Strange intonation issue with new strings

[Herrmann]

Hello there,
I have a strange issue since I have put new strings (Optima) on my beloved MD305. The A strings are not well in tune together, a weird intonation when I go up the fret. All the others strings are good.
What would cause this ? I didn't have this issue before with my Thomastik.

[Phil Goodson]

Are the Optima A strings wound? (not that that would necessarily make a difference)

[kurth83]

Things I can think of to check:
- strings seated well in nut, meaning same height, a badly cut nut can do some very strange things. If the new strings are heavier gauge this would focus suspicion here.
- same check at the bridge.
- technique, pressing one string harder.
- bad string.

[John Bertotti]

I had a goofy issue recently on a guitar and found the nut was ever so slightly back cut, gave me fits. My A on the Oldwave with TI's is off but moves progressively flatter while moving up the neck. I got some wood from a forum member here to redo a saddle but decided to just shim the front edge of the A course at the bridge. How does the intonation change on yours as you move up the neck? Or is it different between the two strings?

[Herrmann]

Yes they are wounded.
I will check the nut and the bridge.

[Herrmann]

How does the intonation change on yours as you move up the neck? Or is it different between the two strings?
It is flatter up the neck, but only on one string, this is the weird thing.

[John Bertotti]

It is flatter up the neck, but only on one string, this is the weird thing.

My guess would be bridge or nut slot, although it is possible to get a odd string I haven’t seen that happen myself.

[Bob Clark]

Yes they are wounded.
I will check the nut and the bridge.

Herrmann, are you saying that the 'a' strings are wound, and that when they are in tune open, one of them is in tune as you move up the neck and the other is not? If so, you likely have a defective string. This happens. It is not common, but it does happen. Do you have another set of the same strings on hand from which you can swap out an 'a' string to try?

Before I'd mess around with the nut or bridge too much, I would want to make sure it is not simply a bad string. Simplest solution first, and do no harm in the process.

[pops1]

I have had bad strings several times over the years. When I bought strings by the dozen, I have had a bad bunch in the dozen. Way more than one string.

[twaaang]

If your former Thomastik A-strings were plain, and your present A-strings are wound: that may be your problem since they have different scale-lengths (shorter for the wound ones). I don't remember the underlying physics, but I do remember having to custom-make a bridge saddle when I went from regular D'Addarios to flat-wounds.

The default pattern on a regular saddle (assuming wound G and D, plain A and E) as you proceed from low to high is long, shorter, longer, shorter -- the transition from wound D to plain A calls for a longer scale on the A; and for either wound or plain, the higher-pitched string needs a slightly shorter scale.

If you have a wound A-string instead, the low-to-high pattern is long, shorter, shorter, longer: as the wound strings progress to a higher pitch they need slightly shorter scales; and when you finally transition to a plain string the scale-length becomes slightly longer.

I went through this with switching to flat-wounds on my (former) Lyon and Healy, where the A-string was driving me nuts. Joe Cleary (of Campanella Strings) teamed with me to make string-by-string fine measurements of the optimal scale length. From the results we created a plus/minus chart of how much front-end to remove from a blank saddle, at appropriate points, to get correct compensation for the new strings. The outcome was fabulous. I'm sure he under-charged me. -- Paul

[Phil Goodson]

Thomastik A strings are wound.

IF intonation was fine with TIs, why would you suspect nut or saddle? Change the strings.

[Tom Wright]

It would be a vendor mistake, but I (at least once) have had a packaged set with mismatched gauges in a pair. A micrometer would be handy, or by feel check if the flat one has less tension.

[Herrmann]

The tests I have done : inverting the strings invert the issue, so the issue is definitly the string. I will buy another set and see.

[Bob Clark]

Hi Herrmann,

Good; that is the simplest fix. I have had this problem. There was one brand of which had some bad strings go out and I was unfortunate enough to encounter them twice. In each case, though, they made good on it. You might want to email the manufacturer to see whether they will send you a replacement string. I would guess that they will.

Best wishes,

Bob