Intonation problem with guitar

Question

I have a Fender Model CD-60 NAT, which is having some intonation problems. I fully intend to take it to a professional, but would like to understand the problem and the most likely fix beforehand.

• The action is pretty high. This is not the main problem.
• The problem is with the thin E string. When I tune the guitar wrt the open string, it plays just fine for the first three frets. See the harmonic minor scale shape I’ll be referring to:

The fret which has the first note of the scale, on the thick E string, will be called N. In the figure, N=8.

When I start with N=1, i.e. F harmonic minor, it’s fine. But the frets start getting progressively flatter and flatter (i.e, out of tune), so for eg. N=11, Eb harmonic minor, instead of the two frets on the thin E string being 10 and 11, I have to play frets 11 and 12 to complete the scale. So by the time I reach N=11, the frets have started sounding one WHOLE SEMITONE flat. However, the first three frets are still sounding fine!

• The natural harmonic on the thin E string, which should occur on the 12th fret, actually occurs on my guitar in the 13th fret, with the note sounding like an E.

Answer 1

What you describe is pretty standard for a bridge saddle that is placed too far from the nut (i.e. intonated too flat.) The intonation adjustment at the bridge has more effect on higher frets than lower frets. So, if your intonation is flat, the notes will get flatter and flatter as you go up the fretboard.

HOWEVER, having your intonation be off by an entire semitone is unusual. So, please check intonation on the E, B, and G strings with a tuner. If only the E string goes flat, then the bridge should look pretty strange- the bridge saddle contact point with the E string would have to be a full centimeter further than the B and G to cause this.

Answer 2

There are multiple sources for intonation problems on a guitar.

1. Misaligned frets (or frets with a bad profile). Of course, if your frets are off, you will have a hard time with intonation. This is not really fixable, but should not happen on good instrument.
2. Wrong bridge position. Almost all electric guitars have adjustable bridge riders which allows for taking this position back or forth to compensate this. Characteristic for this is that the further up you go the flatter you get (if the position is to low) or the sharper you get (if the position is too high).
3. Wrong nut position. If the nut is in the wrong position the first fret is wrong, resulting in bad intonation especially around the lowest frets. Theoretically adjustable, but usually requires more effort that simply adjusting the bridge riders, as most nuts are not adjustable.
4. Bad technique. Pressing the strings too hard or accidently bending the strings can make the strings go sharp.
5. Overall limitations of the design. With straight frets you cannot get each not in tune, so you need to live with not ever note being exactly in tune (there are compensated frets, but that is pretty much a niche thing).

In you case (the higher you go the flatter you get) this is a clear sign of number two, with the bridge rider of the e string being too low. Of course, each guitar has combination of these issues, so you cannot get your guitar exactly in tune. Common practise is to intonate the guitar in such a way that the intonation is correct on the twelfth fret. A good way to check this quickly is to compare the harmonic with the actual pitch on the twelfth fret (although this is not exact, since the harmonic at the twelfth fret is not an exact octave of the open string).

The intonation of the string is affected by other factors like tension, thickness and action (pressing the string raises the tension, increasing the pitch). So this intonation must be adjusted quite frequently, even if you simply choose to use a slightly different set of strings.

Adjusting the action will thus require an adjustment of intonation, so this is something that should be done after you’ve setup everything else.

Answer 3

All of the 12th fret harmonics should sound when the strings are touched exactly over the 12th fretwire. And should produce the same pitch as when the strings are pressed down on that 12th fret. That's called the intonation. When it's inaccurate, it's usually the bridge at fault, and with you producing that harmonic at the 13th fret, yes it's way out.

It's just possible that the string is at fault - the bridge does compensate for thicker strings by being placed further back for thicker strings - but top E is generally the shortest string of the lot. Change the string, maybe for a thinner gauge, oterwise it's major surgery, especially if the other 5 strings are intonated well. In fact, it's probably more than major surgery...