Bass Precision
Tracking Down a Buzzing A String
On the bench today, we've got a contemporary U.S. made Fender P-Bass. Local Grand Rapids musician, Tim Hamm, contacted me earlier in the week about tracking down a buzz he was noticing on his A string.
Getting the right action, relief, and intonation on a bass is tricky. Bigger strings need a greater distance to travel in their vibrating ellipses above the fingerboard and the 34" scale imbues a greater amount of stress on both the neck wood and truss rod, so I immediately assumed the bass just needed a set up. It was after Tim affirmed that he heard the unpleasant overtones when the string was played unfretted that I began to think the nut might be the one getting it's buzz on.
Check out the following video. You can hear the A buzzing away until I apply some pressure to it behind the nut. It's a pretty simple test you can do yourself if you're trying to track down some unwanted vibrations.
After test playing the bass, I was about 90% certain the trouble was in the nut, but once I slackened the strings and pulled them aside I could actually see what was happening. Tim had switched from D'Addarios to DR Black Diamonds, and lucky for me, the black coating left an imprint, visually demonstrating how each string was making contact in the nut slot. It's a little hard to see in the photo, but the E, D, and G strings all showed a nice solid line in each slot, indicating good contact. The A, however, left 3 distinct points of contact on the sides and bottom of the slot. A tone killer for sure.
Once I saw this, I set about reshaping the slot with my nut files. Since cutting the slot too wide or too deep would necessitate an entirely new nut, I sneaked up on this one by degrees. After a couple of tries, I had it. No more zzzzzzzzzzzz on the open A.
I also noticed that the bass had an excessive amount of neck relief. Check out this picture of the 12th fret area when I set my old 32" level across the frets. Keep in mind that the level is resting on the crown of the first and last frets here. Major back bow. Upper fret access would definitely be uncomfortable at this string height.
A good way to understand neck relief, truss rod adjustment, and playing action is to imagine a fishing rod that's been reeled all the way up so that the hook is caught on the last eyelet. When pulled taught, the line (the strings) creates a bow in the rod (the neck.) The tighter you reel in the line, the more the rod bows and the greater the distance between the line and the rod. On a guitar or bass, this is the neck relief, otherwise described as the action of the neck. Tightening the truss rod helps counteract this tension mechanically, by bowing the rod into the opposite position. Unfortunately, time and tension almost always win in the case of a 34" scale bass, and the rod eventually begins to weaken, leading to a permanent back bow and eventual unplayability.
A technique I learned a few years ago "pre-loads" an up bow (negative relief) into the rod when it isn't under tension. When the strings are tuned back up, the truss rod gets pulled back to straight, and the action can be adjusted much lower. I recommend it for every single bass and apply it to my basses at every string change.
Check out the following video. You can hear the A buzzing away until I apply some pressure to it behind the nut. It's a pretty simple test you can do yourself if you're trying to track down some unwanted vibrations.
After test playing the bass, I was about 90% certain the trouble was in the nut, but once I slackened the strings and pulled them aside I could actually see what was happening. Tim had switched from D'Addarios to DR Black Diamonds, and lucky for me, the black coating left an imprint, visually demonstrating how each string was making contact in the nut slot. It's a little hard to see in the photo, but the E, D, and G strings all showed a nice solid line in each slot, indicating good contact. The A, however, left 3 distinct points of contact on the sides and bottom of the slot. A tone killer for sure.
Once I saw this, I set about reshaping the slot with my nut files. Since cutting the slot too wide or too deep would necessitate an entirely new nut, I sneaked up on this one by degrees. After a couple of tries, I had it. No more zzzzzzzzzzzz on the open A.
I also noticed that the bass had an excessive amount of neck relief. Check out this picture of the 12th fret area when I set my old 32" level across the frets. Keep in mind that the level is resting on the crown of the first and last frets here. Major back bow. Upper fret access would definitely be uncomfortable at this string height.
A good way to understand neck relief, truss rod adjustment, and playing action is to imagine a fishing rod that's been reeled all the way up so that the hook is caught on the last eyelet. When pulled taught, the line (the strings) creates a bow in the rod (the neck.) The tighter you reel in the line, the more the rod bows and the greater the distance between the line and the rod. On a guitar or bass, this is the neck relief, otherwise described as the action of the neck. Tightening the truss rod helps counteract this tension mechanically, by bowing the rod into the opposite position. Unfortunately, time and tension almost always win in the case of a 34" scale bass, and the rod eventually begins to weaken, leading to a permanent back bow and eventual unplayability.
A technique I learned a few years ago "pre-loads" an up bow (negative relief) into the rod when it isn't under tension. When the strings are tuned back up, the truss rod gets pulled back to straight, and the action can be adjusted much lower. I recommend it for every single bass and apply it to my basses at every string change.
This is exactly what Tim's P-Bass needed, and after I was done, the playability was greatly improved!
Here's couple more pics from the repair session:
I did notice something unusual about the treble side fret ends. Check out the pic. It almost looks like there was tear out when the fret slots were cut and the voids were filled with some sort of epoxy. I've never seen anything like this before.
I suppose a lesser company would have just left the gaps, but then again, why was there tear out in the first place? If anyone else has run across this, please let me know.
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