Goodwood Audio Interfacer (Underfacer)

[isaiahcarrell1]

The schematics are not available anywhere, but I'm having trouble figuring out the stereo to mono sum function of this unit. I'm looking to build one as it is a utility pedal that would be very good to have on my board. Any help?

https://goodwoodaudio.com/product/theunderfacer/