Mid boost pedal design

[Phoenix]

Hi everyone,

Just thought I'd share a design I've been working on, it's a clean boost with variable frequency and shelving high and low pass second-order filters. It's intended for metal styles to replace the typical Tube Screamer used as a mid boost to tighten up heavy overdriven tones, with greater flexibility over tone and available boost.
It provides a maximum of 40dB of boost, with soft clipping on overload. Due to the high value of the gain pot in the feedback path of the first op amp, the junction capacitance of a typical zener diode is high enough to cause significant high-frequency roll-off, so the zener is enclosed in a 1N4148 bridge rectifier to lower its capacitance and prevent this roll-off when the gain is set to high values.
The high-pass filter is variable between approximately 32Hz and 620Hz, and the low-pass filter is variable between approximately 140Hz and 5.6kHz. The high-pass uses two variable gyrators, and the low-pass uses two variable capacitor multipliers.
For this design I'm using a plastic battery enclosure that is accessible without the need for a screwdriver or other tools, and this battery box prevents the battery from being inserted backwards, so I have omitted reverse polarity protection from this design.
The TC1044 provides +/-9V rails, so with TL074's there's approximately 12V peak-to-peak headroom as limited by the zener clipper, which is more than enough to overdrive a typical tube amp input stage.
As the design stands at the moment, it requires 7 op amps, so using two quad packages there is a spare op amp. I haven't thought of a use for it, or any other way to reduce the required op amps to 6 so I could use one quad and one dual package. Any suggestions on that front would be greatly appreciated.

Anyway, thought somebody might be interested in this, let me know what you think!

[GibsonGM]

NICE!  Impressive work....

[Phoenix]

Thanks Mike.