Intonation Issues on ABG
 

I've been having issues with my ABG, and I finally decided to buckle down and fix it. My ABG has intonation troubles, with every string sharp almost constantly. Short of replacing the bridge saddle, how can I fix this?

What's the make/model ABG we're talking about?
If every string is sharp constantly... is it in tune to begin with?

Yes, I tuned the instrument correctly. The higher the fret position, the sharper it gets in relation to the target tone (comparing octave harmonic to 12th fret, etcetera). It is a Dean EABC (I wanted an ABG, but lacked the ready funds for anything nicer, and still lack the funds to upgrade, so I'd very much like to make this one usable before I purchase a new one).

The neck relief can affect intonation. Try measuring that. The quick and easy way is to use both hands, and hold down the first and last frets of the low E string simultaneously. Have someone insert two playing cards (or business cards) under the 7th fret. If they fit in too loosly, you've got a forward bow (which I think makes the intonation go sharp, but I could have that backwards), and if they fit too tight, you've got a backbow. Either condition can be fixed with a truss rod adjustment, but I recommend you check back in here first (or take it to a pro) before you try to do that.

Have you ever had this instrument setup?

This is not an instrument that I'd put much time & money into.

I don't recall. I haven't touched it in at least a year.

Hi.

Is the saddle/bridge at least in the ballpark of the correct location?

In my limited knowledge about the Deans, that's quite a problem with 'em.

A simple measurement with a tape measure will reveal that.

Regards
Sam

If this instrument is properly set up, and the bridge has been glued in the correct position, putting in a new saddle will impact the tone but probably have little affect on improving the intonation.

If everything is in correct, there are two remedies. If close, a compensated saddle might get it close or right on. If far away, the only alternative is to move the saddle. That means removing the pickup, filling the slot permanently with matching wood, cutting a new slot in the right location, reinstalling the pickup, and trimming or making a new saddle.

Both are a lot of work. Both are expensive.

More than likely the problem resides somewhere else.

Have you set witness points on the strings? This is the thing to do when diagnosing this problem. If the witness points are good, the second place to look is at the nut. Is it tilted one direction or another? Is the speaking face perpendicular to the fingerboard?

If that is o.k. check the string slots to insure that the string is stopped at the bridge end of the nut. It is tricky to see. Rub a pencil in the slot. Detune and retune the string a few times. Loosen the string and look at the bottom of the slot. This will show where the string is speaking. If it is not where it is supposed to be, recut the bottom of the slot.

The B-string rests at eactly 34 inches, T-Bird.

What do you mean witness points?

Hi.

So, it seems the bridge is not far enough back.

A rule of thumb is the scale length + string diameter.


Witness points define the speaking lenght of the string.

If the witness points aren't accurate, the nut slot binds or is cut at an angle towards the FB and/or the sharp(ish) bend at the bridge isn't sharp enough, the speaking lenght isn't what it is supposed to be. As a result, the intonation is off.

The witness point at the bridge is usually set by pressing the string lightly just above the saddle.

Regards
Sam

I believe the witness points are the points where the string passes over the bridge saddle or the nut.

By pressing down on both sides of those points, you create a sharper bend in the string, as opposed to letting it arch gradually over the bridge saddle or nut. The sharper bends create a more accurate break or witness point at the bridge saddle or nut, which makes the intonation more accurate. An angled break is more accurate than a gradual bend.

Just general questions for those with more experience, not necessarily a remedy...
Is there any chance lighter gauge strings would help? or stringing the bass E-C instead of B-E?
How about recrowning the frets to a more narrow profile (after levelling?)
It just seems like extensive bridge work will either be expensive, or will come out looking bad if done by an amateur, which would totally obliterate what little value the bass has. Of course, if appearances don't matter, Or if the bass has a lot of wear already...

Hi.

It will, to a degree.

But if OP's measurement of equal distance from nut to 12th & from 12th to the B saddle witness point is accurate, only piccolo strings will make a real improvement.

No, unless the crowns are moved proportionally towards the nut, ie. the scale is shortened. There's normally not much room for that though, so the improvement is slight at best. Disaster at worst.

I would de-fret it.

Regards
Sam

Assuming the frets to already be in the right place, recrowning is only useful if there is a lot of wear. At which point recrowning should not be performed until the frets are leveled. So recrown is not called for.

Changing to a lighter string gauge may help a bit. But probably not enough to make a difference.

Ultimately, the narrow saddle fixed bridge on an ABG-or any acoustic guitar for that matter, is a compromised intonation. Unless there is a wide saddle ala Ovation that is set to compensate for diameter, there is little to be done other than as indicated as above.

Re: Moving the crowns toward the bridge or nut.

The degree of precision needed to maintain intonation at each individual fret is beyond most techs. Probably all techs. Could it be done with a Plek? Moving the saddle to the right spot, or enlarging the slot for a compensated saddle, would be cheaper.

exactly how did you measure to get that number?

it should be from the fretboard edge of the nut to where the string first contacts the saddle.

to get the actual fret scale length, measure from that leading edge of the nut to the center of the 12th fret; double that is the nominal scale length. that length plus the string thickness is indeed a good ballpark rule for where the saddle should be; as such, even the G should be slightly longer than the nominal length.

if it really is right at 34" on the B, and the scale length really is exactly 34", then you've got a lemon on your hands.

time to get rid of it and look for something else.