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Eventually the string will wear completely out and break. Most long-term Ernie Ball volume pedal users
have experienced this, and usually at the most inopportune times. Few things make a guitarist more
frustrated than not being able to turn up their volume before a solo.
These limitations of the stock Ernie Ball volume pedal have driven a lot of frustrated guitarists to create
their own mods for this pedal. Mostly these mods just incorporate a buffer or boost circuit into the
pedal to counteract the “tone suck” effects of the passive potentiometer. Here at Zeppelin Design Labs,
we have been fans of the Ernie Ball VP Jr for years, and have developed our own mod. Born out of
a frustration with its limitations and a passion for its potential, we have created what we think is the
“mother of all volume pedal mods.” We’ve improved upon every limitation of the Ernie Ball VP Jr while
retaining all the great characteristics that make it the most popular volume pedal of all time.
HOW THE VPM-1 WORKS
Our first goal with this mod was to eliminate the string. We replaced it with a magnetic distance sensor,
called a Hall effect sensor. A magnet is affixed to the underside of the treadle and the Hall effect sensor
outputs a voltage proportional to the distance to the magnet. See Figure 1, page 5. This voltage is fed
into the ADC (analog to digital converter) of a microcontroller. A microcontroller is a tiny computer
capable of receiving and sending voltages. This microcontroller manipulates the brightness of the LEDs
inside a pair of optocouplers, based on the voltage from the Hall effect sensor. These optocouplers
each contain a light-dependent resistor (LDR) which work together to control the volume of the audio
signal. The audio path is completely analog, but it is digitally controlled through the LEDs in the
optocouplers. Because the audio is digitally controlled, we can easily change many parameters of how
the signal is processed. First, we’ve incorporated five different tapers (or sweeps, or response curves),
