Zeppelin Design Labs VPM-1 User manual

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VPM-1
VOLUME PEDAL MOD FOR THE ERNIE BALL VP JR.
Owner’s Guide
© 2018 ZEPPELIN DESIGN LABS. NO PART OF THIS DOCUMENT MAY BE REPRODUCED WITHOUT WRITTEN PERMISSION FROM THE AUTHOR. ZEPPELIN DESIGN LABS TAKES
NO RESPONSIBILITY FOR ANY DAMAGE OR HARM THAT MAY COME TO ANYONE OR ANYTHING THROUGH THEIR PRODUCTS.
031620
INTRODUCTION ...................................................................................................... 3
ABOUT THE ERNIE BALL VOLUME PEDAL............................................................... 3
HOW THE VPM-1 WORKS................................................................................... 4
AUDIO SPECIFICATIONS........................................................................................... 7
FEATURES ................................................................................................................ 7
9V POWER JACK ................................................................................................ 7
INPUT JACK........................................................................................................ 7
OUTPUT JACK..................................................................................................... 7
GAIN KNOB ...................................................................................................... 8
TAPER BUTTON / LED INDICATOR ........................................................................ 8
TUNER/EXP JACK................................................................................................ 9
MAIN BOARD DIP SWITCH................................................................................ 10
EXPRESSION UPGRADE ..................................................................................... 11
STEREO UPGRADE ............................................................................................ 12
PANNING CONFIGURATION..........................................................................12
TRADITIONAL STEREO CONFIGURATION:........................................................13
REVERSE TREADLE ACTION................................................................................ 13
APPENDIX 1: INSTALLING THE “READY-TO-INSTALL” VPM-1 ........................................ 14
APPENDIX 2: CALIBRATING THE VPM-1 .................................................................... 22
APPENDIX 3: REPLACING THE DIGITAL POTENTIOMETER........................................... 25

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INTRODUCTION
ABOUT THE ERNIE BALL VOLUME PEDAL
The Ernie Ball volume pedal has been around since 1975. The chassis of these early volume pedals was
originally made from two pieces of angle iron welded together, which
earned them a reputation of being extremely robust. Later, the
chassis was replaced with a solid aluminum extrusion that
greatly reduced the weight while retaining the structural
integrity of the original. A somewhat novel approach
was used to alter the value of a volume potentiometer
incorporating a string and a set of springs, reminiscent of
the tuning wheel on older analog radios. Over the years,
some minor mechanical and electrical design changes have been
made, but the general concept of how these pedals work has remained
the same.
The Ernie Ball volume pedal has a lot of great features. Being made out of solid aluminum,
it is nearly indestructible. The string and spring mechanism for turning the potentiometer creates a
very smooth response in volume. Also, the placement of the axle on the treadle makes for a very
comfortable pedal action. It’s no wonder that the Ernie Ball volume pedal is the most popular volume
pedal in the world.
But for all its great features, there are a couple of
serious down-sides to this pedal. Since the audio
signal is sent straight through the potentiometer, any
problems with the potentiometer are directly translated
to the audio signal. This means that if the potentiometer gets
dirty or worn out, the audio signal can sound scratchy. Also,
the passive nature of this pedal means that the electrical load of
the potentiometer can have drastic tonal effects on the signal.
Any stray capacitance in the guitar cable or anywhere else in
the system will create a RC (resistance-capacitance) filter when
coupled with the given value of the potentiometer. When the
potentiometer is turned all the way up, to a higher resistance,
this effect is less noticeable; but when the potentiometer is
turned to a lower resistance, the high frequencies in the audible range start to become attenuated.
This is what causes the “tone suck” effect when adjusting the volume control on a passive guitar. Many
musicians have resorted to adding a buffer pedal before their passive volume pedal to help rectify this
issue.
Another serious issue with these Ernie Ball volume pedals involves the string and spring mechanism
for adjusting the potentiometer. Over time, the string can actually stretch and cause the action of the
pedal to be off. This often manifests itself in the potentiometer not getting turned all the way in one

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direction or the other, which prevents the audio signal from getting as loud or as quiet as it should.
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

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parameters of how the signal is processed. First, we’ve incorporated five different tapers (or sweeps,
or response curves), including logarithmic, linear, and reverse logarithmic. Next, we’ve included a
“reverse” feature that allows you to reverse the treadle action. Finally, one of the most useful features of
this mod is the ability to program the pedal positions for minimum and maximum volume, which allows
you to set the active range of the pedal’s sweep.
The Gain knob adds up to 14 dB gain to your signal. The TUNER jack provides a buffered split signal
which you can route either to a tuner or to a second signal chain.
The VPM-1 comes standard in mono configuration, but stereo configuration is available with a small
add-on upgrade board. In the stereo configuration, the VPM-1 can operate as either a traditional
stereo volume pedal where both audio channels get louder and quieter together, or it can operate
as a “pan” pedal, where one audio channel gets louder as the other gets quieter. Pan mode enables
the user to pan between two different signals. Another add-on upgrade board gives the VPM-1 the
ability to be used as an expression pedal, with programmable settings to accommodate the different
expression jack wiring configurations found on a wide range of effects pedals.
Figure 1: VPM-1 Block Diagram

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Figure 2: VPM-1 Chassis Front
Figure 3: VPM-1 DIP Switch Locations

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AUDIO SPECIFICATIONS
Parameter Value
Maximum Gain 14 dB (@ 1 KHz)
Maximum Input Voltage > 5 Vpp (@ 1 KHz)
Typical Gain Reduction (Volume Off) > -70 dB (@ 1 KHz, Unity Gain)
Current Consumption ~50 mA (9 V DC Input)
Input Impedance 1 MΩ
Output Impedance ~200 MΩ
FEATURES
1. 9V POWER JACK
You can power your VPM-1with a typical 9V DC pedal power supply (“wall wart”). It must be rated for
at least 100mA, with center-negative polarity. To avoid power supply noise and ground loop hum, it
is possible to connect a battery to the VPM-1 by using a “barrel-to-9V-battery-snap” adapter. Just make
sure that the adapter is wired correctly with the positive terminal of the battery connected to the outside
of the barrel jack. The actual current draw of the VPM-1 is around 50mA, so a battery probably won’t
last too long if it is left plugged in, but it is a good way to troubleshoot noise issues.
2. INPUT JACK
The input jack of the VPM-1 accepts a normal 1/4” instrument cable. It can also accept a TRS cable
or stereo cable for stereo use (see “STEREO UPGRADE” on page 10). The input impedance of the
VPM-1 (in either mono or stereo) is 1 mega-ohm.
3. OUTPUT JACK
The VPM-1’s output jack can accept either a mono instrument cable or a stereo TRS cable (see “STEREO
UPGRADE” on page 10). The VPM-1’s output impedance is ~200 mega-ohms, so it should not have
any trouble driving long cable lengths or other heavy loads.

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4. GAIN KNOB
The VPM-1 uses a power boost converter to change the 9V DC power supplied to the circuit into18V,
which allows for a significant amount of clean headroom for the audio signal. Because of this, the
gain knob can add up to 14 dB of gain to the signal. In the fully counter clockwise position, the gain
is at unity (no signal gain added). “Figure 1: VPM-1 Block Diagram” on page 5 shows this knob
controls the gain of the first amplifier stage, right before the voltage dividing optocouplers. We suggest
keeping the gain at 0 unless you need a signal boost, and then only use as much gain as you need to
drive your amplifier or other pedals. 14 dB of gain is a significant increase in signal voltage, and can
easily overdrive the inputs of most other electronic devices. So please use with caution.
5. TAPER BUTTON / LED INDICATOR
The VPM-1 is a “multi-taper” volume pedal. The “taper” of the pedal refers to how quickly the volume
fades in and out at different points along the treadle’s sweep. On a logarithmic taper the volume
comes in very slowly at the start of the treadle’s sweep but gets louder very quickly toward the end
of the sweep. This is illustrated by the purple curve in “Figure 4: VPM-1 Response Curves”. On a
Figure 4: VPM-1 Response Curves

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reverse logarithmic (or inverse logarithmic) taper the volume comes in very quickly at the beginning
of the treadle’s sweep, but then increases slowly toward the end of the sweep. See the aqua curve
for an example. A linear taper has the same volume change per treadle movement all the way
through the sweep, such as the blue curve.
The VPM-1 has five different tapers to choose from: 2 logarithmic tapers, 2 reverse logarithmic tapers,
and a linear taper. Pressing the taper button cycles through all five tapers. The color of the LED
indicates which taper is currently selected. Figure 4 gives a visual reference for all five curves and their
corresponding LED colors. Once you find the taper that you like best, hold the button down for three
seconds to store it as your “preset.” The VMP-1 recalls its stored preset every time it is powered up.
6. TUNER/EXP JACK
The standard VPM-1 (no expression upgrade) uses the TUNER/EXP jack as a tuner output. When the
Expression upgrade is present, it is used instead as the expression control voltage output. See .
The header labeled “TUNER” on the main PCB must be jumped in order for audio signal to be routed
to this jack. This jumper is already in place if you ordered your VPM-1 pre-built. If you ever need to
remove this jumper, the chassis must be taken out of the pedal in order to access it.
The signal going out of the tuner jack is a unity-gain buffered signal taken directly from the input jack;
no other processing has been done to this signal. In this regard, the tuner output can be used as a
signal splitter to drive another effects chain.

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7. MAIN BOARD DIP SWITCH
The main board DIP switch (shown in on page 6“Figure 3: VPM-1 DIP Switch Locations” on page
6) controls several functions. “Figure 6: Main Board DIP Switch Positions” shows how to set this
DIP switch to control the pedal in different ways. To access this DIP switch while the circuit board and
chassis are still in the pedal, you’ll probably need to use a skinny screwdriver or tweezers.
Figure 6: Main Board DIP Switch Positions

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EXPRESSION UPGRADE
If you opted for the expression upgrade board, the VPM-1 can be used as an expression pedal to
control different parameters on other effects pedals. Using the expression function requires the use of
a TRS (tip-ring-sleeve) cable between the TUNER/EXP jack and the expression input jack of the pedal
you want to control. (Some pedals only require a regular TS instrument cable.) This circuit uses a digital
potentiometer (“pot”) to control a voltage between 0 and 5 volts on this jack, depending on the treadle
position. This circuit emulates an analog expression pedal that uses a traditional potentiometer. The
VPM-1 can not control any pedal with an expression control voltage larger than 5 volts.
To turn on Expression:
1. Turn “ON” Switch 4 on the main DIP switch
2. Turn “OFF” Switch 1 on the expression DIP switch
3. Consult the documentation for the pedal you wish to control and determine how its expression jack
is wired. Consult “Figure 5: Expression Board DIP Switch Settings” and find the configuration that
matches your pedal’s needs. Set Switches 2-5 on the expression DIP switch to suit.
The currently-selected taper will influence the expression output. The “reverse” switch can also be used
in expression mode. See “REVERSE TREADLE ACTION” on page 13.
You can toggle between expression and tuner function by turning “ON” Switch 1 on the expression DIP
switch. This will disable expression and route the audio signal to the TUNER/EXP jack.
Figure 5: Expression Board DIP Switch Settings

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A WORD ABOUT DIGITAL POTENTIOMETERS: The expression upgrade comes with two different
digital potentiometer IC’s (integrated circuits). The digital pot that is installed on the board is labeled
MCP41050, which is a 50K ohm pot. The other IC is labeled MCP41010, which is a 10K ohm pot.
We provide the optional 10K pot because some newer pedals will perform better with this value. If you
would like to replace the digital pot on your expression board please see “APPENDIX 3: REPLACING
THE DIGITAL POTENTIOMETER” on page 25. Please fully read and pay close attention to the
information about static discharge so that you don’t damage your ICs!
STEREO UPGRADE
The stereo upgrade board gives the VPM-1 the ability to control a stereo audio signal. This upgrade
board has a second set of optocouplers on it and all the related circuitry to control the second audio
path. Both sets of optocouplers have been hand selected so that the channels will closely match
each other. The “stereo setup” routine (described in the VPM-1 Assembly Manual) uses software to
help match these optocoupler sets even closer. If you ordered your VPM-1 pre-built, this routine was
performed for you at the Lab.
The stereo function is controlled by the main board DIP switch (see “8. MAIN BOARD DIP SWITCH” on
page 10). Set Switches 1 and 5 to the “ON” position to enable stereo. The two TRS adapter cables
are used to “break out” the left and right channels. Plug them into the input and output jacks. The black
female jack on the adapter is the left channel (tip), and the red female jack is the right channel (ring).
While the stereo function is enabled, the VPM-1 can operate in two ways: panning configuration and
traditional stereo configuration. DIP switch 3 toggles between these two modes.
PANNING CONFIGURATION
When Switch 3 is in the “ON” position, the VPM-1 is in panning configuration. This means that
when the treadle is moved across its sweep, the pedal will pan between the left and right channels.
When the treadle is in the heel down position, only one channel will be audible; when the treadle
is in the toe down position, only the other channel will be audible. The reverse switch determines
which channel is active in each position; see “REVERSE TREADLE ACTION” on page 13. In the
middle of the taper’s sweep both channels will be audible (at half full volume when the linear taper
is used). We suggest using only the linear taper for the panning function; otherwise the sweep will
be lopsided, meaning one channel will fade in and out faster than the other.

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TRADITIONAL STEREO CONFIGURATION:
When switch 3 is in the “OFF” position the VPM-1 is in the traditional stereo configuration. In
this configuration the volume of both channels are adjusted in unison and they will both follow the
selected taper.
REVERSE TREADLE ACTION
The “reverse” function is activated when main board DIP Switch 2 is in the “ON” position. See “Figure
6: Main Board DIP Switch Positions” on page 10. This causes the VPM-1 treadle to behave in the
opposite direction. In this setting, the volume is in the maximum position when the treadle’s heel is all
the way down, and in the minimum position when the treadle’s toe is all the way down. The effect is the
same in Mono, Stereo, and Expression modes. In Panning Stereo mode, the reverse mode will swap
the left and right channels.

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APPENDIX 1: INSTALLING THE “READY-TO-INSTALL” VPM-1
WHAT’S IN THE BOX
Table 1: Ready-To-Install VPM-1 Bill Of Materials
ZDL Part # Description Notes Qty
CB-06-10 Ribbon Cable, 4 wire x 10cm 1
FA-93-35 Lock washer, Split Ring 3.5mm 2
FA-12-15 Magnet 1
PC-11-01 VPM-1 Main Board Assembly 1
PC-11-02 Sensor Board Assembly 1
TP-30-21 Tape, Double Sided, 15mm Circle 1
DC-20-21 Calibration Card 1
CB-06-10 FA-93-35 FA-12-15 TP-30-21 PC-11-01
PC-11-02 FA-93-35

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WHAT YOU WILL NEED
1. #2 Philips screw driver
2. Flat head screw driver
3. Flush cutters or small diagonal cutters
4. Super glue; We prefer the “gel” type because it’s easy to control, but any type will work.
5. Isopropyl alcohol and cleaning rag
A WORD OF CAUTION: This kit contains at least two circuit boards (depending on your
upgrades) on which several types of IC (integrated circuits) components are installed. In
general, ICs are quite sensitive to static electricity and can easily be damaged. Humans are
not sensitive to static electricity at these low, yet damaging levels; in fact, most people can’t
even feel a static discharge less than 1000 volts! So it is easy to damage these components
without even knowing it. Before touching any of the PCBs in this kit, and often while working
with them, ground yourself preferably by touching something grounded to the mains like
the metal chassis of a plugged-in amplifier, or a refrigerator. At the very least touch a large
conductive object like a metal desk or filing cabinet. In our lab, we wear conductive, anti-
static bracelets that are connected to the electrical main’s ground.
PREPARING THE ERNIE BALL VP JR
1. JACK MODULE: With your #2 Philips screwdriver, remove the two jack module screws from the
bottom of the VP Jr (1). Now, use your flush cutters to snip off the wires on the potentiometer (or
you could just bend them back and forth until they break off) (2,3). Hang on to the screws; we will
use them to install the VPM-1 main board module.
1 2
3

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2. POTENTIOMETER BLOCK:
a. With a #2 Philips screwdriver, remove the two screws that hold in the potentiometer block (4).
Note these screws are longer than those from the jack module so keep them separate.
b. Now unwind the string from the pulley to get the block out (5).
4 5
c. At this point the strings and spring should be loose in the pedal. You can pull the strings out
though their eyelets and the spring should just fall out (6-8). You can set the strings, spring and
jack module aside because we won’t be using these again (9-11).
6 7
8 9
10 11

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3. Unscrew the rubber foot from on top of the potentiometer block (12). Once the foot is off, remove
the screw from the foot because we’ll use it later to attach the sensor board (13).
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INSTALLING THE VPM-1
1. RIBBON CABLE: On the long skinny sensor board there is a 4-pin header. Place the ribbon cable
on the header (14). Do you see the little white dot on the PCB, at one end of the header? Let’s call
that Pin 1. Now notice that all four wires of the ribbon cable are marked with unique patterns of
dashes and dots. Note which pattern is associated with Pin 1. You will need this knowledge later.
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2. POTENTIOMETER BLOCK
a. Bend the ribbon cable on the sensor board upward, so it will not conflict with the pulley (16).
Place the two lock washers (part FA-93-35) on the rubber foot screw (17).
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b. Use the screw to fasten the sensor board to the potentiometer block (18). Make sure the PCB
is laying perfectly flat against the top of the potentiometer block (19). Sometimes when the
screw is over-tightened the back of the PCB has a tendency to lift off the block a bit, so make
sure that doesn’t happen.
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c. Align the sensor board with the top of the potentiometer block as in the picture and add a drop
of super glue to the back, top edge of the block (20). This should affix the sensor board to the
block to keep it from rotating as the pedal gets knocked around. It may be necessary to hold
the board down to the top of the block as the glue sets to ensure the board is laying on the
surface of the block (21). Once the glue cures you can tighten up the screw a bit, if needed.
20 21
d. With the sensor board screwed and glued in place, you can now re-install the potentiometer
block in the pedal chassis using the two longer screws (22). There is some play in how this
block fits inside the pedal. Drive the screws snug but not tight. Visually line up the sensor board
so it is aiming straight to the back of the pedal (23), then tighten the screws.
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3. MAGNET: The magnet will be held on the underneath side of the treadle with the double-sided
adhesive disc (TP-30-21).
a. The magnet has a black marking on one side (25). This marking indicates the side that the
adhesive disc should be stuck to. Line the disc up to the magnet and press it firmly into place.
25 26
b. Now we need to attach the magnet to the bottom of the treadle. With your rag and isopropyl
alcohol, clean the area on the treadle directly above the Hall effect sensor (27).
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c. Attach the magnet to the end of a flat screwdriver with the adhesive disc facing up. Then peel
off the backing paper on the adhesive disc (28,29).
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d. With the treadle wide open, place the end of the screwdriver (with the magnet still attached)
on top of the circular part of the sensor board. The circular part of the board serves as a
template for placement of the magnet. Make sure the Hall effect sensor is lined up to the center
of the magnet. The magnet may need to be hanging off of the end of the screwdriver to be
lined up properly (30). When the magnet is in the correct position, bring the treadle down on
top of the magnet and screwdriver. The magnet should stick to the bottom of the treadle in the
proper location (31,32). Press the magnet tightly to the treadle and hold it for a few seconds to
bond it tightly. Now as the treadle moves down and up, the magnet gets closer to and farther
from the sensor.
30 31
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