Lisa’s marvelous Fender P-Bass needed attention. Some of the open notes were dead, and the electronics needed some attention. Could the Unbrokenstring Crew sort it all out?
I just love the pale yellow finish. Except for a string, everything is here.
Yes, it really is Made In Japan. Back in the day, ‘made in Japan’ was another word for cheap imported junk. Nowadays, this is some of the better stuff, particularly in guitars.
Name, rank, and serial number, please!
An electrical test shows that we have no output.
A quick look under the hood does not reveal an immediate problem. Hmmm…
Oh, this is it. The ground point for the whole unit is this potentiometer body. However, the ground wire to the output lead does not connect to the potentiometer body anywhere.
With that fixed, the remaining ground wires are cleaned up a bit.
The bridge ground wire made an intermittent connection to the bridge. We need to remove the green corrosion.
OK, the electronics are now all up to snuff, and actually look pretty nice.
While we’re here, we’ll tighten the output jack and potentiometers a bit.
The knobs go on now.
Final test is performed with a signal generator and another bass pickup. The signal generator excites the windings in a bass pickup from an Aria Pro II bass, which will be featured in a future blog post. The test pickup is brought near the instrument’s pickups, and the magnetic field carrying a test tone is coupled into the instrument’s electronics.
The dead open notes are traced to a cracked nut. Here, we’re cutting the finish around the old nut so that it can be removed cleanly. The Exacto knife gets a new blade for this operation.
The old nut comes out in two pieces. The crack expanded until the nut broke in two. That’s why we’re replacing it.
Here is the new nut that the customer wanted installed. Good stuff!
Oops. Houston, we have a problem This new nut does not fit the neck.
The new nut is just a tiny bit smaller than what is required for this neck. What gives?
We can clearly see the difference in the sizes between the old nut and the new one. This neck is the width of a five string bass, but it was delivered as a four string bass from the factory. So, we will make a custom nut for this instrument.
A Tusq blank is radiused to match the radius of the fretboard. I’m using an Exacto knife as a scraper.
The Tusq blank is cut to rough length with a fine saw.
It doesn’t take long to slice through the Tusq material with this blade.
This is a saw blade set that I use for sawing fret slots and general fine work on wood.
The blank is now shaped on the disk sander. A piece of birch plywood serves as a raised table that can be placed very close to the abrasive surface of the disk, necessary when shaping small parts.
The blank is now pretty close to the rough shape we need.
The first trial fit shows that we haven’t cut it too small, yet.
This is a little better. The ends are flush and smooth with the edges of the fret board.
In AutoCAD, a drawing is created showing the cross sections of the four strings and the width of the fret board in actual size. The distance between the edge of the outside strings and the edge of fret board, established by factory specs, is drawn, and the position of the outside strings fixed. We then subtract the diameters of the four strings from the width remaining. This result represents the space between strings, which shall be three equal spaces. This establishes the center lines of the inner strings. The spaces between the strings are the same, not the center-to-center distance.
But, to cut the string slots, we need to know where the edge of the fret board is, and where the center lines of the strings fall. These solid lines represent that information.
The lines which represent the centers of each string are transferred to the nut.
A shallow file cut is made at each string center. Here, we are checking these cuts against the template.
These shallow cuts represent the eventual center of each string.
These cuts were made with a triangular mill file. Nothing special, but accurate enough.
Here, we’re polishing up the sides and faces of the nut, in preparation for gluing the new nut in place on the neck.
The nut depth is established by the fret height plus a constant which is established by Fender (and can be adjusted a bit by a good luthier, like me, for best play-ability.) This is the Secret Sauce of making an instrument a great instrument.
The slot depth is now established by this stack of feeler gauge shims. They are held in place with rubber bands wrapped around the back of the neck. I’ve taped off the head stock so that I don’t scratch it up with the end of a file.
When the file touches the stack of feeler gauges, continuity will be detected by this multimeter, and it will beep. This is another check of slot depth, besides my eyeballs.
Here, the slots are cut. With a little cleanup and polish, this will be a good nut!
The nut is all done and polished. Looks good!
The action on this instrument at the twelfth fret is pretty high…
We have a metal neck shim between the neck and body, made from a piece of the machinist’s feeler gauge of the proper thickness to reestablish proper neck geometry. The metal shim is the hardest practical material for this purpose, with an accurate thickness, and better mechanical stability and hardness for greatest vibration transfer between the neck and body than a guitar pick or a piece of business card. This results in the best tone. And a set of feeler gauges are less than five bucks.
A quick adjustment gives us just the right amount of neck relief. (Sharp-eyed readers will spot the fact that the strings are off in this picture. This is the only pic I took of the truss rod adjustment, setting the neck flat while the neck shim was being sized. Who cares if my pics are out of chronological order?)
To set intonation, we needed to work on the bridge. Here is the underside of the bridge, probably not seen for decades.
The intonation screws were dinged. Here, we are chasing the threads with a die to clean them up. Yes, they are English/Imperial threads, not metric.
The bridge is tightened down and ready to go!
The moment we’ve all been waiting for! Add strings, tune up, intonate, and play!
Thanks for reading all the way to the end!
CONTACT – David Latchaw EE
281-636-8626
