I breadboarded the distortion PCB today and it works as it should.
As designed the overdrive is effective from above 5v, and tops out at approx 10V for soft clipping and a bit higher for hard. This means that the output is a lot louder when distorted, but that can be adjusted using the gain pot.
Take these considerations when wiring on the breadboard:
- If no filter caps are used, you must put a wire between the two HP pins (3 and 4).
- Use a 200/100k resistor divider from 15v to a positive input opamp buffer to get 5V for the logic level
- Use a 10k resistor to GND on the clip mode pin, then you can use a wire from clip mode to 5v to change mode without removing the GND connection
- Input/output: I used my i/o module. Input should be amplified 5x (2x att, 10x gain), output should be attenuated 5x (10x att, 2x gain). Even with this, the input is not high enough to distort. I had to add an additional inverting amp (10k input and 100k feedback resistors, 10x gain) to get proper distortion.
PS: I have a couple of errors on the I/O board: the 1/4" jacks have Tip and Ring swapped so it shorts when using a mono cable. Also, the silk screen is wrong, it says that Gain is 2x when jumper is open and 10x when closed, it should be the other way around. Also, it seems that there is a fair bit of HF loss but that may have been before I got att/gain set correctly.
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