I have a 1988 Masterpiece. It has a compensated nut; I am using an uncompensated bridge and D'addario J61 medium gauge strings. If I tune to pitch perfectly with open strings, the 2nd (B) string is about 10 cents sharp when fretted up to about the 7th fret, Very noticable. I can tune the open B string about 10 cents flat (what I have been doing), and then it is in tune when fretted, but noticably flat when unfretted.
Am I missing something here? Is there a better compromise - maybe tune the string about 5 cents flat and spread out the error? It seems like the compensation is working against me here.
16 Comments |
 | Geoff Stelling says:
3/18/2014 10:44:37 AM
As usual with a tuning problem I must ask what the set up is with the neck's truss rod. Is the second string the only one to play sharp, and are you sure that the second is not sharp all the way up the neck and not to the 7th fret only? It would be helpful to know the string height at the 12th and the 22nd frets and of course the bridge position.
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 | dpskala says:
3/18/2014 11:51:16 AM
OK, I thought I had covered all the bases, but I did forget to document the setup. Yes, it is only the second string which is problematic. If I tune it open to a true B, it is sharp from the 3rd fret to about the 7th fret. Of course it gets better after that, and is pretty much back to a true B, one octave higher, at the 12th fret. I set the bridge by chiming the strings, matching the chime to the fretted 12th. I just measured, and the bridge is 7-1/2" beyond the 22nd fret. String height is 1/8" at the 22nd fret, neck bow is set with the truss rod as recommended in the manual. I just measured height at 12th fret, and as best I can measure, it is 9/64".
The compensation on the 2nd string is much more than any of the others - you can see that in the picture at the left. My nut looks exactly like the picture.
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| Geoff Stelling says:
3/18/2014 12:33:09 PM
As you described your set up, the string height for the 22nd and 12th frets appears to be reversed as it should be for proper neck bow. I recommend 9/64" at the 22nd with 1/8" at the 12th. Yours is exactly the opposite. I also measure my bridge position from the top center of the 12th fret to the top center of the bridge (13 3/16") which should be parallel to the frets. Try making those adjustments and let me know how it goes.
Geoff
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| dpskala says:
3/18/2014 2:28:33 PM
Thanks, Geoff. My bridge position is exactly 13-3/16". I rechecked my neck bow, which I had adjusted as per the picture on page 3 of the field service manual. The clearance at the 7th fret, string to fret, is about 0.024" (feeler gauge). I rechecked string heights using the shanks of drill bits. At 22nd fret, it is 1/8"; at 12th fret, it is just a little less than 1/8", but more than 7/64". However, it just occurred to me - I am measuring those last 2 string heights from the fretboard. I suspect that is wrong, and that you are going to advise me to raise the string action by the height of the frets (1/32"). I can do that, but once I have adjusted the neck bow to spec, the relative string heights at the 12th and 22nd frets should stay about the same. I guess I could reduce the bow a little. But are these tiny tweaks going to have any noticeable effect on the tuning issue?
BTW, nowhere in the field service manual or in your setup system instructions (3/88), is there any mention of bridge height. I am using a 5/8" bridge, uncompensated, standard spacing.
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| Geoff Stelling says:
3/18/2014 2:59:09 PM
The bridge height should not have any effect on the set up since we are considering string height above the frets (not fret board). Neck bow does have a big effect on tuning since the more the strings have to stretch, the sharper they play. Obviously, the most bow would be around the 7th fret, so that's where the most tuning problems would occur. I'd say your tuning issues are with the neck bow being too severe. Other than that, if the compensation was cut too far into the nut, it could cause tuning problems (sharp), but they would be noticeable all the way up the neck. If you have a scale that is small enough to go down into the second string slot, see if the slot is cut to 1 17/32" from the most forward part of the cut in the slot to the trailing edge of the of first fret. In other words, the compensation is that distance from the edge of the first fret's upper most edge (closest to the 2nd fret) to the part of the nut the string starts to vibrate from (trailing edge of the nut at that point). Too much compensation makes it play sharp. Too little makes it play flat. String diameter plays a role, also. Thicker strings play flat and thinner strings tend to play sharp. And in my opinion, the 2nd string on a banjo is the most difficult one to tune.
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| Geoff Stelling says:
3/18/2014 3:02:44 PM
I apologize for the extra word "of" on the end of the 25th line. I hope the rest reads ok.
Geoff
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| dpskala says:
3/18/2014 3:39:06 PM
OK Geoff, measuring the 2nd string compensation as you describe, I get exactly 1-1/2" --- 1/32" under spec. I was going to say I'll back off on the neck bow to the minimum value and bump up the action to your recommended value; but maybe I ought to address the nut issue first. What do you think? If I mailed the nut to you, could you cut it to spec?
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| dpskala says:
3/21/2014 4:30:10 AM
I lowered the neck bow to about 1/64" (that is as low as I can go - the truss rod nut is now all the way clockwise), and I raised the action to about 1/8". That cut the problem in half, to barely perceptible. I can tune the second string about 5 cents flat, and it sounds good all over the neck. If the 2nd string compensation were increased 1/32" to bring it to spec, I imagine it would be perfect.
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| Geoff Stelling says:
3/21/2014 9:57:21 AM
Dennis,
We've posted a lot of words about this subject and I am getting a bit confused. Your original problem was that the second string played sharp by 10 cents. Now, with all the adjustments it plays only half as sharp as before, but you want to increase the compensation by 1/32" ? I'd say the compensation needs to be reduced. But, I have an easier solution. Since redoing a nut should be done with the entire neck in hand, I think compensating the bridge for that particular string would be the cheapest, fastest, and most accurate cure. Compensation works at both ends of the string and it is not unreasonable to do it at both ends if necessary. For a string that plays sharp, you can simply notch the bridge slot back toward the tail piece to flatten it. Conversely, to sharpen a string, you would add to the front edge of the bridge, as in my compensated bridge design. As I said before, adding to the cut out at the second string nut slot would further sharpen the pitch of the played string. If your bridge is wide enough, just take a small amount off of the front edge of it at the second string notch. I guarantee that that will solve your problem. If you need a custom bridge made, I can do that for you. Let me know.
All the best,
Geoff
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| dpskala says:
3/23/2014 6:37:44 PM
Geoff, you're quite right. Now I'm confused too. It does make sense that if anything is amiss with compensation, I have too much now. I'll remeasure the 2nd string slot depth - I had just wedged a thin metal scale beside the taut string and butted it up against the back of the slot in the nut. I'll move the string out of the way and try again.
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| dpskala says:
3/24/2014 9:04:45 AM
OK, I remeasured, and forward slot to trailing edge of first fret is really 1-1/2". The 2nd string slot is 3/16". So compensation is a little below spec. In spite of this, I am still very slightly sharp. I guess I could notch out the other four slots on the bridge by 1/32" and move the bridge up by that amount, but it's not worth the bother at this point. 5 cents off is almost imperceptible (to me anyway), so for all practical purposes, problem solved. Your recommendations re. bow and action did the trick.
I do appreciate your advice.
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| Geoff Stelling says:
3/24/2014 9:15:32 AM
Remember, you still have the option to compensate the bridge as needed to make it perfect. Glad you are better off now than before.
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 | tony wall says:
3/28/2014 11:15:21 AM
Hi i also had this problem wit the b string sharp wen fretted and flat wen tuned openly i tried everything to sort it wat i done was put a heavier gauge string on the b and that sorted the problem mine was a red fox aswell i reckon ur strings are to light try that and i reckon it will work
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| dpskala says:
3/28/2014 1:23:07 PM
Just put a heavier string only on the B -- interesting. Mine are medium strings on a Masterpiece, but the problem is the same. I'm pretty close to imperceptible now, but I may give that a try. Thanks for the insight.
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| dpskala says:
3/28/2014 1:39:29 PM
I just quickly looked online, and I can't find a set of strings with a B string heavier than 0.012". Where can i get such a critter? A medium low G string tuned up seems unreasonable.
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| tony wall says:
3/28/2014 6:58:06 PM
I find that most sets of strings that say10 is really only a 9 and 11 may only b a 10 cant really remember i think my b is a thirteen from a guitar set i tried everything on my red fox had to tune up every time i played it drove me nuts went to a banjo builder first thing he said put on a heavier string it solved the problem in seconds a lot of banjo players dont know this will solve the problem regards tony
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