Counterintuitive retuning

[Sanson Corrasco]

When I leave my mandolin for a few days and come back to it, I always find it slightly sharp on the G, D, and E strings. The A sometimes, but not so often.

The mandolin stays in the same room with no great temperature or humidity variations all year round, AC in the summer and heat in the winter. The thing that puzzles me is this. I can imagine that the strings might be slowly stretching; I can imagine that the tuners might be slowly turning in reverse; I can imagine that the neck might slowly bow or that the top might slowly dish, but all of those things suggest that the instrument should go flat, not sharp. I can't think of any passive process where tension on the strings would increase.

Why do the strings go sharp?

[bolannta]

They cool down when no longer heated by contact with your fingers and contract?

[Loudloar]

Tuners don't turn by themselves. You can rule that out. The instrument can expand or contract with temperature changes, but you've said that the temperature stays consistent.

The likely cause is that the nut is pinching the G, D, and E strings. When you tighten the string to put it in tune there's a bit more tension on the tuner side of the nut because the string is sticking in the slot. Later the tension equalizes on both sides of the nut and the string has been pulled slightly sharp.

You can try lubricating the slot with pencil lead. If that doesn't help you may need to widen the slot just enough so the string moves freely. You don't want it too wide or the string will vibrate back and forth in the slot and cause a buzz. For wound strings also be sure the bottom of the slot is smooth. Sometimes the windings press a washboard texture into the bottom of the slot and the windings catch as you're tuning, then you hear it pop slightly as the windings move through the slot.

A qualified shop should be able to fix this easily. It helps to have the appropriate nut files, but it's possible to do it yourself using an inexpensive set of welding tip cleaners.

Steve

[Ivan Kelsall]

I have a similar problem with the bottom "A" string on my Weber Fern. I'll tune my mandolin up & a few minutes later the bottom "A" string will go sharp. I made an enquiry on here & this is what i was told (i was recently reminded of this by another 'Cafe member).
Divide the strings into 2 separate sections - 1) Above the nut - short bit. 2) Below the nut - long bit. Apparently,if the strings don't slide smoothly through the nut,as the strings 'stick',the string tension in the short bit can be higher than the tension in the long bit. If the string(s)then slip in the nut,the resulting 'equal tension' in the short/long bits can make the tension in the long bit higher than it was originally.
ie. - tension in short bit = 15 (whatever) / tension in long bit (in tune) = 10. That's for the un-equal pressure scenario. When the string slips & the tension equalises you'll get 10 + 15 divided by 2 = 12 1/2 in both sections.So the long bit becomes #.
Please - to all the mathematicians out there,that's just trying to put it in an ultra-simplistic way. I simply tune the lower "A" string a tad flat & it goes# to the right note,
Ivan

[G7MOF]

Are you sure the G D and E are sharp, and it's not the A string that's flat? lol

[Grommet]

If the mandolin is an archtop, and it were happening on the As as well, then I would surely suggest double checking for some increase in humidity. Maybe double check it anyway, As are wierd.

Scott

[Philphool]

Same thing happens to my mandos all the time. I can predict the weather by the tuning in the morning. (Ok, I'm exaggerating.)
My mandos stay in the same temperature controlled room, but even a small (~5%) change in humidity apparently changes the shape of the top enough to change the tuning. I wouldn't believe it if I hadn't seen it for years. Upside: I'm pretty good at tuning quickly now.

[Jon Hall]

From my experience, I think the condition of the strings will affect how long they stay in tune.

[Steve L]

My mandolins go sharp all the time.

[JeffD]

My mandolins go sharp in the spring and flat in the fall. I have always attributed this to changes in ambient humidity, of which even small variaions are significant.

[Ivan Kelsall]

Both my mandolins go sharp when they're cold & flat when they're warm.That's ALL the strings, not a few of them. Relative humidity in the UK is pretty stable,so i put it purely down to temp. causing expansion & contraction,
Ivan

[Bertram Henze]

They cool down when no longer heated by contact with your fingers and contract?

That points to what I think. To say the instrument stays in the same room is not necessarily true because the room is not the same with you in it. You can't smother your mandolin with steamy, sweaty hands and body heat, walk away and expect everything to stay the same

[Jimdalf]

If the string is sticking in the nut (sounds likely to me), I would go with the advice already given. To get past any changes that are likely to occur post-tuning, just pull the string away from the instrument a bit, this should pull the string through the nut and allow it to settle into the tension that it will stay at.

[Jim Nollman]

I had that same problem. I gave the mandolin to my luthier for 24 hours. He opened up the nut which solved it.

[Pete Summers]

When I leave my mandolin for a few days and come back to it, I always find it slightly sharp on the G, D, and E strings. The A sometimes, but not so often.

The mandolin stays in the same room with no great temperature or humidity variations all year round, AC in the summer and heat in the winter. The thing that puzzles me is this. I can imagine that the strings might be slowly stretching; I can imagine that the tuners might be slowly turning in reverse; I can imagine that the neck might slowly bow or that the top might slowly dish, but all of those things suggest that the instrument should go flat, not sharp. I can't think of any passive process where tension on the strings would increase.

Why do the strings go sharp?

Wood absorbs moisture from the air, swelling the wood of the mandolin top slightly, hence adding more tension to the strings, hence making them go sharp. Conversely, when the air dries out, the wood shrinks slightly, reducing tension on the strings, causing them to go flat. It happens to one degree or other to any wooden stringed instrument.

[Jim]

Mine go up & down with humidity. Odd that it would only go up. I would lube the nut to see if it makes a difference.

[Pete Summers]

Mine go up & down with humidity. Odd that it would only go up. I would lube the nut to see if it makes a difference.

That is odd. The OP doesn't say where he lives, but maybe it is humid all the time there?

[redietz]

My mandolins go sharp in the spring and flat in the fall. I have always attributed this to changes in ambient humidity, of which even small variaions are significant.

Yep. The OP says he heats in the winter, and uses A/C in the summer - I guarantee the humidity is changing.