I didn't have any succes with getting this thing to work with a RC filter on the power supply as suggested her: http://www.geocities.com/tpe123/folkurb ... ppets.html
I tried building it without the filter which gave me a loud tone from the VCO at all times. However, if a 1K resistor and a led is connected from +9V to GND before the chip's power pin, it is almost quiet until it's fed with an input. I also added a switch to select a range for the VCO and pot to attenuate the output. This is an easy build if you want a very decent ring modulator-like effect. Could probably use a buffer on the input.