Have a pedal with no tone control? Want to build a stand-alone tone control? Want to design a tone control that is specific to your needs with a minimum of parts? Then the Big Muff Pi tone control is for you. It is a great place to start because it is so simple you can build it with just 5 parts. It is also a great test-bed to add mods and experiment with.
Five parts and bit of wire--that's all there is to it.
Because the circuit is so simple, you can build it right on to a potentiometer without any type of PCB. This approach saves enough space that you can actually mount the entire tone stack and the pot in an existing pedal that has enough room for a pot. Orient the potentiometer as shown. Start with the two resistors. Solder them directly to the pot lugs. Then add the a caps. Finally, add an input and ground wire. That;s where you;ll hook it into an existing circuit.
The indomitable Jack Orman (www.muzique.com) has researched the Big Muff Tone control and suggested various improvements. One of these improvements is to add a Body pot that provides more control over the response of the circuit. This version uses a 3.3k ohm resistor in place of the stock 22k value, and adds a 25k pot to ground. This provide you with a tone control that can handle both flat and 'scooped'; frequency responses.
As with the original version, you can build the circuit on a set of two pots.
Because the circuit uses very few parts, you can build one into a small enclosure with in and out jacks. The result is a small battery-free tone control that you can insert in various parts of your effects chain where you need control over tone. The Hammond 1590A enclosure is ideal for our purposes. It measures 3.64" x 1.52" x 1.06"--just enough to hold the components. Here's the wiring diagram:
You'll notice that the tone stack does not have any power connections. That's because it is a passive circuit--good for simplicity but it does come with a cost. Passive components in a tone stack configuration will reduce the output of the device you attach it to--whether it an effect pedal or an amplifier. Active tone stacks do not have this limitation, but require power and generally more parts. Try the BMP tone stack on various pedals and amps and you can quickly tell if it is removing to much signal. If that's the case, consider putting the tone stack after a booster to make up for lost signal.