Pesky B & G strings on Martin D-15M; am I diagnosing this right?

RoscoeElegante

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Hey, all. Hope this you well.

On my Martin D-15M, bought (very) used a few years ago, the B string:
-Slips flat almost randomly
-Doesn't want to tune well with the G string
-Has a faint, very tinny buzz when played open

Meanwhile, the G string:
-Holds tune well, but won't intonate well starting at the 4th fret. It too is a bit flat from there upward--enough to sour some chords pretty noticeably

Both strings are wound on their respective tuning pegs properly. This happens to new strings (once they've stretched out), old strings, all brands of string, etc. I use the same medium gauge on it that the prior owner had used, but don't recall if he'd mentioned any tuning/stability problems on it. I do remember that the guitar had these problems when I got it, but they seemed less pronounced then. Maybe because of a honeymoon period.

So is this a tuning key + nut problem re: the B string, and a nut problem re: the G string?

If so, is the solution just a new tuning key for the B string, plus a newly cut and installed nut?

Everything else seems fine. The bridge is solid, the sound is rich and crisp, etc.

I'd just bring it to our local luthier but that shop has changed owners and luthiers a lot recently, and I don't hear good things (yet, hopefully).

With the semester crashing to an end, I'll finally have time to get the gear running right....

Thanks for your advice.
 

NoTeleBob

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I think the first step is to clean up the nut slots and make sure they aren't hindering string movement. It sounds a lot like classic nut issues.

On the intonation issue for the G string, I'm wondering if your nut slots are not cut at the right height. If you hold down your strings at the third fret, there should be a very tiny amount of clearance between the first fret and the bottom of the string. Something on the order of .010 inches. That's around the diameter of an E string for an electric. You can use an old string as a gauge if you'd like.

To correct it, you can use a set of net files. But if those are too expensive (Philadelphia Luthier has them for about $60), you can get a set of welding tip cleaners at a place like Home Depot or Lowe's for about six dollars. They are useless for Serious nut work but they are fine for just cleaning up the nut slots so that the strings move properly or for making minor adjustments in slot height on a previously cut nut.

You should also lube the nut slots. If you have a pencil, the graphite can be used for that.
 
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Boreas

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I would start with just polishing the nut slots. Likely too tight on the offending strings. I like to use abrasive cord. Also inspect the nut relief and make sure you have some. Make sure the tuner is tight and not twisting, but I doubt it is the tuner. One way to tell is to move it to a different position.

Abrasive cord is fairly cheap and comes in many diameters:

2022-05-04_11h17_05.jpg
 

RoscoeElegante

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Thanks, NoTeleBob & Boreas! The guitar was quite filthy when I got it. I removed the strings and scraped off the fretboard gunk, polished the frets, lightly oiled the fretboard, etc. At the time, I also cleaned the nut slots, but not with an abrasive cord. With clean parts of old strings, I think. I'll focus on that more systematically ASAP.

But if nut slot cleaning doesn't solve this, what are the next steps? It's my always-in-open-D guitar, and we've got a few gigs down the road that have a lot of songs set that way.

Thanks!
 

Peegoo

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Machine heads don't slip. They either are working or they're completely broken.

In addition to the good advice above.

I'll add:

Lubricate the nut slots. A dab of Chapstik in the slot or a very teensy dot of gun oil applied to the string laying in the slot (wipe it dry after applying with the point of a toothpick; some of the oil will seep down around the string into the slot).

Make sure you're properly "stretching in" the strings when you install a new set.
- Install the strings and Tune all the strings so they're at proper pitch.
- With the guitar flat on your lap (table, workbench, etc.), hook your index finger under the low E string at the 12th fret and press your thumb to the fretboard. Using your thumb as a lever, lift up on the string so it's about an inch (no more than that) from the frets. Hold the string for a second or two, and let it back down. Check the tuning on the E string and make any necessary tuning adjustment with the headstock tuner. Repeat the string lift thing, and check tuning again. When the string holds tuning after a stretch, you're done.
- Move to the A string and repeat the stretch process, checking tuning after stretching. Do the same with all the strings.
- This business of gripping the string at several places along its length and stretching, like you see demonstrated all over the Web, is goofy. It's useless and does nothing different, because lifting the string as I described applies an equal, balanced amount of additional tension along the entire length of the string. No need to grab it in several places.

When tuning each string, always tune up to the note; never down. This prevents strings from going flat. If the string is sharp, lower its pitch below your target pitch and tune up to the desired note.
 

NoTeleBob

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[snip]
When tuning each string, always tune up to the note; never down. This prevents strings from going flat. If the string is sharp, lower its pitch below your target pitch and tune up to the desired note.

Definitely this. Even if you need to drop just a tinge, drop a little more, come back up to it.

I like @Peegoo 's method for stretching, but I'd drop the amount of pull on the thin strings. I used to do it that way and I broke a few. I've changed to doing a serious bend a few times. I bend as far as my most extreme bend. I figure that way I won't push them any further than they'd 'normally' go. Do some bending, retune, repeat. Usually takes three cycles. Sometimes you get a little more stretch here and there as you play them in but it's soon gone.
 

philosofriend

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The G string going flat in the higher frets is caused by the saddle. With a one-piece straight saddle there will always be intonation issues somewhere. The only cure is to rework the bridge to take a two piece saddle (or a very wide saddle with its top intricately carved). I did this to one of my acoustics years ago and it turned the guitar into a whole different game in the high frets. The job took me about three hours and I learned not to use a router on an acoustic guitar bridge, even with ear protection it is deafening.

I'll bet your two plain strings intonate fine, the G is flat, the D is fine and the A and even more, the E are sharp. The bridge slot for the wound strings for a two piece saddle is cut closer to the headstock for the G and farther for the A and E.

There is no way the nut could be making the g string fret flat way up high.

Sticking nut slots is common on long unplayed guitars, especially if the strings were rusty or filthy. The "no tools" solution to crusty nut slots is to take a string of the same gauge that goes in that slot and pull it back and forth in the slot, trying to get it at the same angle that it goes in use. Do this dry first, then with pencil lead scrapings or whatever you like to lubricate.
 

Freeman Keller

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Good advice above. Another possible problem area is at the bridge. When you restring if the ball end of the string isn't tight against the bridge plate it can move as you tension the string. Often the pin pushes the the ball away from the bridge plate. I like to take a quick look inside with an inspection mirror after I put new strings on.

As far as intonation issues with the G string. The G has the smallest core wire of all of the strings and needs the least amount of compensation. If it plays flat then it is over compensated - the fix is a new nut properly compensated.
 

schmee

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Nut slots can be a culprit. They cant be tight. A little big is not an issue.
But I had one guitar that the B string would always be flat when I picked it up after sitting. Never did figure out why. The tuner seemed tight. The slot want any apparent issue.... it did this for years.
 

Thebluesman

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Hey, all. Hope this you well.

On my Martin D-15M, bought (very) used a few years ago, the B string:
-Slips flat almost randomly
-Doesn't want to tune well with the G string
-Has a faint, very tinny buzz when played open

Meanwhile, the G string:
-Holds tune well, but won't intonate well starting at the 4th fret. It too is a bit flat from there upward--enough to sour some chords pretty noticeably

Both strings are wound on their respective tuning pegs properly. This happens to new strings (once they've stretched out), old strings, all brands of string, etc. I use the same medium gauge on it that the prior owner had used, but don't recall if he'd mentioned any tuning/stability problems on it. I do remember that the guitar had these problems when I got it, but they seemed less pronounced then. Maybe because of a honeymoon period.

So is this a tuning key + nut problem re: the B string, and a nut problem re: the G string?

If so, is the solution just a new tuning key for the B string, plus a newly cut and installed nut?

Everything else seems fine. The bridge is solid, the sound is rich and crisp, etc.

I'd just bring it to our local luthier but that shop has changed owners and luthiers a lot recently, and I don't hear good things (yet, hopefully).

With the semester crashing to an end, I'll finally have time to get the gear running right....

Thanks for your advice.
issue is the particular string slots width requires widening by a few thou ..to now accept the strings diameter.,otherwise the string itself is being gripped by the 2 side walls .when string at tension now fretted,it will suddeny 'release itself' hence the sudden de tuning of the string=[drops] in pitch.once nut issue resolved=string can be tuned without issue.
combined-the strings tone will also be impeded =the buzzy sound.,because of the side walls gripping the string...=string bind.
widening the slot by a few thou to now accept the string correctly,resolves both issues simultaneously.
 

Thebluesman

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the string at pitch,when now fretted suddenly drops in pitch.the strings tone will also suffer=string bind.resolved by widening the string slot itself by a few thou.
sometimes a click is heard when string now fretted/suddenly drops in its pitch.=string bind.
can occur when string is being tuned to pitch too.[it is not tuner issue]
caution-one must avoid unintentionally deepening the string slot=it affects the action.simply widen it etc..to accept the strings diameter.
 

Thebluesman

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2 issues-1 is string bind.rectified at the nut.
2nd is the saddle=intonation issue there.rectified by replace saddle.

the string exits at the nut slot .it must not leave before the exit point is reached.if it does it will affect the strings specific scale length,governed at the nut and..at the saddle peak itself =intonation.If issues are traced to be at both nut+saddle=String will not be able to be tuned to pitch with any precision.the now fretted notes will be either flat/sharp.
one can diy both[if inclined+tools etc ] or find another to rectify both issues =further additional cost etc.problem resolved.
 

JL_LI

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I’d start with the nut. The description of the problem tells me that someone filed the nut on the B string angled up rather than down toward the headstock so the string rests on the headstock side of the slot rather than on the fretboard side as it should. The G slot may have been filed flat. This is a common amateur error. Get a precut bone nut and have a luthier install it and cut the slots for your playing style. Acoustics are challenging. You’ll want the nut cut less deeply if you’re a strummer and less deeply than that if you’re a string banger. There’s no right or wrong but a professional luthier should be able to cut a nut to suit your playing style.
 




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