightly less on’.

Diagnosing may be as simple as looking for a wire that has come away from the pot and re-soldering it in place.  It may well look obvious which wire has become detached from the pot.

If using a multimeter, set to ohms function.  Plug a lead into the guitar, touch one probe to the shell of the lead and one to one of the outer terminals of the volume pot.  If the ground connection to the pot is working you will have a short circuit between jack shell and one volume pot lug.  NB, it is common to find that one pot lug is bent backwards and soldered onto the case, and many other ground connections within the guitar are also made to this point.  In this case it is wise to check for a short circuit from jack shell to the back of the volume pot, and also between the back of the pot and the bent-over lug.


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