This one is pretty “bare bones,” and it’s a really good sounding boost for bass, too. I found the schematic at amzfx. When I built it, I didn’t have 430K and 43K resistors, so I used a 390K and a 39K. I also added a switch that takes out the 39K resistor that goes to ground. Switching it out gives the bass boost a slightly brighter “punchy,” sort of compressed, fuzzy tone. In the future, I might try using this as a front or back-end boost added on to another effect.