While related, keeping a guitar in tune and having a guitar play in tune up and down the neck are two different issues.
If you have a guitar that goes out of tune while you play it, you need to go back and read the previous repair article. If your guitar stays in tune but the chords sound out of tune as you further up the neck and closer to the body, this is the article for you. Having your guitar play in tune up and down the neck is generally referred to as intonation.

Let me start off by saying that No Guitar Will Play Perfectly In Tune EVER. The tempered system of tuning upon which guitar fret placement relies on is imperfect, but it’s the best we can do. The system was designed by J.S. Bach in 1717 and first demonstrated on his work “The Well Tempered Clavier”. Before Bach’s tempered tuning, fixed pitch instruments (keyboards, instruments with frets, etc.) were designed to play in one key at a time. If you needed to play in a different key, you’d use a different instrument or completely retune the one you had. Bach’s system redesigned the relationship between all of the notes so that the octaves in all keys would be an octave apart. In order for this to work, all of the notes in between the octaves had to be slightly out of tune. For folks with good ears, nothing played on a guitar or piano really sounds in tune.

That said, lets talk about intonation as it applies to your guitar. Basically, intonation is the process of setting all of the octaves on your guitar an octave apart, and eliminating some of the problems that may hinder this procedure.

Most guitars have a string length between the nut and bridge of between 24” and 26”. If you were playing the guitar, as a slide instrument and not depressing the strings to the frets, setting the intonation would be a simple matter of placing the bridge of the instrument at the prescribed scale length. Since most guitarists press the stings down to fret them, simply setting the bridge to the scale length won’t work. When you press a string down, you bend it sharp. The bridge of the guitar needs to be moved in such a way as to lengthen the string beyond the calculated scale length to compensate for this. The amount of compensation is a function of string gauge, string core diameter, height of the string above the fingerboard, and the player’s technique. Basically speaking, the larger the core diameter, the harder you press, and higher the string height, the greater compensation. 

Setting the intonation can be pretty easy or complex depending on how picky you are and the limitations of the design of your instrument. It is easiest to set intonation on electric guitars with  fully adjustable bridges, neck and pickups. It is most complex to do so on an acoustic without these features. Quick functional intonation settings can be accomplished by properly setting one set of octaves on each string, while those with good ears may want to set several sets of octave on each string and average the setting for optimal results. 

Before intonation can be properly set, all of your ducks need to be in order. In other words, no matter what you do with string length, your guitar won’t play in tune unless the neck is properly adjusted, the nut height is set so that the strings are the same height over the first fret as they are over the second fret when the strings are depressed on the first fret, and the pickups are far enough away from the strings so that their magnetic field doesn’t interfere with the 
vibration of the strings. If the frets on your guitar are worn or unlevel, this will also cause intonation discrepancies. All these items will be topics of future articles.

To properly set the intonation, you will need a good electronic tuner or a well trained ear and a tube amplifier. Most good guitar repair shops use strobe tuners by Peterson or Conn. These provide the best results, thought any quality electronic tuner should work.

Assuming the guitar is properly set up, you are now ready to set the intonation. 

1. Tune the guitar to concert pitch with the electronic tuner.

2. Play the low E and check it against the tuner to see that it is still correct. 

3. Play the octave E at the 12th fret on the low E string. If the tuner shows that it is sharp to concert pitch, you need to lengthen the string. On an electric with an adjustable bridge, this is probably a matter of moving the E string bridge saddle away from the neck. On an acoustic, it will require filing the saddle in the proper direction. If the string is flat at the octave, it needs to be shortened and the process is reversed.

That's about all for keeping your guitar in tune. I welcome any questions or comments.

Scott Freilich
guitars@topshelfmusic.com
 

As a guitar repairman, this is probably the most common question I'm asked.

Keeping a guitar in tune is different than having a guitar play in tune relative to itself and other instruments. While the topics are related, they are not the same. For today, we'll stick to methods for keeping your guitar from drifting out of tune while your playing it.

The most common cause of tuning instability is unstreched strings. Most playes give their strings a little stretch after installation. A little stretch after installation. In this case, a little is not enough. If you want your guitar to stay in tune, you need to stretch the strings until they don't go out of tune when you stretch them. This may involve stretching them up several half steps several times to get them to stabilize. When you can't get the strings to go out of tune no matter how hard you stretch them, they won't go out of tune under normal playing conditions.

If after stretching you find that your guitar still drifts out of tune while playing, then the cause is most likely a mechanical problem. Many of my customers come in and ask me to change a perfectly good set of tuning gears because their guitar goes out of tune. Nine out of 10 times, the gears are not at fault. Often the string installation proceedure is the culpret. If your guitar is not equipped with locking tuners or a locking nut, the strings need to be locked onto the tuners. Locking the string can be achived in the following manner: 

1. Turn the tuner so that the hole in the tuner is perpendicular to the neck.
2. Pull the string through the hole in the tuner from the inside of the headstock towards the outside of the headstock. Leave about 1.5" of slack string on the inside of the headstock.
3.Take the free end of the string and go around the back of the gear and underneath the portion of the string going through the hole in the tuner.Bend the free end of the string up and over the the portion of the string where it meets the hole in the gear. 
4. Now tighten the tuner, allowing the string to wrap in a neat row down towards the bottom of the headstock so that the porting of the string going towards the bridge exits the gear as close to the bottom of the tuner as possible.

If you install your strings using this method, you should eliminate the majority of the mechanical problems involved in keeping the guitar in tune.

The next most common mechanical cause of tuning instability is a poorly cut nut. The nut is the spacer at the top of the neck near the tuning gears. It is important to have the slots in the nut cut accurately; too tight and the strings get caught in the slots, too loose and shift position in the slot. Unless you have experience and a set of fret files, leave this adjustment to your repairman. It is also important to have a nut made out of good material. Some of the budget guitars I see have nut material that is soft enough to have the string dig into them. These should be changed to a material like graphite, bone, micarta, or corian.

Keeping a guitar with a vibrato unit in tune involves a whole new set of mechanical problems. First and foremost, you need to use the vibrato within the limits of it's design. A Bigsby style vibrato or the units found on most vintage Fenders will not do dive bombs and stay in tune. A Bigsby requires a roller bridge or one that rocks in back and forth when the unit is used. A Fender Stratocaster or similar vibrato requires careful adjustment of the spring tension and mounting screws to have it return to pitch. Many of these also have a "tremsetter" stabilized installed with the springs which also requires adjustment. These are best left to the experienced repairman.

A locking vibrato can also cause mechanically related tuning problems. In addition to requireing adjustments similar to that of a vintage Fender, a loose or worn lock nut will cause the strings to slip out of tune. Check the attachment between the lock nut and the neck to make sure that it is solid. Also look at the locking plates to make sure that they don't have grooves worn into them from repeated use. If so, the lock nut will need to be replaced.

While acoustic guitars may share the nut and string installation problems, they have their own set of mechanical malidays. Most of these involve the bridge.

From repeated use, bridge pins and bridge pin holes become warn. Contrary to popular beleif, it's not really the pins that hold the strings on the guitar. the pins are installed to wedge the ball ends of the strings forward and onto a bridgeplate fastened to the underside of the top of the guitar. If the ball ends are not firmly seated against this plate, or if the plate is worn, the guitar will not stay in tune. Bridge pins that are too tight will not allow the ball ends to seat properly, and those that are too lose or warn will not push the ball ends forward onto the bridge plate. Pins are easy to replace and come in a multitude of styles. A worn bridgeplate requires repair or replacement.

That's about all for keeping your guitar in tune. I welcome any questions or comments.

Scott Freilich
guitars@topshelfmusic.com