Need help with intonation problem

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Spectrum90
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Need help with intonation problem

Post by Spectrum90 » October 20th, 2015, 2:28 pm

A little back story so you get all the details. I have a 1990 Charvel Spectrum, just recently replaced the licensed schaller floyd rose with a pro model directly from floyd rose. I did this mainly because most of the saddle mounts where stripped. After installing it and not being able to obtain proper intonation I broke down and took it to a technician. He smoothed out the frets and set up intonation as well as replacing the selector switch. Now when I got it back I seems there is one problem neither he or I could solve. The G string is sharp. No matter how far back you move the saddle it is impossible to intonate.
Here is where my question comes in. What if anything can I adjust to fix this? Is it a nut problem? Its not the neck I'm sure. It's so damn frustrating. If I play an A major on the 5th fret and it's in tune, then I play a d major on the 5th fret the g string is sharp.
Please any help is appreciated Ive pulled out to much hair overt this guitar and I want it to work so bad, it is the style and sound I want but it's almost unplayable the way it is now

bottomender
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Re: Need help with intonation problem

Post by bottomender » October 29th, 2015, 10:18 am

Sounds like it could be the nut pinching the string. get some graphite powder and apply it to the string slot and see if that helps. putting a string in the slot and sliding it back and forth sometimes helps as well.

NoteBoat
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Re: Need help with intonation problem

Post by NoteBoat » October 29th, 2015, 8:02 pm

I'm trying to think through this - if your 5th fret A major is in tune, you're playing a C# on the G string. But when you play a D major at the 5th fret, the G string (which is now playing a D note) is sharp.

This tells me the problem isn't saddle placement. If your open string is in tune, and your 6th fret, the C#, is also in tune, the 6th fret should be in the proper position in relation to the bridge. If you move the bridge so that both your open string and your 7th fret are in tune, your 6th fret MUST now be flat - because it's farther from the bridge than it should be!

I can think of a few possible reasons this could be happening to your guitar.

1. Your G string is bad.

The pitch a string makes is a function of three variables: tension, length, and mass. Your string is at a constant tension, since you're not tweaking the tuner between the two chords. The length of the string is fixed by the position of the frets - you're shortening the string as you move from the sixth fret (for the A chord) to the 7th fret (for the D chord). Assuming those frets are in the right places, the only variable left is mass. And that means the mass of the string between the nut and the 7th fret is LESS than it should be.

This is a common cause of intonation problems with old strings. As strings get played, they gain weight - oils from your fingers, dirt, oxygen molecules binding to the alloys all add mass on a microscopic level. The string gets heavier, so it gets lower in pitch, and at some point you notice and increase the tension. But it hasn't gained weight uniformly - the larger increases in mass will come where you've played the string more. So if you've mostly played in the first five or six frets and you're now fretting at the 7th fret for the D chord, you should have exactly 2/3 of the string length vibrating (the distance from that fret to the bridge), but you've now got less than 2/3 of the mass vibrating, because the extra mass is mostly behind the point where you're fretting.

It's possible, but rare, for the mass distribution to be uneven within a string even when it's new. QC isn't perfect, so the first step is to put on a new string, and then get the bridge saddle in the right place. To do that, compare the 12th fret fretted note to the 12th fret harmonic - they should be exactly the same. If the fretted note is sharp compared to the harmonic, the saddle needs to move back (away from the nut) and if it's flat it needs to move forward.

After eliminating the string as a cause, we're at

2. A fret is damaged.

Frets should contact the strings at the center of the fret crown. If a fret is nicked or dented, or was filed improperly, the contact point may be too close to the bridge,making that fret sharp. In extreme cases, a fret is too low to contact the string at all - if your 7th fret sounds just like your 8th, that's probably why.

3. Your neck isn't straight.

If the 7th fret is farther from the plane of the string than it should be, you're pressing the string farther to reach the fret - which stretches the string, increasing tension and raising pitch. This could be a minor issue solved with a truss rod adjustment, or a major one that needs neck planing.

4. The fret is in the wrong place.

This is extremely rare - I've seen it twice in about 40 years. But that's more than zero, so I can't rule it out. If all of the other frets are in tune, and you have new strings and a properly adjusted saddle, it's really the only thing that's left.
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guitaranswerguy
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Re: Need help with intonation problem

Post by guitaranswerguy » November 6th, 2015, 6:17 am

Well, NoteBoat pretty much covered everything I would've asked.

I'm curious, did the OP ever get their issue resolved? I love a good guitar mystery, but love seeing them solved even more :D
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