Ohana SK-25z Intonation Issue

I picked up a used Ohana SK-25z a few weeks back and have been playing it quite a bit. When I first checked the Uke, the intonation was perfect. Last night I noticed that it just didn't sound right. All strings are in tune but when I start to check the notes lower on the fretboard I noticed that the C string has an issue at frets 2-4. It seems to go sharp for those four notes and then it seems to settle back in tune the lower I go. It's very strange but I have been bending that string on fret 3 for a week or so with a little riff.

So my question is this. By bending the note at fret 3, have I created a bad string?

I have not changed the original strings because the previous owner put Worth clears on it and I do like them. But I am sensing it's time to order some new ones.

Thoughts?

Kurt

The main reason for a string pulling sharp over the low-number frets is nut too high. When the nut slot is too shallow the string is made to stretch making it pull sharp.
This is usually more of a problem with steel strings than 'nylon', which are much more "stretchy" for any pitch rise.

You say that it was perfectly intonated before or is this something you have just noticed?

Do check the gap above first fret before doing anything, and come back on that.
If that gap is too small it will buzz on the first frets. It needs to be much bigger than say, on a steel-strung guitar.

Check the nut is seated and nothing caught in the slot lifting the string out of its slot.

Filing a nut is not difficult but it is a learnt skill, chances are first attempt will go badly wrong.

You should change the strings before messing with the nut. Clean the nut slots whilst you are doing that. Let the strings bed in before making any decisions about the nut. I never fettle a nut on brand new strings, they're too unstable.

Do not go rushing into filing the nut. Let's examine what else is going on here. How high is the action? Is the overall intonation (scale length) correct?

Actually, filing the nut slots to lower the nut action is quite easy if you have the right tools.
Here is what I got:
1) a rotary kit (with 80 pieces) for my ukulele building project, cost about 30$
2) in this kit, there are a few pieces that can be used as nut slot file (inexpensive one), their diameter is about right too.
3) a set of steel gauges (4$) that I used to check and set the action (this set ALONE would do, no need for the rotary kit above)
With these few simple tools:
a) find the steel gauge that is just a tiny bit higher than fret#1
b) slide that steel gauge against the nut, then file the slots lower, the gauge prevents from filing too deep and screw up the nut
JUST THAT SIMPLE. This works every time.
Someone also suggested an idea of using the diamond file to file "teeth" in a few steel gauge in the set above and use them as nut slot files. This also work well for me.

You have to lower the nut action and fret#12 action to your liking before checking intonation.
Most ukuleles I tested are sharp at fret#12 and I have an easy fix for it.
I just did that to my brand new nylon string guitar which has bad intonation at fret#12 (almost 1/4 note sharp).
After the fix, nearly right on.

Just change the strings before you start hacking at the instrument. Remember that some strings are very soft and will stretch very easily, so don't go tugging at them to get them in tune more quickly. I have known people with the same problem as you and they replaced the string three times or more before they heeded my advice. The problem is that they tugged at each string in exactly the same way, thinning it and sending it out of tune at a certain spot on the string. This is the most common "intonation problem" on the uke.

Thanks for the replies. I just ordered a couple sets of strings to try before making any changes. The intonation was perfect when I first received the Uke so it's a new problem. I was curious to see if anyone had had a similar problem.

Thanks Ken, I will remember not to stretch the new strings.

The one item I forgot to mention was the saddle. I noticed that the strings seemed a bit high and when I looked at the saddle I discovered a plastic spacer had been put under it. When I removed the sliver of plastic it looked like someone had wedged a piece of a credit card in there. Rather strange but once the sliver was taken out the strings were at a better height. Still higher than my Tenor but more to my liking. It's a straight saddle so I don't think there should be any compensating issues.

Kurt

Someone, either the manufacturer, the dealer, or the end user, raised the saddle, either because they liked a higher action or the strings were buzzing or the intonation was off or they had an irresistible urge to fiddle. You might find that you like it with the new, lower action or it might develop problems. I would press on and fix the uke with the new lower action, if you can. I agree that new strings are the first thing to try.

Well the idea on a beginner filing nut slots fills me with horror.

I've been doing this for a long while and I've seen what beginners do, with all kind of diy tools. Don't forget I was a beginner once too.

The correct tool is a nut file.
It makes the correct shape slot. Nut files are very expensive.

The ukulele uses nylon strings which are quite fat.
In a set of Swiss needle files there is one with a leaf pattern, curved on both sides. This one is not narrow enough for steel strings but will work for the narrow strings on a ukulele or classical guitar. There is another Swiss file in the set that is oval, this one will manage thicker strings such as those on a bass guitar.

The beginner will usually (read always) go too deep and ruin the nut. One pass too many with the file is too deep.

When you play the uke quite hard the strings excursion takes them quite a long way. If the slots are too deep then the string will connect with the first few frets. It is hard to judge how far to go. You have to play the instrument and take a little off and then play it again. The usual rule on a guitar or banjo or bass is the slots are the same height as the first fret, the strings pass over the 1st fret at the same height as they do over 2nd when fretted at first. Ime this is a little too low on the ukulele.
Also (NB) you must set the saddle height first because this lowers the strings too. Most new ukes I've seen have the saddle action too high and so they are sharp at 12th fret. Dropping the saddle and moving it back (tricky) sorts the intonation, but too low and the strings slap the fretboard. And every player is different.

Also the slot is sloped, actually it should be curved, so the string leaves the nut on its front edge and does not buzz over the headstock. This is easiest to do with a nut file, far easier than with a Swiss file of a floppy feeler gauge

I've made five or six nuts, they can be filed successfully if you go slowly and read about it first. I did go too low on one slot once but it was easily fixed.

But I agree - 1st try new strings, since the uke sounded OK before.

I also agree that you should get the action right at the saddle first, before you mess with the nut. The exception to this rule is if the intonation is horrible at the first fret but gets better as you go up the neck. In that case I suspect the nut is the main cause and consider attacking it first.

I bought some D'Addario J65 and T2 strings and they arrived yesterday. I put the T2 strings on and the intonation problem is gone. Looks like it was a simple string issue. Thanks for all the help.

Now the search to find the strings that work best with this uke..........

Kurt

Well the idea on a beginner filing nut slots fills me with horror

Click to expand...

there are two types of beginners: the ones who jump in without doing any research and the ones who carefully did their home work to really know what they will do.
Of course pro have the right tools to make a living, most of us are not pro.
I have done set up for more than a dozen mandolins and 3 or 4 ukuleles, 3 or 4 guitars, without any problem using just the simple tools I have.
Mandolins are much harder to deal with (due to their steel strings diameters).

And why "horror" ? the worst case is to replace a bad nut while learning a lot from mistakes.
It's not the end of the world like accidentally sitting on the fragile instrument.

Horror because I have seen and repaired such handiwork

But, no, you should learn how to file a nut.
It is not difficult but it is a practised skill, you do get better the more you do.

But I will say, if it is your first attempt, buy half a dozen new nut blanks and practice on them, not leap in and file the one and only nut on you instrument. It takes about that many to get the hang of it.

Proper nut files, which make the job a doddle, cost about £100 per set, ideally you need a set of straight (micro-saw) and tapered nut files. Plus a slitting saw, fine and ultra-fine wet'n'dry, engineer dividers, vernier callipers, Swiss files, carding files, small vise, engineers clamps, jeweller's rouge, glasses, loupe, nut blanks in several and various sizes and materials, and the ability to swear in several languages.
Otoh see my post above re Swiss needle files which /can/ be used for nylon thickness strings.

I have noticed that "nylon" stringed instruments like the nut a trifle higher than you would set it for steel strings, because string excursion seems to be greater with nylon strings.

If you file the nut slots down to "just right and no lower" and then drop the saddle, you will lower the strings at the nut too, just enough to cause annoying fret buzz at first.