tip terminal to the now-vacant overdrive neck PCB hole.
The 1/8” TRS jack is mounted on a small board to the
right of the highest key and is labeled “kick PCB.” I ran
three wires from this board up to the neck area: tip, ring,
and sleeve (Figure 4). The ring and sleeve wires are used
for the next part of our modification.
The 1/8” TRS jack is wired a little differently than you
might expect. The tip is the sustain signal input. It is held
high and looking for a digital 0 (ground) to signal the
keyboard’s electronics. The sleeve is the AD input for the
volume/foot controller potentiometer pedal. The ring is
The tip is looking for an open circuit to ground
connection (switch closure) to send a sustain pedal on
command. A ground to open circuit (switch release)
signals a sustain pedal off command. The sleeve AD input
is looking for a resistance in the 100 to 10K ohm range.
The keyboard’s software also complicates things.
If you go to a resistance below about 100 ohms, the
software tells the keyboard there is no potentiometer
pedal and the volume defaults to full. In this scenario, you
could be decreasing the volume and then when you are
just about at zero volume, the thing will call for full
volume. I suppose this could be used for dynamic effect,
but I just found it annoying.
Also, if the resistance is too high, the software tells the
keyboard nothing’s plugged in and the functions are
disabled. Figure 5 shows the overall electronics block
diagram with the modifications.
Let’s Add Another
The ideal potentiometer to replace the volume pedal
for me is a 50 mm long ( 2”) 10K ohm softpot. Softpots
are made by Spectra Symbol and are available at various
electronic distributors such as SparkFun, Digi-Key, Adafruit,
and Mouser Electronics. Mine cost about $5. You can get
longer lengths, but 50 mm seemed the right length for the
32 January 2016
■ FIGURE 4. "Kick Pedal" PCB. Run three wires from
the tip, ring, and sleeve terminals to the neck area of
the keyboard. The ring is the ground connection and
will need to route to the minimum value side of the
softpot. The left red wire is the sleeve terminal and
connects to the softpot maximum value side of the
softpot. The middle black wire is the ring terminal,
and the right red wire is the tip terminal which
routes to the neck PCB for the new sustain switch.
■ FIGURE 5. Overall block diagram of the Rock
Band 3 keyboard with modifications.
Rock Band 3 MIDI Guide:
Sources for Softpot:
Sources for further information on the Rock Band 3 keyboard, other
modifications, adding sound capabilities, using with softsynths, etc.:
Sites for other DIY Electronic Music Ideas: