I think this will be popular with quite a few people, especially those who want to get the most of their dirt pedals and fine tune the frequency response more effectively. I think this would go to make the perfect distortion pedal if you put your favourite dirt circuit with this in a dual effect box, particularly with an order switcher so you could put the tone control before or after the dirt. The IC is supplied with +/- 9V and I have altered the circuit slightly to use my preferred method of doing this with a ICL7660S to provide the bipolar supply.
Note that the original is advertised as being capable of accepting a supply from +/5V to +/-18V. However, the ICL7660S can accept a maximum of only 12V and so I would suggest keeping the supply at 9V if you use the suggested charge pump IC. That still gives you an 18V swing which I expect would be more than adequate for this, but if you would prefer to use an 18V supply for additional headroom then you could use an ICL7662 which is rated for up to 20V although these may be more difficult to find and certainly more expensive.
Info about the original project from the author:
Deflnltlon: Offers flexible control over tone by creating several different response options. Low pass response boosts low frequencies and attenuates high frequencies; high pass response boosts high frequencies, and attenuates low frequencies; bandpass response boosts a specific frequency range; and notch response attenuates a specific frequency.
The “state variable” filter is a type of filter used in several synthesizers to control timbre; this circuit is a variation of the state-variable filter that has been optimized for tone control purposes. It offers considerably more sonic flexibility than the tone controls found on most instruments and amplifiers.
. Variable resonance control changes “sharpness” of the sound
. Easily resettable to fiat response
. Low-pass, high-pass, the band pass outputs alre individually mixable via an onboard mixer to create highly complex responses
. Useful as recording studio or PA equalizer
. Operates at low level or line level
