Jazz Guitar Discussion
Joined: 14 Sep 2006
Location: Eureka, CA
|Posted: Sun Oct 25, 2009 6:15 pm Post subject: Setting Up A Guitar - Part 2
|I believe that the reasons for setup/adjustment/maintenance are well understood but briefly reviewing: we need to apply compensation to fragile wooden structures that have temperature stability and moisture absorption characteristics that are less than optimum (but have sonic characteristics that we value).
Additionally, stresses are frequently imposed on these structures for which they were not – or cannot be – designed to withstand, without dimensional change. Think of the jazz guitar as being a flexible structure, requiring a more frequent adjustment than a very rigid, solid-body guitar, protected by thick coatings of ultra-strong polyurethane.
In Part 1, we established an efficient method for measuring neck relief (clearance, action, and so forth). We can use the measurements obtained in this way to evaluate adjustments that we make to our instrument. Guitar setup usually goes something like this:
Define what is to be accomplished by the setup/adjustment.
Establish the baseline configuration by measurement.
Make the first set of adjustments.
Allow guitar to achieve dimensional stability.
Decide if performance goals have been achieved – by measurement or subjectively.
Iterate, if required.
Looks simple enough but this process can almost be open-ended/ongoing, especially considering seasonal changes, if one owns an instrument that is made from “green” wood or has manufacturing inconsistencies. In my experience, quality instruments will require only “maintenance” of the setup configuration once a satisfactory initial baseline has been achieved. Instruments of lesser quality may need some fiddly work on a frequent basis if they are to perform continuously at reasonably high standards.
Defining the goal, what do we hope to accomplish ? This is a “fuzzy” area and it may sometimes be helpful to actually write down our goal(s). First, because we may need to clarify our thinking on the subject (determine what we really want/need) but also because the order in which we perform adjustments might depend on what we want to achieve if, for example, modifications are to be performed too. Some typical goals might be:
Play “easier”, “raise or lower the action”, stop string “buzzing” and so on
Adjust “simple” intonation (making open string harmonic frequency = octave frequency)
Improve intonation over a broad range (difficult/time consuming)
Generally, the variables that we adjust during setup are the nut, the truss rod and the bridge. (Once properly set up, seasonal maintenance should require little more than slight bridge adjustments.) No alignment should be attempted before verifying that the nut is properly adjusted for the strings anticipated to be used. (This just means that the individual strings have the correct clearance over the first fret.) If you think that you must make this adjustment, it’s wise to anticipate problems by buying one or two unfinished nuts. They are inexpensive and available from many distributors - easily located with a routine internet search.
Strings should have just enough clearance over the first fret so that they don’t “buzz” when playing open chord configurations or open strings. Many (most ?) sources advocate a clearance of around .005 inches and that seems adequate to me. I certainly wouldn’t make the clearance any greater and, in fact, might try for a smaller gap. It’s HARD to make strings buzz against the “F” fret, they just don’t vibrate much so low on the neck. BUT because strings don’t readily buzz on the first fret, an implication is that the nut adjustment is finicky to get a tight clearance without buzz – and it is.
Recall when working on the nut, that the nut broadly affects the guitar’s performance, most especially in the area of the first five or six frets. Poorly adjusted nuts make a contribution to intonation difficulties and “action” or “feel”.
Nut adjustment is easily made with a set of so-called “jeweler’s files”. These are tiny files in various configurations in a packaged set, available from all normal tool sources and costing only a few dollars U.S. To make adjustments, one lowers the pitch of the strings until the strings, with a little effort, can be lifted from their saddle notch and pushed off to one side of the slot, making the string slot accessible for modification (by filing).
It’s a trial and error procedure; the idea is to remove small amounts of nut material then replace the string in the saddle, checking for “buzzes”. Once one approaches an optimum configuration, it takes only a few strokes of the jeweler’s file to remove a significant amount of material, so take care. Repeat the process for each string until all have about the same amount of clearance, string to first fret, and none buzz.
This is a situation where one CAN use feeler gauges with some assurance that the clearance measurement will be meaningful (unlike measuring clearance at the twelfth fret). This is because there is minimal deflection of the string, so close to the nut and it is possible to get a good “feel” when slipping various thickness gauges between string and nut to find the right one.
If you go too far, no matter, start over again with one of the extra nut blanks. The work actually goes fairly quickly but even so, it’s worth spending some time here. (If your string selection doesn’t include wild variations of diameters, you’ll only have to do this work on the nut once. So take some time and get it right.)
When you’re satisfied with the nut configuration, you may want to use a larger, coarser file and reduce the overall height of the nut. In other words, reduce the amount of material that extends above the guitar strings. Many recommendations suggest taking the nut down to about the string center line level. I don’t have strong feelings about that but I feel more comfortable with adjusting the nut height so that it is approximately even with the top of the strings.
At this point, it’s time to establish a baseline configuration. Our work on the nut may have affected the action of the guitar slightly, so we first need to make a preliminary adjustment of the bridge. Because of the different behavior of the large and small diameters of the top and bottom strings, the relief between string and frets will also be different. The first string can always be adjusted to have less clearance than the sixth string, all other things being equal.
The alignment process, whether it is bridge adjustment, truss rod adjustment (or even nut adjustment) requires that the instrument be brought to pitch each time an evaluation of performance is to be made (even if the evaluation is such a simple one as checking for buzzes). And that’s exactly what we need to do at this time …
Bring the guitar to pitch and play every single-note position on the neck, trying to use an attack that you think represents your normal one. Reduce the height of the bridge on each side (first string side and sixth string side) gradually, using the bridge adjustment nuts, until you start to experience “buzzing”. Note that the instrument must be brought to pitch after each bridge adjustment. An inexpensive electronic guitar tuner is invaluable for this and also for intonation work.
Once the bridge has been adjusted to your satisfaction (buzz-free across the normal playing area of the neck), it’s time to make the measurements that establish baseline configuration, even if the current “action” is not acceptable. Using the technique described in detail in Parts 1 and 2, document the fret positions of the first and sixth string as your reference configuration.
If you are VERY lucky, you are satisfied with the guitar in current configuration but it’s never happened to me. I keep tweaking and twiddling because I like low actions. I suspect that frequently I have adjusted my guitar necks back to their original configuration - but at least I know that I have investigated the practical range of adjustment and satisfied myself that no “improvement” is available.
NOW comes the tricky part, the truss rod adjustment, the one that seems to cause the most mischief and misunderstanding.
Remove the small cover on the headstock that covers the truss-rod adjustment nut. I strongly recommend that, before making any adjustments to the guitar, you remove the nut and clean the entire area carefully, using a soft brush, compressed air or both (both available from camera stores at modest cost). Lightly lubricate the threads of the truss rod with petroleum jelly (if you don’t have this, use any light lubricant even cooking oil is OK) before replacing the nut. Screw the nut over the rod until it is snug (finger tight).
Now, measure the distance across the flats of the adjusting nut and confirm that you have a hexagonal socket wrench that exactly fits the nut. Not “almost fits” and not any other kind of wrench (e.g. 12-point), you really need a wrench that not only fits closely but completely confines the length of the adjustment nut for best results.
The socket isn’t costly – about the price of a fast-food meal, so don’t cut corners. The adjustment nuts are universally made from brass and easily damaged. That’s intentional - it is preferable to damage the nut rather than the truss rod !
Using the “optimum” wrench, adjust the truss rod (1/4 turn increments only – smaller is better if you have lubricated the adjustment nut as suggested), making the pick/fret measurements described in Part 1, until the baseline configuration has been restored. Set the guitar aside for at least 12 hours in an environment representative of normal temperature and humidity.
Make the fret/string measurements again and compare with the measurements on the first and sixth strings that were previously made. Don’t be surprised if they differ by a fret or two … The purpose of making the measurements now is to begin the process of “intuiting” the behavior of your guitar and to familiarize you with the measurement process. Oh, by the way, write everything down – keeping good records is a good way to understand what is happening and why, later along when you’ve forgotten details.
Now repeat the bridge adjustment process described above, checking each string for buzzing at every playing position until you are assured that the neck is buzz-free (but just barely if possible). Bring the instrument up to pitch as you make the bridge adjustments and confirm that the final adjustment is made with the guitar tuned.
Measure fret/string configuration again, compare with earlier measurements (again, accumulating intuitive information about how the guitar is responding/moving with your adjustments). Play it for a while, up and down the neck, handling the instrument in a way that is representative of your normal manner. Make a determination as to the performance of the instrument as adjusted, if it’s satisfactory, set it aside, let it “rest” for a day and make one more measurement to make sure that nothing has changed.
If you’re NOT happy with the results now, a decision must be made. (When the guitar is optimum for a particular set of strings, slightly reducing the height of the bridge will cause a buzz throughout normal playing areas – this is the classically desirable adjustment scenario.) You need to consider replacing the strings with ones that have different characteristics and start over again with the optimization process if you feel that the setup “just isn’t right” for you.
Sometimes one finds that just one string is a problem … for example, everything plays great except for the SECOND string, which buzzes when the other strings sound fine. Try replacing the second string with the next larger diameter, it’s not hard to find the right one, provided that you are not using an esoteric set, made from some abnormal material. Just write down what you’ve done so that you’ll remember the next time that you buy strings.
It’s worthwhile to point out that by now most guitars should have reached a point of diminishing returns and you will notice only very slight improvement for very large amounts of time expended. Decisions about further work on the instrument need to take this into account.
If you have a “young” guitar (perhaps from a manufacturer that doesn’t observe careful materials selection and aging) it’s possible that the guitar is still moving around. There’s not much to do about this except to allow time to pass … years may be required, who knows ?
Summarizing the adjustment process:
Adjust the nut
Adjust the bridge
Adjust the truss rod
24 hour stabilization
Iterate as required
After one is satisfied with performance and stability, intonation can be addressed.
Intonation is a misused term that describes the inability of an instrument to produce the tones of a specified scale. In our case, the so-called “even-tempered scale”. (Please run both terms through an internet search to obtain specifics in the unlikely event that you are unfamiliar with them.)
We don’t have very much latitude in the correction of intonation problems. Usually, the only adjustments made during setup/maintenance are those that are harmonically related. The process is simple but – unless one is young (good ears) and possesses accurate pitch – normally requires an electronic tuner. Many years ago, this was a drawback but tuners these days are almost throwaways, in terms of cost.
The adjustment procedure that I’ll describe doesn’t require an instrument of any particular accuracy, since we are only interested in the relative difference between two tones and not their absolute accuracy. This is a well-discussed procedure and should be familiar to all.
(Without diverting TOO much from the main topic, some explanation may be in order. All electronic tuners use a crystal oscillator to establish a reference tone, they employ digital frequency dividers to process the reference frequency into tones to which we want to tune. In simplest form, what this means is that we can’t depend on absolute frequency accuracy but we CAN depend on the fact that the tones are integer multiples or divisors of the reference frequency, so if we want to compare harmonics, ANY tuner – regardless of frequency accuracy – is adequate for the purpose, despite contradictory assertions.)
After tuning the guitar to pitch, the procedure requires striking a harmonic on each string and examining the indication of frequency on the tuner. (Generally, if one places a finger lightly right ON the twelfth fret wire – not centered between frets as we usually finger the instrument – it’s easy to produce a harmonic with reasonable amplitude.)
Moving from string to string, play a harmonic, carefully noting the indication of pitch (actually pitch error) on the tuner. Then fret the twelfth position and play the note, monitoring the tuner and noting any difference between the fingered note and the harmonic. The bridge must be adjusted to reconcile differences between the two notes. For TOM (tune-o-matic, Gibson TM) one uses a small screwdriver to adjust individual string saddles until the difference between harmonic and fretted tone is negligible.
For fixed, wooden bridges, a compromise is required. Generally, one makes an adjustment to the bridge (by moving it forward and back) so that the first string and sixth string harmonics are equal to their fretted notes. If the bridge compensation is carved correctly for the set of strings you are using, and you’re satisfied with the performance then you’re done.
Direction of bridge movement (or saddle movement) is predicated on the pitch error of the fretted note. If it is “sharp”, move the bridge (or saddle) toward the tailpiece of the guitar. For “flat” errors, the bridge (saddle) is moved toward the headstock of the guitar.
If you want to take the correction further (which suggests that your bridge isn’t compensated properly for your particular strings), my suggestion is to play all of the strings and play their harmonics, monitoring the tuner and recording the errors. For convenience, devise a table and chart the magnitude of the errors between tones, noting whether the error is sharp or flat.
Examining the chart can reveal that sloping the bridge at an angle will minimize errors across the entire range. In other words, instead of a perfect high “E” and a perfect low “E” with a “G” that is flat by a magnitude of … say ½ division (on whatever tuner you’re using), you could slope the bridge to obtain high and low “E’s” that are ¼ division sharp and a “G” that is ¼ division flat.
The point is to equalize the errors across the entire scale instead of absorbing the error into one or two strings that will be blatantly obvious. (Having said that, the “blatantly obvious” will probably only be apparent to you – the guitarist – and not to an audience.)
(Do an internet search on the “Buzz Feiten method”, you’ll find mostly discussion of the compensated nut – which is not particularly of interest to me. But if you read the discussion of the entire method carefully, the implication is the same as what I’ve proposed above: that the frequency errors are distributed across the entire scale instead of being concentrated in one or a few strings.)
I haven’t furnished any detail about how the slope of the bridge can be mathematically determined, to equalize pitch errors. That’s because I think that those who are interested in this method will have the capability to easily do it themselves. However, an empirical adjustment, using a tuner and a chart, is within anyone’s capability.
It should follow that, once one has carefully positioned the bridge for intonation, changing strings implies taking a little care to prevent moving the bridge. Most do this by replacing the strings one at a time, depending on remaining string tension to hold the bridge in place. Taping the bridge to the guitar body at both edges is not uncommon.
In summary, once a guitar has been properly adjusted (set up), assuming that the guitar has been carefully manufactured from quality, aged materials and that the strings intended for use will be similar (from set to set), nothing much in the way of maintenance need be anticipated other than ¼ turn or so on the bridge adjustment screws once or twice a year.
25 Oct 09
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