An LC filter is useful in forming a bandpass EQ, and often a gyrator circuit is used in place of the inductor to reduce costs and save space.
Gyrator bandpass filters are found in tone controls or as frequency shapers in “metal” pedals.
I have programmed a calculator to make it easy to find the center of the passband of the filter.
It can be accessed from the AMZ Lab Notebook or by this direct link.
Can you find the gyrator filters in this pedal?
Here is a small schematic that shows the equivalent circuit of the gyrator bandpass filter described above:
Another schematic as an example, this one is a 10-band EQ.
http://www.muzique.com/news/images/10band.gif
Wow, I just happen to have a Metal Maniac FX 58 pedal that has the same pc board, but slightly different values. It looks to have a pretty good boost in the mid-range. I’m going to remove that for a more notched sound.
From looking at the schematics at Free Info Soc. it appears that DOD got at least 3 different pedals out of this. The one pictured, the Metal Maniac that I have, and the Thrash Metal. It’s a pretty cool system in that you can use all the same parts and change a couple of caps in the gyrators and have a new EQ and pedal. As guitar EQ trends change, you come up with a new pedal every few years!