Yes, I agree…the loudness is probably just the gain pot over adjusted.
When the pedal is engaged, does it sound different than in bypass (other than it being louder)?
On the middle pin of depth knob…Are you getting a variable DC voltage between 0 and 5V as you turn the knob?…or is it always at some low voltage, close to 0V?
Are Q1 and Q2 installed properly?
Are you hearing both channels (high and low) fine in calibration mode?
-Brach