intonation issue

TimmyHawken

Hi everybody,

I am having an intonation issue with my Dupont MD50E and was hoping someone would be able to advise me on what to do about it. It seems to only occuring on the B and high E string, but more significantly on the B string. The pitch at the octive is really sharp compared to the open note. I have only started noticing it about maybe 2 months ago, and it might be my imagination but it seems to be getting worse. That leads me to believe that it has to do with humidity and I do my best with limited resources to keep it from getting to dry and vise versa but it is tough in Michigan.

Do you think that is the issue? other info that may be of use is that I have changed strings several times, and that doesnt seem to change it. I have a #2 dupont bridge, nothing seems out of whack with it. I have even adjusted the distance from the bridge and the twelth fret to see if it had any good/bad effect, to no real results.

thanks for any help

Tim

Craig Bumgarner

TimmyHawken wrote:

...... I have even adjusted the distance from the bridge and the twelth fret to see if it had any good/bad effect, to no real results.

If you didn't get results, you're not moving it enough. If you move it an eighth of an inch, you should hear a clear difference between the fretted note at the 12th and the harmonic. If fretted note is flat, move toward the head. If sharp, move toward the tailpiece. A quarter inch will be dramatic, but whatever is needed is what is needed. I had an MD-20 that required the bass side of the bridge to be almost a 1/4 above the mustache, just the way it is.

An MD-50 is a high quality instrument. It is unlikely there is anything wrong with it, just requires standard tweaking. Intonation changes with the weather, the type and age of strings and maybe the phases of the moon .

The nice thing about the Sel-Mac bridge is you can easily change it. Once you get the hang of it, you don't even have to loosen the strings. I tweak mine at least once a month.

Craig

TimmyHawken

the bridge I have, like most that I've seen, is angle in so that when it's perfectly between the mustaches, the bridge is closer to the ovtive at the high E. Do you recommend pushing just that end back so that the bridge is actually more perfectly verticle then?

I will give it a try tonight and report back, thanks for the tip!

Tim

Craig Bumgarner

TimmyHawken wrote:

the bridge I have, like most that I've seen, is angle in so that when it's perfectly between the mustaches, the bridge is closer to the ovtive at the high E. Do you recommend pushing just that end back so that the bridge is actually more perfectly verticle then?

I'm getting lost in the words you're using. The mustaches are installed by the builder where the intonation sounded good at the time. The "angle" the bridge makes to the mustaches or to the centerline of the guitar body are not important and will vary from time to time. What does matter is intonation and that can be altered by moving either or both sides (treble side and bass side) of the bridge closer to the octave or further away. I usually adjust both the bass and the treble ends, first one, then the other. Sometimes it takes a couple tries, but seldom more than 30 seconds.

Here is a picture of the MD-20 bridge I was talking about. Notice how the bridge is over an 1/8" closer to the octave than the mustaches, even more on the treble side. I'm sure the mustaches were right when built, but things change over time.

Bob Holo

Wow man, if that's the bridge placement you're using and it's still off - something's amiss. In general: 4 things:

1.) The higher your action, the farther back your bridge needs to be to compensate - so - if you're cranking it forward like that to bring things into tune, then the mustaches are misplaced or your action is too low. It should be 2.5mm-3mm at the 12th fret on the high e and 2.7mm-3.2mm at the 12th fret on the low e.

2.) The B string is always sharp relative to the other strings. If you have a good sense of pitch it'll drive you nuts. The solution is to get a bridge with a compensated b string.

3.) The G string is *slightly* flat relative to the other strings. It won't bother you unless you really have perfect pitch. (as in... if someone says "sing a A" you can sing it and bet your life that it's exactly 440 cycles/second)

4.) Don't set your intonation by comparing the fretted note to the harmonic because the harmonic is off by about 2c at 1/2 670mm. Get a decent tuner and compare the open string to the fretted note.

Other things can throw off intonation - too much neck relief - odd harmonics from comb filtering that comes from a neck that isn't stiff enough. Intonation is an odd beast. Generally Duponts are pretty darned good - better than most - except the B string is not compensated and the necks aren't quite stiff enough. Other than that's they're pretty bullet proof. But it's usually not too bad unless you're really really sensitive to intonation issues. Try getting a compensated bridge and then take any excess relief out of the neck and set the action to a reasonable level and then set the intonation by comparing the open string vs. the fretted string at the 12th. Unless you have ears like a digital tuner that should fix things for you. Remember, if the fretted note is too sharp... that means the distance between the fret and the bridge is too short so move the bridge back.


**edit** oops... I thought that was a pic of Tim's guitar. Ah well... I'll leave the post up as a general intonation primer any way. Sorry. -Bob.

bertone

Bob,

A couple of questions about your post - when you say "the harmonic is off by 2c at 1/2 670mm" what does that mean? Sharp, flat, and how much?

Also, do you know of a source for compensated bridges for Selmac guitars?

Thanks, John in NJ

TimmyHawken

Craig - Your suggestion improved thing a bit, although I wouldn't call it a perfect fix. My bridge is now pretty far off the mustaches, like yours in the picture but in the opposite direction. Thanks though, it works for the most part.

Bob - thanks for the info, I was always comparing open notes with fretted 12th string (w/o a tuner though) and I've never considered my ear to have "perfect pitch" but it's pretty noticably sharp. I too would be very interested in your suggestion as to where to get and which bridge to get that has a compensated b string.

Also, Bob, I would be curious of your thoughts as to why my Dupont somewhat suddenly had this issue, do you think it is just a weather/humidity issue? Is there a chance adding a shim may improve matters?

As always, thanks so much for the information and the quick response. The level of information and friendlyness on this forum is amazing, and unparalleled.

Tim

BluesBop Harry

TimmyHawken wrote:

where to get and which bridge to get that has a compensated b string.

Josh Hegg will make you one, check out the store of this site and look for a custom bridge.

TimmyHawken wrote:

Is there a chance adding a shim may improve matters?

I doubt it... since your guitar is sharp already, higher action will only make matters worse.
I also play a Dupont and depending on string life i have adjust the bridge to get better intonation about once a week or so. I'm using a lowered #2 bridge.
You can try lowering the action by using a #1 bridge and that might help, use new strings for the high E and B, that usually works for me.

Bob Holo

Hi gents, Enrique pretty much answered the first question so I'll hit the second one. If I understand it correctly, the harmonic is 2c sharp. I don't remember where I learned this (live long enough and you become a repository of information with no index or bibliography) but believe the Western scale was derived by Pythagoras who essentially noted that if you hit the second harmonic on any string it produces (what we now call) the 5th. Tune the string to the harmonic pitch and repeat and you get the 5th of that fundamental... basically working your way around the circle of fifths. Unfortunately, Pythagoras didn't have access to an Intellitouch Tuner handy - so he didn't notice that by the time he worked his way around the circle of fifths he was 24c sharp. As people started trying to figure out how to deal with this inconvenient little bit of physics, the concept of "Temperament" was born. The original work of Pythagoras was called the "Pythagorean Temperament" but there are others.... "Equal Temperament", "Meantone", "Just", and "Equal" Temperaments. Each has it's advantages and disadvantages though guitar players typically are most satisfied with "Just Temperament" because it matches the harmonic series of the I, IV, & V.

The reality check is that a "cent" is 1/1000 of an octave (actually, it's even less than that, but let's use round numbers) so 2c is two tenths of one percent sharp... not really noticeable. But, if you tune using harmonics, by the time you reach the high E string you're 10c sharp E to E and if you have reasonably good ears - you can hear that clearly - particularly if you already have some intonation issues on the guitar (and believe me, they all do to some degree... and I'm guessing you could get shot for converting your 1940's Selmer to a fanned fret guitar - though that system works beautifully and Ralph Novak is a heck of a nice guy and sharp as they come.)