Intonation question

[prairiewind]

Please bear with a rookie. I've got a Pacific Rim import, a Morgan Monroe MMS-2 F-style knock-off. To improve volume and tone, I made and fitted my own Red Henry type maple bridge. I compensated the bridge using measurements from my 1917 Gibson A-1.

Here's the problem. With the bridge in its current location, I've got perfect intonation across all four sets of strings as measured using the twelfth fret harmonics and an Intellitouch PT-2 tuner. However, when I play unisons in first position, e.g. fretted D on G and open D, the fretted note is sharp. On all unisons, the fretted note is sharp by the same amount (at least according to the tuner).

My preliminary diagnosis is that the frets must be mislocated. Am I missing something else? Is this a common problem with lower end mandolins? I'll be personally upgrading to something better in the next 6 months or so, but I plan to keep the MMS-2 for my son to play. I'm probably going to relocate the bridge to get the best performance in first position. If it helps your pondering, the neck relief is neutral, that is to say its flat at tension, and the action is set at 4/64s at the seventh fret. Any advice is appreciated.

[Chris Baird]

Don't intonate using harmonics. Fret the 12th when intonating and this will include string stretch into the compensation and bridge placement.

[Flowerpot]

I think he is fretting the 12th and comparing to the octave harmonic. That is the standard way to get bridge placement.

It's possible that the nut is too high; I'd check that. But that would usually make the first couple of frets note sharp, and by the 7th fret (unisons, as you say) the effect of a high nut should be pretty small. Now that I think about it, it sounds like like a poorly cut fingerboard or misplaced nut.

I would check that the front of the nut aligns with the end of the fingerboard, rather than farther toward the peghead. The symptoms you describe would be consistent with a nut being placed too far away from the 1st fret.

[fidlmaker]

An often overlooked intonation gotcha is the string height at the nut, particularly with new instruments. Manufacturers set the height above optimal to help insure that they don't get instruments back because of buzzing after they've been shipped into a different environment (temerature/humidity). If the string is substantially harder to fret at the first fret than at the second or third, the string height needs to be lowered at the nut. The extra string height at the nut will cause the first couple of frets to be distinctly sharp, the condition lessening as you get farther from the nut. Contrary to some common misinformation floating around out there, you won't lose tone or volume by lowering the strings at the nut. Lowering at the bridge is a different story.

As far as what the proper height at the nut is, there are alot of opinions and preferences. But if you fret at the first position and don't get any buzzing, look at the string height over the second fret and you'll start to get a sense of how low you can go (if everthing else is perfect). You can see the same principal at work when a capo is placed on the first or second fret of a guitar. For all practical purposes the capo causes the fret in front of it to become the new "nut".

I usually set up a mandolin with about 0.010" between the Es and the first fret, gradually increasing to no less that 0.015" between the Gs and the first fret. If the rest of the setup is good, you shouldn't have any buzzes. If you still have an intonation problem, then you've at least knocked down one of the more common causes and can move on to other possible causes.

Let us know how it all works out.

[prairiewind]

Thanks for the feedback. I was indeed using the twelfth fret harmonic without actually fretting the note. This is as described in Jack Tottle's Bluegrass Mandolin instructional. I don't have any problem fretting at the first fret, so I believe the string height at the nut is ok. I'll go ahead and move the bridge according to the results of fretting the note at twelve. It may be a day or so before I have a chance to do this. I have a class to teach tomorrow morning, and tonight is my preparation time. Many thanks for your help.

[Charlie Derrington]

Usually, if your two unison strings intonate differently, then the problem is probably that the strings are not "leaving" the nut or the bridge at the very edge of either. Make sure that the slots angle back towards the headstock (on the nut) and towards the tailpiece on the bridge. Make sure the last point of contact is the very leading edge of both. Betcha the problem will be solved.

Old strings or certain brands of strings may cause the same problem, but you have to make certain my first suggestion is done first before you can check for a string intonation problem.

Charlie

[prairiewind]

Thanks Charlie. I did think of that for the bridge. I left the nut as supplied by the manufacturer, so that may still be a problem. The thing I liked about the old Gibson bridge was the way they cut the compensation into the bridge. That's the way I did it. Instead of angling the compensation using a flat file, I cut a vertical slot using a 1/4-inch flat-bladed hand chisel. I kind of like the vertical face for keeping the compensation distance constant regardless of the depth of the cut for the string.

[misifus]

Thanks for the feedback. I was indeed using the twelfth fret harmonic without actually fretting the note. This is as described in Jack Tottle's Bluegrass Mandolin instructional.
Prairiewind, to use the twelfth fret to locate the bridge, you play the twelfth fret harmonic and compare it to the fretted twelfth fret note. If they are not the same, the bridge needs to be moved. If the fretted note is sharper than the harmonic, the bridge needs to move away from the fretboard. If flat, the opposite.

If you haven't compared the fretted note to the harmonic, you may not have the bridge in the right place. The harmonic and the open note will always be an octave apart.

-Raf

[prairiewind]

Thanks misifus. As my first post indicated, I am indeed a rookie. I'll use your method, and I'll adjust appropriately. The consistency of the results led me to believe that there was a solution to the problem; however a new fretboard for a Morgan Monroe was out of the question. As I play the old Gibson and the new Morgan Monroe on alternate days most times, it was becoming really frustrating hearing great ringing in-tune notes from the old Gibson and sour notes from the new MMS-2.

[Chris Baird]

The best way to set the bridge for intonation is to make sure the fretted 12th is exactly one octave above the open string. Don't through the harmonics into it as it is unneccasary and doesn't factor in as many variables. Ultimately perfect intonation is not possible and you can only set intonation off a certain fret range. The 12th fret is arbitrary in a sense as you could intonate off the 7th fret(a better choice for beggining players) or any other for that matter. The problem is that every fret stretches the string differently and you can only set intonation for one particular stretch. The higher the action the greater the discrepencies will be. Very low actions do not have this problem to a noticable degree.

[Bob DeVellis]

I've come across instrument swith this probelm. Two things to check are the bridge height and string gauge. Higher and heavier strings have to be stretched more to contact the frets. This can cause intonation problems, such that fretted notes are prgressively more sharp as you move up the neck. This won't happen on a top quality instrument unless the parameters are way off but seems more common on more modest instruments. I remember Richard Walz saying that inappropriate strings would never intonate correctly on a bowlback. At first, I thought he was wrong and that with proper bridge placement, it should work. He was right; I was wrong. I suspect that in your efforts to improve volume and tone, you've cranked the bridge up. See if lowering it back down solves the problem. Correct pitch does a lot for tone.

[JGWoods]

"Usually, if your two unison strings intonate differently, then the problem is probably that the strings are not "leaving" the nut or the bridge at the very edge of either. Make sure that the slots angle back towards the headstock (on the nut) and towards the tailpiece on the bridge. Make sure the last point of contact is the very leading edge of both. Betcha the problem will be solved..."


Charlie
Pure gold advice.
Thanks Charlie
jgwoods

[prairiewind]

After class was over today, I used Chris Baird's suggestion. I located the bridge fretting G and E at the twelfth fret, and all notes are now spot on. Unisons sound great, and notes are sweet up the neck. Thanks again to all. BTW, I don't really recommend the one-piece maple bridge to all. With Thomastik-Infeld strings, the MMS-2 sounds pretty good, but I think a quality instrument with bronze phosphor strings would sound pretty harsh or shrill.