Weird intonation issues - nut location/slotting?

[jamesmafyew]

I've got a Mexican Fender '72 Tele Deluxe that's been pretty heavily customized, and tuned down to baritone B to B tuning. It's great in most respects, and has had a pro setup or two (with my tuning and string gauges in mind), including level/crown/polish and a ramp added in the upper frets. I usually keep an eye on intonation myself. In terms of feel/action it plays really nicely, and sounds fantastic. A while back I had the nut replaced with one of those Graphtech black nuts, and profiled to bring the string height down to where it should be. Haven't given much though to it in a while, since I don't tour with it.

Recently, I've noticed that I can't intonate the guitar properly. Basically, when the 12th fret and the open string are in tune with each other, the lower frets will be sharp and the upper frets will be flat. This is most prominent on the 2nd string (usually B, F# in my case), but other strings exhibit the behavior to some degree. If I intonate so that the lower frets are in tune, the upper frets are WAY flat, and vice versa. If I intonate to the upper frets, the lower frets are WAY sharp. I'm using a strobe tuner to do this and I've changed strings multiple times and even tried a few different gauges, and the behavior is still the same.

I can't find any info on this online, and I don't remember having this problem in the past, but I'm also not sure when it started. Is my nut in the wrong place? Poorly cut? Saddle problems? Neck shim (this guitar has the micro-tilt adjustment, which I've never touched but a tech may have)?

[jrfrond]

This sounds like a classic case of the nut slots being too high, because you need to apply extra pressure on the lower frets to pull the string down, pulling it sharp. But in the middle of the string, where it is the most flexible, there is no issue. I see it a lot.

Also if you have it set up for baritone tuning, you should be using pretty heavy strings, like 12-54 AT LEAST. if you are using 10-46 or less, you don't have enough string tension to support proper tuning and the lower note problem is exacerbated, even if the nut slots are the right height.

You need a professional to set that guitar up for that tuning and proper intonation. Proper nut height and string gauge is imperative. This is your problem, and nothing else.

[jamesmafyew]

Except that the string height at the first fret is exactly the same as the string height at the second fret when fretting the first fret. As far as I can tell, the nut slot heights are exactly where they should be; any lower and the open notes would be buzzing. And the notes are sharp not just at the 2nd fret, but at the 7th fret too. And then getting flatter as you go up the neck, in a very smooth gradient. The weird thing is that the action is fairly high too, which as I understand it should make the notes up the neck sharp, not flat. And the string gauges are .013-.059, and it's been set up multiple times by professionals.

It also wouldn't explain why the 12th fret is in tune, but the 17th fret is 7-10 cents flat.

[Steve Conner]

My PRS did something similar ever since I changed the strings from the stock 9s to 10s. I also prefer a higher action than what it came with stock. If I intonate it by the usual 12th fret procedure, the first few notes on the low E string are slightly out.

I never figured out what caused it, I just live with it. Maybe the heavier E string sits a little higher because it has a bigger bend radius over the nut.

[David Schwab]

Except that the string height at the first fret is exactly the same as the string height at the second fret when fretting the first fret.

The way I learned to check it is fret the string at the second fret, and the string should just clear the first fret.

Also check that the strings are actually breaking off the front edge of the nut, and make sire that some how the nut didn't move closer to the first fret somehow.

[jamesmafyew]

The way I learned to check it is fret the string at the second fret, and the string should just clear the first fret.

By this measure, the height looks perfect. But since the nut is black and the slots are pretty deep, I'm having a hard time telling whether the strings actually break at the front edge. If they broke further back, would that cause my issue? Say, for example, that the open string was flat relative all frets, but compensating to bring the scale so that the 12th fret lined up, then might half my frets be sharp and half flat?

I guess what I'm asking is should I take this thing to yet another guitar tech (getting hard to find around here) to get another nut put in, or should I be looking at other things on the guitar?

[dai h.]

My PRS did something similar ever since I changed the strings from the stock 9s to 10s. I also prefer a higher action than what it came with stock. If I intonate it by the usual 12th fret procedure, the first few notes on the low E string are slightly out.

I never figured out what caused it, I just live with it. Maybe the heavier E string sits a little higher because it has a bigger bend radius over the nut.

I remember reading (in GPlayer in response to Buzz Feiten system IIRC) that they (PRS) moved the nut slightly towards the bridge but did not advertise this. Something to do with that, possibly?

[Steve Conner]

I remember reading (in GPlayer in response to Buzz Feiten system IIRC) that they (PRS) moved the nut slightly towards the bridge but did not advertise this. Something to do with that, possibly?

Interesting!

Jamesmafyew, try grabbing hold of the string near the nut and wiggling it around. It should be obvious whether it's held firmly at the front of the nut slot.

Also, maybe you have way more relief in the neck than what it was designed for? The guitar fret placement math is built on the assumption that the extra tension introduced by pushing the string down to the fretboard is negligible.

With a high enough action (as you might reasonably want when playing a baritone guitar with heavy strings) that assumption becomes invalid.

If you then use the intonation adjustment to compensate this extra tension, the compensation only works at the 12th fret and gives a pitch error everywhere else.

Guitar tuning is a compromise, like so many other things. And modern tuners are very sensitive.

[David Schwab]

By this measure, the height looks perfect. But since the nut is black and the slots are pretty deep, I'm having a hard time telling whether the strings actually break at the front edge. If they broke further back, would that cause my issue?

If you were to move the break point farther from the first fret, the notes would be sharp, because the distance from the nut to the frets has increased, so it's like moving the frets closer to the bridge.

The Buzz Feiten system moves the nut edge .020" closer to the frets to slightly flatten the notes. This is because the strings are stiff at the anchoring points, so the harmonics are sharp.

[jamesmafyew]

Ah, ok, help me think through this then:

1. Nut is too far back, so all frets are sharp.

2. Compensate for this by moving the saddle back so that the 12th fret is in tune with the open string.

What happens now? We've just made the scale longer than the frets are spaced for... so the frets are in effect "too close together" -- wouldn't that mean that the frets below 12 would be sharp (too close to 12th fret for the scale) and frets above 12 would be flat (ditto)?

I think this may be my issue -- the nut was installed wrong somehow. Please point out the flaws in my logic! I'm not good at the guitar tech-ing stuff.

[David Schwab]

wouldn't that mean that the frets below 12 would be sharp (too close to 12th fret for the scale) and frets above 12 would be flat (ditto)?

If its not over done, no. That's how the Feiten system works. Because the notes are naturally sharp on the first few frets (assuming you aren't using a zero fret, which fixes the issue), then it all works out.

I've never had tuning issues with the low frets because I cut my nut low or use zero frets.

[Steve Conner]

Sure, but if it was overdone, wouldn't it produce symptoms like what jamesmafyew was complaining of? It seems logical to me.

I think I remember having similar problems when trying to set up a guitar with heavier strings and a higher action than it was designed for.

[jrfrond]

Well, this sounds like a weird one. This much I can say though: those necks are all cut on CNC machines, and the frets are cut on a gang saw (ie. all frets are cut at once with a 21-blade circular saw). It is almost impossible to have incorrect placement and/or scale length.

Do you have a lot of relief in the fingerboard? Too much relief can play a bit with intonation. In practice, it moves the nut slightly closer to the bridge. Try tuning your guitar to pitch and then tighten the truss rod. The pitch of the strings will go UP, because you are moving the headstock farther away. You are straightening out a curve. While the LINEAR measurement remains the same, the point-to-point measurement changes.

[jamesmafyew]

It did have quite a bit of relief...maybe .7-1.0mm at 7th fret with 1st and 15th depressed. Last night I tried tightening the truss rod, to see what would happen. It's pretty tight already so I didn't want to overdo it, went about 1/4-3/8 of a turn tighter. The problem got a LITTLE bit better, but it's still particularly apparent on the 2nd (normally B, F# in my case) string, less so on the others. I had to raise the action a hair to eliminate some buzzing after the adjustment.

Another tangent -- this guitar has one of those "micro-tilt" adjustments, which I've never touched, but may have been adjusted by a tech at some point. Is it possible that neck angle could cause something like this?

[imaradiostar]

How does it behave when capo'd?

Specifically- capo and tune it so that the first fret acts like a zero fret. See if it makes a difference. You can then compare intonation at the 2nd and 3rd frets and see if the problem persists. If not then I'd argue that the nut could be moved closer to the bridge to achieve a similar effect.

jamie