MIJ Fender Precision Bass Gets a New Nut and Setup

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

Rickenbacker Rick-O-Sound Bass Repair

Craig is a Ric Man.  This beautiful blue bass in only one of his many Rics.  This one has problems with getting both pickups to work.  Could the Unbrokenstring Crew get all this sorted out?

This instrument plays beautifully and has no real discernable setup issues.  However, the wiring seems to be amiss!


More than a few of you will have heart palpitations seeing this head stock.


Two output jacks allow a mono mix of both pickups as is usually found with most multi-pickup instruments, plus a special “Ric-O-Sound” jack that presents the signals from two pickups as two separated signals, accessible with a stereo cable (TRS.)  This gives the player the ability to run two preamps, two effect loops, two separate amps, etc.


Immediately after looking under the pick guard, we find a loose wire.  Poor soldering here.


This isn’t even tinned.


Here is another broken wire, another ground wire.


We have a stack of three inside-tooth lock-washers under each output connector.  Not much spring action available from the teeth of these locking washers, so they don’t really lock.


A magnet is the quickest way to clear all this extra hardware out of the control route.


This is the stereo jack handling the “Ric-O-Sound” duties.


The mono jack handles the single-ended output from this instrument.


Soldering workmanship on the switch needs some attention as well.


Disconnecting each pickup allows us to do some cleanup in the wiring cavity.  The neck pickup is ohmed-out.  The neck pickup is sometimes called the ‘treble’ pickup.


And we do the same with the bridge pickup.  This pickup is also called the ‘bass’ pickup, which seems redundant.


Perhaps this soldering was done with plumber’s solder.  It is awfully dull.


Another look at the switch.  Not much to brag about here.


The ground connection to the control is redone.  Smooth and shiny is the name of the game when soldering.


I labelled the controls BV (Bass Volume,) TV (Treble Volume,) BT (Bass Tone,) and TT (Treble Tone.)


Now that the controls are identified, we can install the knobs in the Correct location.  Yes, they were in the wrong place.


Earlier I pointed out the stack of three inside-tooth lock washers.  Here’s why I mentioned it:


When stacked, the teeth have nothing to push against.  The teeth are literally hanging out in space.


A flat washer in the middle will provide some ‘resistance’ for all the teeth to press against, thus restoring the action of the lock washers to that of being, er, well, lock washers.


The jacks are Imperial measurement and this washer must have been metric.  A little gun-smithing is in order.


The output jacks are wired and tightened into their correct locations.


Testing shows no output.  It has something to do with this volume pot.  What the hey??


This is the hey.  This bit of conductive solder debris was underneath the volume pot, shorting the ‘stapled’ contacts seen in the previous picture to each other, and thus, shorting the output to ground.


Together again, and it’s playing in stereo!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE

JR Beck Six String Bass Blend Pot Adventure

Billy said that he really liked this bass, but the blend pot was coming loose and something electrical was intermittent inside the instrument. Could The Unbrokenstring Crew look it over and make it stage-worthy again?

In literary circles, the term “vanity publishing” is often applied to authors who self-publish their own works. The JR Beck line is a ‘vanity-built’ line of musical instruments, wherein an individual approaches an instrument manufacturer to build instruments under a new name. This bass likely came into the world as part of a contract with a Korean manufacturer.


The neck is straight and the frets are level.  This is a player’s six string bass.


The head stock shape reminds me of an Ibanez profile.


The Grover tuners are really nice.


Someone has been here before.  This screw is too long for the hole.


Just how deep does the hole need to be?  It needs to be THIS long.


We will bore this hole down to the tape go get the length we want.


I can find no markings on the preamp electronics.  The rest of the wiring is a mess around the blend pot.


The duct tape did NOT come from Korea.  Why not get someone who can do this sort of work cleanly, like me?


The blend pot is a hack job.  The rest of the wiring is probably as it was from the factory.


Use more solder if you don’t solder it right the first time.  The solder has actually flowed inside the unit and mechanically interferes with the rotation of the wiper in one of the sections of the control.


We’ve removed the wires from the blend pot.  The cables with the green and yellow jacket come from the pickups. The cable with the white jacket wire goes to the active electronics.


Some RTV was used in an attempt to stabilize the front face of the blend control and keep it from moving when the knob was twisted.  What a mess.


As the control moved around, it scored up the wood body of the bass.  No pick guard on this unit.


To stabilize the wood and prep to mount a new control in a stable manner, a Forstner bit is employed to create a flat-bottomed ‘spot face’ in the wood cavity.  There is some risk of penetration, so we’re going slowly at this point.


A flat-bottom hole is bored without incident.  A steel washer will be epoxied into the body to fully-support the new blend pot.


The new blend pot comes with a couple of flat washers.  I’ll use a lock washer and another nut to set the height of the control so that the knobs are all installed at the same height on the face of the guitar.


A blend pot is a pair of “M” taper potentiometers, which allow one pickup to be faded out as the other side gets louder.  As the control reaches each limit of its travel, the other pickup is electrically ‘cut out’ of the circuit.  In a way, it acts as a selector switch at each end of the travel, with a continuous blend of the two signals in between.


The cross wiring is done with solid 20AWG copper covered with Teflon tubing.  The pickups are wired on the end.


This control has an index pin.  We will cut a slot in the steel washer to ‘catch’ this index pin and hold everything in place.


Initial tests showed that the signals from both pickups were literally ‘grounded’ when the control was set to either limit.  We need to install range-limiting resistors to each end of the controls so that the selected pickup is not grounded at the end of the potentiometer travel.  This is a blend pot, not a kill switch, after all.


It is an easy task to break the connection to ground and install a fixed resistor.  The proper value depends, in part, on the internal DC resistance of each pickup.  It will be easier to discover the proper value empirically.


The box with all the switches is sometimes called a ‘design box.’  The proper name is a ‘resistance substitution box.’  Various values of resistors are switched into the circuit until the desired result is obtained.  Here, we are choosing a resistor value for one side of the blend pot.  Too low a value attenuates the signal.  Too high a value causes hum.


Here is the fixed resistor for this side of the blend pot.  Note the use of the Teflon tubing to keep the signals under control.


Here is the new control installed in its new home.  I am satisfied with the electrical results of this experiment.


The original knob works nicely with the new control.  Note that the knobs are all the same height off the body of the bass.  Another thing I like about this bass is, look at that massive bridge saddle and end block!  The Koreans really know how to do it right.


Jacob takes the finished bass for a spin.  He wants one!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE