Intonation woes: First four frets on the low B.
Hello, denizens of TalkBass.
I'm experiencing a problem with my five string Uno that has stumped my local guitar tech. In short, the intonation is spot-on across the fretboard... except on the low C, C#, D, and D#, which are noticeably (i.e., about a semitone) sharp. That is to say, when tuned at the twelfth fret, all notes on the fretboard are in tune except for the first four frets on the low B string. Fifth fret upward is fine.
My own attempts to adjust the intonation at the bridge have, unsurprisingly, changed the rest of the notes for the worse. I've tested using a capo and ensuring that the string is straight when fretted, so my technique (while certainly not perfect) is not the source. I've changed the strings to a fresh, new set, and still no luck.
I've taken the bass to a tech to resolve the issue, and he basically said I'm SOL after two attempts to fix it. I asked if the problem could be rectified by filing the nut, leveling the frets, or adjusting the action. According to him, the answer to all three is "no".
I've done a search through this forum but have not seen a thread addressing this particular problem yet. Has anyone else experienced something akin to this, and/or has an idea of what may be causing it?
Is this a new bass or one you've had that was right and this happened after the strings were changed?
Make sure the witness points at the bridge and top nut are set. Press down with your thumb, or both thumbs, where the string bends over the bridge saddle and both sides of the top nut. This will reduce the height of the string from the frets which could be causing it to note sharp. If that doesn't help post again since there is the possibility you have a bad string or if the bass is new, the slot in the top nut needs to be filed lower.
Do you really mean they are sharp by a semitone? That's a whole fret.
If so, possibly the string is sitting way too parallel (too low when fretted) to the fret board
in that area.
So in fretting the 1st fret, the string is actually taking off from the 2nd fret, in fretting
the 2nd fret, the string is actually taking off from the 3rd fret, etc.
Try pressing extra hard at the problem frets. That will cause the string to lift slightly off
of the following frets. If the pitch drops, or it starts buzzing, then that would be the problem:
not enough "height over next fret".
The nut definitely needs to be looked at. If the nut slot is too low, then the string can buzz out on the next fret up. If it does it up a fret or two, then the bridge setup should be looked at. The neck should also be sighted to see if there is any backbow at that point. If the slot is too high or doesn't have a good "witness point," then the string will pull sharp. It may pull sharp, anyway. Try a new string. If this doesn't fix it, and then if a trip to a qualified luthier doesn't fix it, you might need a nut shim. Measure the distance from the crown (middle) of the 12th fret to the 13th fret. Double that measurement. That should be the distance from the crown of the 1st fret back to the nut. If the distance is greater than this number, then the nut is misplaced and needs to be attended to by either a nut shim, a compensated nut, or another trip to the luthier to have the end of the fretboard and the distance from the fret to the nut sorted out.
IME, if the notes are ringing true and are simply just sharp, it is very likely not a low nut issue. That issue typically manifests itself also in buzzing and quickly-decaying notes. The more likely is that the nut slot is either too high or the slot is not wide enough to accommodate the string. This causes the string to be stretch too much when pushed down to the fingerboard and thus play sharp.
Inspect the string carefully in the slot to insure that it is seated well. You may have to widen and/or deepen the slot slightly so that the string seats correctly. Be VERY careful if you attempt it yourself. You can't really undo it, and if you get it too deep, the string will buzz on the first fret(s).
It is a fairly common issue. If your tech did not at least review and confirm that the nut is not the problem, you probably need a new tech. You might also try a different string including a tapered core B. Sometimes they are easier to intonate.
I am all but certain it can be addressed with the nut and/or the string itself. If it were a true problem with the bass's fret layout, you'd have a the same problem (at least to some degree) on the other strings, and it would be progressive up and down the neck.
But if not and you have exhausted every possible issue, if you still are having problems, then you can compensate by changing the "mid point" of the intonation. Set the intonation so the low E (5th fret) or maybe the F# (7th) plays in tune when stopped rather than the typical 12th fret method. This will help those lower notes play in tune. It will also cause the higher notes to play flat. But, how often do you play the B string in the upper register? Of course you might on occasion, but compared to the lower notes (the ones most buy a fiver for in the first place) not so much. If you have no other recourse, it is your best option.
It is all too common for the action at the nut to be way too high, although it's uncommon for a nut to be so high that it's still causing problems at the 4th fret!
Lotsa solid suggestions so far. To paraphrase:
*Check the gap between the 1st fret and B string while depressing the string directly onto the 3rd fret. Should be .003-.005". Use a feeler gauge ($4 at Pep Boys). Avoid business cards, dollar bills, and rolling papers.
*Visually inspect the string / slot relationship. Does the string's full-thickness wrap pass through the slot en route to the tuner? Does the string sit firmly in the bottom of the "U". Does the string pass smoothly as you tune up, i.e not grabbing?
*Set your witness points on the leading (fingerboard side) aspect of both the nut and bridge.
Thank you all for your responses.
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