What’s the issue?

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TheLostArt
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What’s the issue?

Post by TheLostArt » September 21st, 2018, 1:58 am

Hello - I’ve joined this forum out of desperation and hoping someone can help!

I’m a full-time musician and mainly play a Martin DM acoustic for most of my gigs. It gets played a LOT. For example, I sometimes do cruise contracts which can mean playing it 4 times a day, every day for four months, so I had to get the frets dressed several times a year. When they became beyond saving, I had the frets replaced with those “gold” alloy ones that don’t wear as fast. (They’ve been great)

Obviously, I was having some intonation problems before I got the frets replaced last year, but I’ve noticed that one of the issues persisted: the high e and b strings are slightly sharp as soon as I fret them anywhere on the neck. The issue isn’t quite as noticeable with a fresh set but I have to tune those two strings slightly flat and then either use a capo or try to avoid playing them open. It’s very frustrating!

My usual guitar tech suggested it might be an issue with the bridge so we replaced it with one that was shaped to add some extra compensation for intonation. It didn’t change anything. My understanding is that if I can tune the string slightly flat and it sounds fine fretted anywhere but when played open, then the frets aren’t the problem, and after replacing the bridge, all that’s left is an issue with the nut. My guitar tech disagrees and when we replaced the bridge said “that’s as good as it’ll get”.

I messaged another local guitar tech that’s always too busy to work on my guitar in the short gaps I sometimes have between gigs (must be good if he has such a backlog right?) and he suggested I try some fresh strings. Needless to say, I found this advice unhelpful because I get through around 5 packs a month.

I’m not willing to accept that I either have to put up with a guitar that doesn’t tune up or throw it in the dump, so perhaps someone here has an idea? Thanks for any help you can give me.

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NoteBoat
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Re: What’s the issue?

Post by NoteBoat » September 22nd, 2018, 3:25 am

Pitch is determined by the string mass, tension, and length. Since you're not changing the mass or tension when you fret, the issue is with the string length - and that means it's a problem that originates at either at the bridge saddle or the nut.

When you tune the open string to pitch an fret, then your strings are slightly sharp. That means the frets are too close to the bridge in relation to the speaking length of the open string.

If you tune slightly flat at the open string, all the fretted notes are ok - and that tells me that the bridge can't be the problem. If your speaking length was too long because the bridge saddle was too far back you'd have a situation where if you tuned any fretted note to be accurate, the frets above that point would be progressively more flat, and the frets below that point progressively more sharp.

Which narrows the problem down to the nut. The starting point for the string vibration is too far back (towards the peghead) compared to where it should be. Either the fretboard side of the nut has worn down from use, or you've managed to chip it right at the nut slot on the fretboard side. My guess is wear, since it affects two strings.

Replace the nut and you should be fine.
Guitar teacher offering lessons in Plainfield IL

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NoteBoat
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Re: What’s the issue?

Post by NoteBoat » September 22nd, 2018, 3:32 am

Oh yeah... since you've changed out the bridge to give it more compensation, there's one more thing:

Either the problem was caused by BOTH the nut and the saddle, which is possible due to wear, or you've now got too much compensation at the saddle end.

The only way to check this is to get a really accurate tuner. Tune the string at the midpoint - the 12th fret - to be exactly in tune. Then check to see how the intonation is at the 7th and 17th frets. If they are both in tune, then the saddle did need to be replaced, and all you need is the nut. But if you find that the 7th fret is a hair flat and the 17th is a touch sharp, then you've got too much compensation, and you're also going to have to replace the saddle again.
Guitar teacher offering lessons in Plainfield IL

TheLostArt
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Re: What’s the issue?

Post by TheLostArt » September 22nd, 2018, 4:00 am

Thanks so much for this! You have confirmed my own suspicions.

The technicians I have been using over the last few years have been very reluctant to replace my nut, even though I've had some issues with it before. This time I'm just going to tell them that I want to pay them to fit a new nut and they can take the job or leave it.

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