Shim to Fix Buzz on Top Frets?

[LaBottomMe]

Bought a MIJ P-bass about a year ago. (I'm mainly a guitarist, so wanted a bass for recording, etc.) Haven't played it much and never bothered with the setup until now.

- neck looks very straight, so figured truss rod adjustment not necessary (pressing first fret and 16th and string still a bit above 7th fret, so I think neck relief is about right)

- action was still high, so I looked online for suggested height and set it about there (my touch is light, so about 2mm on G at 12th fret; almost 3mm for E string)

So, playing better, overall. But then I noticed playing from about 14th fret and higher there is buzz.

So, I'm wondering if a 'reverse shim' might fix it. 'Reverse,' because it seems shimming is usually done when the neck needs to lay flatter, to allow the bridge to set the action properly without having it in its lowest position. So, instead of putting the shim in the bridge end of the neck pocket, I'd put it in the head end of the pocket. (Then, of course, I'd need to lower the bridge as the shim would make the action higher along the length of the neck.)

I'm thinking that the part of my neck where it attaches to the body is too flat, and needs to tilt up a bit, so there is some string angle between the the bridge and the higher frets. The action is good along most of the neck; it's just the higher frets that have a problem.

Or is something else going on?

 

[Chasarms]

EDIT: I would remove a bit of relief from the neck to see if you can get the desired results.

 

[LaBottomMe]

I would add a bit of relief to the neck to see if you can get the desired results.

I could try that. But I don't understand how that would effect the angle of the strings from fret 14 and higher to the bridge. Since the neck is bolted to the body in that area, I would think truss rod adjustment would mostly effect the curve of the neck from the nut to about the 14th fret.

 

[Chasarms]

I could try that. But I don't understand how that would effect the angle of the strings from fret 14 and higher to the bridge. Since the neck is bolted to the body in that area, I would think truss rod adjustment would mostly effect the curve of the neck from the nut to about the 14th fret.

Sorry, I didn't read your post closely enough. I should have suggested that you try a bit LESS relief.

When the neck bows under tension, the relative position of the nut to the plane of the bass body (and thus the bridge) changes. A bit less relief, or less bow, will lower the nut, making the path of the strings from the nut to the bridge more parallel and allowing lower action.

Just try a quarter turn at a time, re-tuning and adjusting the action until you find the sweet spot. The final result will be dependent upon the neck and the quality of the fret work. Once you get it best results, be sure to reset the intonation. It will be off, and once you do, you may have to tweak the action a bit more.

 

[Lownote38]

I could try that. But I don't understand how that would effect the angle of the strings from fret 14 and higher to the bridge. Since the neck is bolted to the body in that area, I would think truss rod adjustment would mostly effect the curve of the neck from the nut to about the 14th fret.

What you have cannot be corrected with a shim, or a truss rod adjustment (and adding relief would actually make it worse rather than better). It's the dreaded ski jump which is where the neck angles up at the neck joint, but not anywhere else. It's a common issue with Fender Basses, and any bolt on neck bass for that matter. Sometimes, if the issue isn't too bad, the frets from 14 on up could be worked on and re-crowned to a lower height to compensate for the ski jump. If it's really bad, sometimes the frets can be removed, and the fret board re-planed to take out the jump. The frets are then reinstalled and the problem is fixed.

 

[Turnaround]

A couple of corrections to what has been noted so far...

It was noted that the ski jump condition is common to basses with bolt-on necks, suggesting that it has something to do with the neck being bolted on. In fact that has nothing to do with a ski jump condition. Look At the study that was done by a number of luthiers that participate in TalkBass. It's in the Pro Bench sub forum.

A shim is not going to help as Lownote38 has said. However it can be helped somewhat by an adjustment to your relief. Tighten the truss rod a bit to lessen relief, then raise your saddles to compensate for the lowering of the strings that occurred as a result of the truss rod adjustment. You may end up with the action a bit higher than your ideal but it may be worth the compromise. Otherwise you will need the remedies Lownote38 outlined.

 

[Lownote38]

A couple of corrections to what has been noted so far...

It was noted that the ski jump condition is common to basses with bolt-on necks, suggesting that it has something to do with the neck being bolted on. In fact that has nothing to do with a ski jump condition. Look At the study that was done by a number of luthiers that participate in TalkBass. It's in the Pro Bench sub forum.

A shim is not going to help as Lownote38 has said. However it can be helped somewhat by an adjustment to your relief. Tighten the truss rod a bit to lessen relief, then raise your saddles to compensate for the lowering of the strings that occurred as a result of the truss rod adjustment. You may end up with the action a bit higher than your ideal but it may be worth the compromise. Otherwise you will need the remedies Lownote38 outlined.

I've just noticed the condition more on bolt on neck basses, but maybe that's because bolt on neck basses are more common. You're right that it can be helped out somewhat with a neck relief adjustment, but a lot of times you end up with a dip, or a hump in the neck and higher action will be necessary (as you mentioned).

 

[Turnaround]

I've just noticed the condition more on bolt on neck basses, but maybe that's because bolt on neck basses are more common. You're right that it can be helped out somewhat with a neck relief adjustment, but a lot of times you end up with a dip, or a hump in the neck and higher action will be necessary (as you mentioned).

Anything less than a re-planing is a compromise. Lowering the upper frets by dressing often compromises intonation if the ski jump is not trivial since the amount of fret that must be removed doesn't leave enough to crown properly. But it's a decent option for treating a mild ski jump. So is raising the saddles while reducing relief. If a customer is looking for inexpensive options, I start with relief/saddles height before going to fret dressing or fretboard levelling - least intrusive to most, progressively.

 

[LaBottomMe]

A couple of corrections to what has been noted so far...

It was noted that the ski jump condition is common to basses with bolt-on necks, suggesting that it has something to do with the neck being bolted on. In fact that has nothing to do with a ski jump condition. Look At the study that was done by a number of luthiers that participate in TalkBass. It's in the Pro Bench sub forum.

A shim is not going to help as Lownote38 has said. However it can be helped somewhat by an adjustment to your relief. Tighten the truss rod a bit to lessen relief, then raise your saddles to compensate for the lowering of the strings that occurred as a result of the truss rod adjustment. You may end up with the action a bit higher than your ideal but it may be worth the compromise. Otherwise you will need the remedies Lownote38 outlined.

Before I posted this question I did search for "shim" and read parts of some threads, including the beginning of the "ski jump" thread. Great that you guys who have the knowledge, time and interest to look at these matters.

OK, now I have a better understanding...that tightening the truss rod a bit, *combined with raising the saddles*, WOULD change the angle of the strings from the bridge to the upper frets, and is worth trying.

I honestly don't anticipate playing that high on the neck very often (but I'd certainly like to retain the option). I'll try that tomorrow (it's 1:30am in Bangkok). Guessing it will help at least a bit and may do the job. If not, I'll probably live with it, as it's hard to find reliable guitar techs here that aren't booked months in advance. (Prices are reasonable, though.)

 

[Lownote38]

Anything less than a re-planing is a compromise. Lowering the upper frets by dressing often compromises intonation if the ski jump is not trivial since the amount of fret that must be removed doesn't leave enough to crown properly. But it's a decent option for treating a mild ski jump. So is raising the saddles while reducing relief. If a customer is looking for inexpensive options, I start with relief/saddles height before going to fret dressing or fretboard levelling - least intrusive to most, progressively.

I hear ya. I guess I'm super particular with my own basses, and I could never compromise with a ski jump situation. Luckily, my '68 Precision Bass could be fixed (due to this problem) with some fret work on the upper frets. The frets had barely ever been touched and are original, so my favorite repair guy here in Nashville lowered them down a bit and re-crowned them. The ski jump was mild, but seemed huge to me.

 

[LaBottomMe]

So, yesterday I got back to looking at the setup on my MIJ P-bass. Sure enough, by tightening the truss rod a bit, then raising the action, I was able to get it to an acceptable condition. So thanks very much for helping me with that. There is still a bit of buzz around the 18th fret, mainly on the A string, but it's livable...and I doubt I'll play up that high very often. Of course, I then revisited the intonation and dialed it back in.

As I said, I'm mainly a guitarist (over 50 years now), so will primarily use the bass for my home recording ideas. (But might occasionally bring it to a jam or something.) This is the first time I recall ever setting up a bass. Of course, I have set up my guitars many times, but don't often play with the truss rod. (I did work in an Epiphone receiving warehouse many years ago inspecting the ones that came in to Seattle from Asia at that time. Most of that was, unfortunately junk. But we would go as far as re-leveling and re-crowning frets, etc., when warranted.)

I bought the bass in the Chinatown area here in Bangkok, Thailand. The day I tried it, I loved how it sounded through one of the bass amps they had in the store. So, a couple days later I went back and bought it. At first, the kid pulled a new one of the same model out of their storeroom...but after playing both, I said I preferred the original one. Well, what's done is done, but now I wonder if the one I bought--which had been in a stand in their display window, for who knows how long...in the Bangkok heat--was the poorer choice. Nah, it had the mojo for me; and I still like it. And maybe the 'new' one also suffered from skijump-itis?

It was interesting to see how relatively small adjustments on the truss rod effected the neck. Of course, I tightened it a bit too much, then backed it off to find the sweet spot between proper neck relief and dealing with the ski jump at the upper frets. I guess, overall, I only tightened it about an 8th turn. (?)

Though I'd guess many here think it's ridiculous, I kind of like to tune the whole thing down a full step (D G C F), sometimes. So tuned it down to see if it still played OK in that tuning. In the end, I found a setup that works under both tunings.

As I've never been a serious bassist, I'm not really sure how a good bass is supposed to feel. I did play a friend's bass a while back though, and was surprised at how low his action was and how easy it was to play. (I think this was over a year ago--before I got my MIJ P-bass.) Even after this last tweak, my action at the twelfth fret seems close to what was recommended on Fender's website: around 2mm on G string; 2.5mm or so on E string. So, all seems good!