Balancing output with a humbucker

Using a simple resistor to match a single coil with a humbucker

It's a classic combination: a humbucker in the neck and a single coil in the bridge, but it can be a real challenge to keep that single coil from sounding too thin in comparison.  The problem arises for three reasons:

1. humbuckers are naturally warmer and louder than single coils
2. at the neck the string vibrates farther than at the bridge causing more bass and volume
3. humbucker-equipped guitars usually come with 500K pots

The third reason is the one I'll be talking about first.  Typically humbuckers sound better with 500K pots and single coils sound better with 250K pots.  This is because single coils sound better with a little bit of the highs bled off to the ground, and humbuckers (being naturally dark) sound better wide open.  This Telecaster Custom (shown above) came with four 500K pots, one each for neck volume, neck tone, bridge volume and bridge tone.  This sounds fine for the humbucker but to give the bridge pickup a little more warmth we are going to use a resistor.  If you follow this link you'll find a wiring diagram for the American Telecaster HS.  Scroll down to the second page and you'll see two pots, a switch and a resistor leading from the hot lead of the bridge pickup to ground.  Scroll down to the third page and you'll see that these are 500K pots and a 270K resistor.  I didn't have a 270K resistor, so for the Telecaster Custom we are going to use a 220K in series with a 39K resistor to give us 259K.

I then covered the resistors with shrink tubing to prevent a short and soldered it between the ground and the first lug on the volume control where the hot lead for the bridge connects.  You can also see a high-pass filter soldered between the first and second lug of the volume control consisting of a .001 uF capacitor and a 150K resistor wired in parallel.

This gives you a more uniform blend of highs and lows when you turn down the volume control.  This trick works great on bridge and neck pickups and I use it on all of my guitars.

The final thing to do is adjust your pickup height.  You want your bridge pickup to be reasonably close to the strings without touching them.  Depress the first and sixth string at the last fret and raise the pickup until it is very close.  If the pickup sounds harsh and metallic then back off a touch.  The neck pickup should be adjusted all the way down to the pickguard and then raised until the volume of the two pickups is equal.

How does a truss rod work?

The truss rod makes adjusting the bow in your neck possible.  They can be found in all modern electric, acoustic, and bass guitars.  some vintage guitars didn't come with a truss rod, but that's ok, as long as the action is not too low or too high.

Strings put a lot of tension between the tuners and the bridge, so naturally the neck will bow a little under the force, a little bow in the neck is a good thing.  Unfortunately wood is prone to warping due to temperature and humidity changes and can bow too much causing high action or even back-bow making the action too low and causing fret-buzz. 

A truss rod is a metal rod that runs up the length of the neck under the fingerboard and has a nut at one end for adjustment.  There are many different types of truss rods but one of the most common is the twin-action truss rod shown below.  They make it possible to adjust for either bow or backbow.

The twin-action rod is two threaded rods connected to blocks at both ends.  At one end there is a nut for adjustment, if you turn the nut clockwise it shortens the bottom rod and forces the rod and the neck to bend backwards and correct bow.  If you turn the nut counter clockwise it lengthens the bottom rod and forces the neck and the rod to bend forwards and correct backbow.  Here is a picture of how the truss rod fits in a small channel routed in the neck under the fingerboard.

The other type of rod is a single-action rod that only corrects for bow in a neck.  This type of rod requires a curved truss rod channel.  The rod itself (shown in green) is curved and when you tighten the nut it forces the rod to try to straighten out, thus straightening out the neck and correcting for too much bow.

Generally to adjust a truss rod you need to make very slight adjustments at a time, you may not even see results for 24 hours after the adjustment is made.  Go slowly to avoid breaking your truss rod, it is a very expensive repair.

For more information on how to set up your guitar, see our setup blog entry.