I recently bought a used Rickard Dobson (made from one of his kits back in 2011). It's a beautiful instrument, well made and very dynamic. I have some questions about the bridge though. It seems that the instrument came stock with a straight 11/16" bridge. The action and intonation is low and comfortable in the 1st-7th frets but beyond the 7th fret, things get a little wonky.
The notes don't ring as clearly, intonation becomes less accurate, and the notes are harder to fret further up the neck. The tension around the head is even (adjusted with a torque wrench set at 6 inch pounds). Neck relief seems good, but I'm measuring by eye, so there could be something I'm missing. I put an 11/16" medium moon bridge from Elderly which helped the intonation and in general really livened up the tone. To my ear, it is a huge improvement over the straight bridge, but that is another discussion.
I'm still a little curious as to why the 11/16" was chosen to begin with. And I want to know if there is a way to maintain the comfortable action on the first 7 frets and lower the action/improve intonation on the upper frets without doing anything drastic like reshaping the heel, neck reset etc. I tried putting a 5/8" bridge on, and it barely lifted the strings off the fretboard in the first position, so lowering the bridge isn't an option as far as I can tell. I know that adjusting the truss rod is not a solution for action issues, but would tightening the rod help the relief on the upper frets? Thanks for reading! I appreciate any replies. If it helps, the instrument in question is 25.5" scale, walnut neck, 11" thin rim pot with a dobson style tone ring.
Start with a straight edge on fret board, that will show more than your eye.
If you can find a small ruler or straight edge just long enough to cover 3 frets you can do a rock test to see if you have a high fret which wont help the situation. If you can do that up to the 7th fret where you think your problem seems to be at the moment. Look at neck fitment and no gaps at heel. I never suggest tightening coordinator rods to fix a problem.
Sounds like neck bow but lets see if you identify anything.
It sounds like you have a lot of relief.
If you capo at the first fret and hold down a string at a fret where the neck shaft meets the heel, that string is a straight edge (of sorts) and you can measure the relief at its mid-point. You want something like the thickness of a sheet of paper there for the high strings, a little more for the low strings, so you have to find a compromise setting.
Once the neck is the correct straightness, this might lower the action at the 12th, or wherever you measure it, so this then needs adjusting too.
Imagine a neck with an exaggerated bow between the nut and, say, the 20th fret. That neck will be straight after the 20th, creating a kind of hump. Then imagine pressing down the string on each fret, starting at 1. You can see that the height of the string over the hump gets lower as you go up the neck, and at some point will reach the hump and choke out the string. I'm guessing this is what is happening to you, though more subtly of course.
Thank you both for the replies! I was checking relief today and noticed some lifted fret edges, but I don't have any buzz and I don't think that's contributing to the issue I'm having. I think in part, I'm just used to 5/8" bridges and a little bit less relief on the neck. Like I said, it plays beautifully and frets easily up till about the 7th fret. It still sounds good up around the 10th-15th fret it's just much harder to fret the notes than I'm used to. I didn't mention in my first post that the neck has a traditional wooden dowel stick, so no coordinator rods and the truss rod nut is at the base of the heel, so the neck would need to be removed to make any adjustments to relief
You could always try a wedge if you loosen the neck. Something like a credit card strip or thinner between the pot and at the top of the neck. That will tell you if your problem is neck fitment angle. Also try to measure the top circumference of rim and bottom of rim in several spots. If your numbers are different that indicates another issue have seen oval rims that cause neck angle issues.
You have a very nice banjo but you don't know what life it has had and how it was stored
Sounds like some combination of heel angle and uneven frets. Hard to tell without seeing it.
BTW, I'm one of the few people who would know where Ottsville is—I lived near Kintnersville for 10 years and used to run around Nockamixon lake.
I would take it to Bucks County Folk Music shop down in New Britain, not far from you and get them to look at it.
Thanks for the reply Ken! I've been following your work and your posts here for a while so it's nice to get your opinion. I think you're probably right about the uneven frets. I mentioned in a previous post that I noticed some of the fret edges were lifted. Initially I didn't think that was the issue but I had the banjo apart last night and I tightened the truss rod an 8th of a turn. Results were not great. The overall tone fell a little flat, action definitely got lower on the upper fretboard but it didn't make the notes any easier to fret, so the fret edges are probably having more of an effect than I realized. Makes sense. Trying to press the string into an unseated fret sounds like a recipe for decreased playability/tone.
Small world! Lake Nockamixon is my best spot around here for foraging wild mushrooms. This is a great little part of Pennsylvania. Gotta love the Delaware river.
Good idea about bucks county folk music shop! I get my strings and odds and ends from them but haven't gotten any repairs done by them.
Possibly back bow. (opposite of relief) The resulting buzzing at the lower and middle frets would explain why an exceptionally tall bridge was installed, but raising the bridge only results in other problems--like high action elsewhere. Sight down the neck from the nut end and see if the center of the fretboard is high and the ends are low.
Bob Smakula on this forum has had luck straightening warped necks with heat and pressure. If the neck is curved, you could send him the neck and let him diagnose and fix the problem. (Banjos are expensive to ship, but necks are fairly cheap)
If the neck is straight, then the problem may well be the heel cut. Which is fortunately easy to shim if you don't want to re-cut the heel.
Great advice but don't over look the rim. I made that mistake one and found that the issue the second time it came back.
More than likely not your issue but unseated frets will contribute to neck flex also.
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