Info about the project:
The Spackler is a modified version of the Demeter® Fat Control™. The effect is a midrange boost that will push the front end of an amplifier while boosting the lower-mid frequency range resulting in what some might call added “warmth” and “depth” to a guitar signal. The Fat Control™ works well as a standalone effect, or before another effect like a dirt box. The Spackler adds one extra control for the total gain amount available for the boost.
The stock design has a buffered bypass. While some may find this useful, the Spackler allows you to also wire in a hard bypass.
The controls are as follows
GAIN: This control allows you to vary the overall gain produced by the circuit. At fully counterclockwise the gain will be approximately that of the bypassed signal. At fully clockwise gain will increase for added volume and midrange boost.
FAT: This control blends between the “buffered” and mid boosted signals. Note that the first stage of the opamp is not a true buffer, but it will sound just like one if you hook the Spackler up using the buffered bypass wiring diagram below.
I can't find a vid of the Spackler, but just imagine this with a gain control :o)