Plexitone WAY too much output/boost.

[Herostratus]

Hi all. I have finished building my first pedal, and to my surprise it has basically been successful. It is the tayda plexitone PCB (I know!, I wont do it again). I bought it before I'd read much of these forums and didn't realise there were a few strong opinions about them. The thing sounds good, and has the full and creamy sort of overdrive that I was expecting. The problem is that its output is way louder than when the pedal is in bypass. Even with the output volume at zero, it seems several times louder than the bypassed signal. And with the "boost" engaged it is even worse. I finished It a few night ago and have been double checking everything. I did try increasing the value of the resistor first in line after the input. This tamed it a little, but I guess is not the right fix, and have put it back to original. The only component which deviated from the bill of materials is the ICL7660SCPA which was substituted with an ICL7660CPAZ, as this was all tayda had in stock. I don't know what the differences are, but cannot find anywhere where its says they may or may not be compatible. Could this be causing my problem? Are there any simple noob gotchya's which may cause this?

[Herostratus]

And no its not in the box yet!