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.
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.
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.
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.
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.
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.
Thanks for reading all the way to the end!
CONTACT – David Latchaw EE