Odd problem with treble pairs

I had a one-man shop make a mandolin for me this fall. The mandolin has good bass, but the treble pairs are weaker than on my MD315. On closer inspection, the two strings of the A pair seem out of tune with each other as I play up the neck. The E strings are the same way, but not as jarring. (I've changed strings a few times with same results.)

I knew there were some nut and fret issues, so I had Mass Street music do a Plek job and make a new nut. That helped some issues, but didn't fix the subject problem.

Could the bridge be the problem? (This luthier makes his own bridges and I can imagine that I see some potential issues (but could be my imagination, lol).) I would have hoped that Mass Street would have noticed any issues with the bridge. The bridge would be involved with ALL notes, open or fretted, so not sure why it would be different as I play up the neck. Just running out of components that might be the problem.

Suggestions?

(As I'm writing this, I'm thinking about other factors. This mandolin does have taller frets than on my MD315 - could that be a factor? Maybe as I'm playing up the neck, the small distance between frets might have me pushing down in a different way with the two strings in the string pair being pushed down by different parts of the fingertip and the taller frets allowing the strings to be pushed down farther and to different degrees?)

I'd check to see if the E & A strings are actually leaving the very front edge of the saddle. If one slot has a tiny hump in it, then the strings in a pair could have a tiny difference in scale length.
I'd drag a thin file through the slots and make sure the highest part of the slot is at the very edge.

Taller frets might invite too much pressure but that would be kind of random in effect. If your pitch difference is consistently in one direction, the strings may be at different heights at the bridge, so that one is deflected more than the other when fretting. Look across the bridge at a low angle to check if the A pair is uneven in height. If it is more uneven than the other pairs it is a good bet to be the cause.

Nut issues will be noticed in the low frets only. Bridge issues will become apparent as you go up the neck.

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Originally Posted by Doug Brock

... Could the bridge be the problem? ...

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If the problem was at the nut and w/ the open pair in tune, I'd expect the worst intonation at the first fret, evening out as you go up the neck (as the % of difference in string length / pitch becomes smaller).
(Edit: Typing slowly; sorry to duplicate Tom's comment above.)

Since the issue is opposite, getting worse going up the neck, the bridge does become suspect. In the same manner that Philpool suggests checking the nut w/ a file, I'd look to the bridge as well. Inspecting the string notches for string wear / compression could be revealing, maybe w/ a touch of graphite in there.

BTW, I find that the highest-strength cheap reading glasses, usually 3.25, are a HUGE help in diagnosing such issues. Focusing at 4" or 5" from your eyeball reveals much, regardless of your inherent eyesight, or lack thereof!

I just ordered a Cumberland Acoustic bridge. Fingers crossed that it fixes this weird problem and that I am then fabulously happy with this mandolin and never crave a mandolin upgrade again! :)

Never? Good luck ;)

In addition to reading glasses, those smart phones we carry around are also excellent at magnifying things. Take a good in-focus close up photo, then look at the photo on your phone and zoom in on that some more.

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Originally Posted by BrianWilliam

Never? Good luck ;)

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Yeah, that part of the statement was totally tongue-in-cheek! :)

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Originally Posted by Canoedad

In addition to reading glasses, those smart phones we carry around are also excellent at magnifying things. Take a good in-focus close up photo, then look at the photo on your phone and zoom in on that some more.

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I do that all the time! :)

When the pairs (courses) of strings do not note in tune with one another, the possible problems are: -the strings -the nut -the bridge. It is not likely to be the frets.
by process of elimination you've ruled out the strings (you said you changed them more than once) and the nut (you had a new one made, hopefully done correctly), and that leaves the bridge. A new bridge may help, but someone (you?) could have fixed the existing one by adjusting (cutting) the bridge top for improved intonation. In fact, I seldom install a mandolin bridge of any kind without having to adjust the intonation at least slightly.

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Originally Posted by sunburst

A new bridge may help, but someone (you?) could have fixed the existing one by adjusting (cutting) the bridge top for improved intonation. In fact, I seldom install a mandolin bridge of any kind without having to adjust the intonation at least slightly.

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I thought about taking the mandolin back to Mass Street to have them check the bridge and maybe fix or replace it, but I just ordered a Cumberland Bridge. Not all that expensive and good reputation.

I'll likely have the new bridge in hand before I could even get out to Mass Street, and Mass Street's backlog for repairs is usually several weeks. If the problem is due to the bridge, I'm still not sure why Mass Street didn't find any issues with the bridge. I paid for a setup, with new nut and the Plek process - I would have thought the setup would have included a check of the bridge.

I do see some possible issues with the existing bridge, both in the contours of the top edges as well as with the depths of some slots, so I'm maintaining some optimism that this might finally fix the problem.