***ignore this post and look two posts down, instead****
The layouts look wrong to me. Referring to
this schematic, pin 5 of the upper TL072 and Level 1 should both be connected to VD, not ground. VD is a voltage divider, basically a duplicate of VB. I suspect this was misread as V0 and interpreted to be ground.
Try moving Level 1 to row 9 (from the top), just below the output lead. The jumper between rows 9 and 10 should either go from row 9 to row 11 (it will have to be angled) or it can go sideways to counteract the cut at the 10th column (from the left).
I don't know if this is the only error, or if this will fix it, but it's worth a try. I assume Wampler used two voltage dividers to reduce noise, but you can almost certainly get away with just one.