I was sent this dual filter for repair which I had not seen before. The module header says Solid State Music Filter Set 2040 and the logo and footer refer to Solid State Micro Technology. This filter requires a SSM2040 which is hard to find, or a Hearn Morely HM2040 submodule, which this filter uses.

It is two separate filters, a 24 dB low pass filter, and a multi-mode resonant filter. The multi-mode resonant filter can be used to modulate the 24 dB low pass filter which creates some interesting timbre

It is a two PCB set, of which the panel PCB mounts all the potentiometers. The switches and jacks are mounted to the panel and wired to the PCB. All of the active circuitry is on the rear PCB.

Operation

The 24 dB low pass filter is quite nice. It has rich resonance as can be seen in this scope photo.

The signal input attenuators and the modulation attenuators provide plenty of control. This scope image is verifying the modulation inputs which attenuate the 200 Hz audio signal.

The multi-mode filter has rich resonance as well. These three scope images show the LP, BP, and HP modes with some resonance.

This scope image shows the 24 dB low pass filter being modulated by the multi-mode filter (magenta & green) using the lower switch.

This image shows the same setup with the upper switch engaged. I'm not exactly sure what the specific function is but it produces some nice results.

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