This was first published in two different places: PedalPCB forum and Reddit.
Disclaimer
Please exercise safety when building pedals. While the voltages being worked with are small, be mindful of electrocution. Wear proper safety gear, take breaks, and solder in a well-ventilated room. I don’t offer any sort of technical assistance and these build logs are meant for educational purposes only. Proceed with caution.
Also, I am not associated with any of the companies or groups/people mentioned in this post. I patronized their businesses and entities so I would like to share/promote them.
Build Log
I used this schematic that I redid from FSB. Gray Bench Electronics also did a teardown of the pedal that showed a few variances like the Bass potentiometer (C500K -> C1M), the Gain potentiometer (B100K dual gang -> A100K dual gang), and JFET selection.
PCB was designed in Eagle. I did do a version to allow for SMT JFETs; however, the SMT versions of the JFETs are not available at this time. I opted for a J201 for the first JFET sourced from PedalPCB and 2N5457 for the other JFETs sourced from StompBoxParts. I also changed all the trimmers to 50K because the 10K on the Bias control didn't allow me to adjust the voltage appropriately. I put some "empty pads" on the PCB so I could easily adjust the voltages with my multimeter probe. Chuck's insight about biasing JFETs and this runoffgrove article helped with the biasing of the JFETs. One of the challenges was making the Bias control (not to be confused with the bias trimmers) to work, and I did need to change the source resistor (R8) of Q3 to 100R from 1K. Furthermore, some of the JFET transistors from my pile did require 100R for R10 on Q4 as well in order for the JFET to bias correctly.
I built this in a 125B Pro from StompBoxParts. I highly recommend it; it's legitimately one of the best looking plain aluminum enclosures I have ever seen. My drilling was a bit off and I had to drill bigger potentiometer holes to allow for more "play" to allow better positioning, but I think it turned out fine. Graphic art is from Daiso, a Japanese dollar store in my area. The overall schematic reminds me of a Big Muff but upon closer inspection, the topology is more like the Fairfield Circuitry Barbershop with passive EQ controls and a dual gain stage.
Updates
7-17-2023: Corrected schematic with updated values. Uploaded relevant files to GitHub. Shared PCB on OshPark.