I have a Big Muff Pi V4 that I purchased around 1980, which worked really well for a number of years. Recently I tried to use it and noticed, as with other forum users, the signal from the pedal is stronger than when plugging the instrument directly to the amplifier. However when I engage the foot switch I no longer get the rich tone but rather a really weak distorted sound, like the sustain is on full, but the volume is basically non existent. I changed the 9 volt battery however the same problem exists. When I flip the by pass switch there is no change. Any ideas?