Here are some modifications I made to the standard wah pedal circuit over 10 years ago.    You can still get the genuine standard sound, but in addition, you get:

• A Resonance control to make the wah sharper or broader
• A Frequency switch to select different frequency ranges
• True bypass when switched out of circuit

It's somewhat disappointing seeing pedal released in 1997 touting these features as some type of breakthrough.   I'm sure its physically and electronically a very good pedal, but maybe I missed my calling 10 years ago!

Here are the changes:

Your wah circuit will be similar to the one above, although some component values may vary.   The changes to make are:

• Replace the 33K resistor across the coil with a 10K resistor in series with a 50K Linear pot.   When this pot is centred, the standard value is restored.
• Switch different value capacitors for the standard 0.01 value at one end of the coil.   Increasing this value 4 times decreases the frequency range by a factor of 2.   There are some suggested values on the circuit for a 5-way switch, where the centre position is standard.   The 1M resistors prevent a loud popping sound when you turn the switch.
• Replace the SPDT footswitch with a DPDT switch and wire it as above for a true bypass switch.   Note the addition of a 1M resistor on the input switch.

Here How I Did It:

The right way to do this is with a small extra pc board to accommodate the new components, firmly secured inside the case, and wired carefully and neatly.    Unfortunately, I did none of these things, but its worked for 10 years and if it ain't broke ...

I used a pot for the resonance control mounted just forward of the socket on the side of the case, and I used a three position ON-ON-ON mini-toggle (these can be wired as a single pole, 3 way switch) for three frequency ranges.   This switch is small and fits behind the socket.   You could use a rotary switch, but you need to be sure it fits in the case, of course.

I wired the 1M resistor direct on the circuit board, and *carefully* removed the .01uF capacitor and 33K resistor, wiring a 10K resistor soldered at one end only.    This is really quite shabby, but given that its all enclosed, has been reliable.

Equally shabby, the 1M resistors are located on the back of the switch, with the 3 capacitors wired at one end on the switch and all wired together at the other end.    Using caps with solid wires this is really quite strong, but doesn't look good, and would not pass any serious quality inspection.

Nevertheless, its a foot pedal, and gets kicked around, and it still works.    I should admit that despite this new flexibility, 95% of the time I use the standard settings.