I finished this 4020 Resonant Filter Set for my own system. It is a combination of three filters, a LM3700 SVF, a CEM3328 LPF, and a SSM4020 LPF. There are various interconnections between the filters that make this set quite interesting and useful. All outputs are across the top. The vari output is from the SVF LP-HP control and has a level control as the input to the CEM filter and a switch as an input to the SSM filter. The CEM filter also has a switch to add either the SSM or SVF outputs as its input.

The violet banana jack is the unattenuated vari output and can be shorted to the SSM C modulation input banana jack to modulate that filter as well. Here's a block diagram of the filter set. showing the various interconnects.

Construction

This is a two PCB set with all the active components on this rear PCB. The top is the SSM filter with an adapter used as the SSM2040, the middle is the CEM filter, and the bottom is the LM13700 filter.

Operation

With two signal sources and three outputs, my 4 channel scope doesn't have enough inputs. These first photos show the SRV in (yellow), SSM in (cyan), SRV Vari out (magenta) and SSM out (green). The SSM is modulating the SRV so the green channel is slowly morphing over time. These three photos show the change over time.

For these three photos, I changed cyan to the CEM output. Again, the photos show the change over time.

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