Hi, thanks for all the responses, the circuit is meant to be a filter, the switch between pins 8 and 9 and the output is to toggle between lowpass and bandpass, and the 47k pot is meant to control the Q factor aka resonance. Finally the switch between the 100k pot and the jack socket is to toggle between manual control of the cut off and use of an external LFO that I ve built. Sorry the schematic isn't very clear I was in a bit of a hurry, hopefully this clarifies. I m pretty sure there is problem with the bias as the circuit seems to respond better when when the 3k9 resistor is replaced with with variable one so that the bias can be adjusted accordingly, maybe a diode would do the trick?