The 4730 is a second order state variable filter with low pass, band pass, and high pass outputs. The filter has a high / low range, resonance, and a sweep/track mode. The filter should be set to track when the filter is being controlled by a keyboard (e.g. tracking a VCO), and set to sweep when the CV will go to 0V (e.g. a LFO as the CV). This kit was $37.95 in the 1976 catalog.
4730 PAiA Filter Manual
4730 PAiA Filter Schematic
These are the PCB traces. The three trimmers were previously converted to multi-turn and the traces repaired on the right.
I upgraded the jacks, sockets and the LM3900 and 748 op-amp, and replaced the electrolytic capacitors. I used bi-polar for the output capacitors and added 100K bleed resistors. I upgraded the 748 IC to a TL071 and removed the compensation capacitor. The power cable terminates in a 4 pin MTA connector.
An external CV must be applied in order to set the initial frequency. Calibration is straight forward but requires a number of passes. This scope image shows the filter self-oscillating. It would only self-oscillate with a 5V CV and at maximum control settings. The waveforms are Input, LP, BP, and HP.
This scope image shows a frequency setting where all three outputs are near-sine shape.
This scope image shows filtering of a square wave with no resonance.
This scope image shows the same control settings with some resonance.
This scope image shows the same settings with maximum resonance.