To do this you’ll want to use triple-pole double-throw
footswitches (3PDT) instead of the double-pole double-throw
footswitches specified in the original article. The third pole of
each footswitch will be used to switch on an LED when that
particular loop is activated. Any time you are using an LED, a
resistor must be added in series to limit the current from the
battery to prevent the LED from burning up. In this case we’ll
use a 1k½ w-watt resistor, which is small enough to make the
LED burn brightly, but will limit the current to protect the LED
and make the battery last much longer.
To switch the battery off and on, use a Switchcraft stereo
1/4" phone jack (also called a tip-ring-sleeve or TRS jack) for
the input instead of the mono jack as originally specified. Hook
up the tip and sleeve terminals on the jack exactly as indicated
in the original article. The difference is you will connect the
minus lead (black wire) from the battery snap connector to the
ring of the stereo jack. This way, when a 1/4" mono plug is
inserted into the jack, the ring will short to the sleeve (remember
the sleeve is grounded) and the battery will be switched
into the circuit. Always unplug the 1/4" male plug from the
input jack when you are not using the unit as this will conserve
battery power by disconnecting the minus lead of the battery
from the circuit.
You will need some additional parts for this project, and
except for the 3PDT footswitches, all the other parts can be
found at Radio Shack.
PARTS LIST
1 – 9-volt battery snap connector. (Radio Shack part # 270-325)
1 – Battery holder (Radio Shack part # 270-326)
1 – 9-volt alkaline battery
1 – Stereo 1/4" female jack (Radio Shack part # 274-312)
3 – LEDs. Use three different colors. (Radio Shack part #
276-1622)
3 – 1k½ w-watt resistors (Radio Shack part # 271-1118)
3 – 3PDT footswitches (part # P-H501 at tubesandmore.com)
Let’s start building. Look at the diagram (left). The resistors
can be mounted with one lead on the switch and the other
leads flying. You may want to put insulation around each resistor’s
leads to keep them from shorting against other components.
Sometimes I use the insulation from hookup wire to insulate the
resistor leads, but shrink tubing will also work. If you don’t have
shrink tubing, a soda straw could be cut into short lengths and
slipped over the each resistor. It is important to get the polarity
of the LEDs correct or they will not light. You want to ground
the cathode end of the LED. How do you know which is the cathode
end? Look at the leads coming out of the LED. One lead is
shorter than the other. The shorter one is the cathode and must
be grounded. The longer lead goes to the switch.
As with any project, you should spend time planning and
reviewing how all the parts will fit together before you start
building. Take your time and make sure about parts placement
before any holes are drilled. I would suggest installing the jacks
first, then you can see where the switches and other components
should go. The battery holder can be glued into the enclosure
with silicone glue (I use E-6000, which is available at
Wal-Mart). —Gerald Weber, Kendrick Amplifiers.